P0238 Turbocharger/Supercharger Boost Sensor A Circuit

This text explains the meaning, symptoms, possible causes, and diagnostic and repair procedures for error code P0238. This code is a generic diagnostic trouble code (DTC), meaning it can apply to all vehicles equipped with a turbocharger, including brands like VW, Dodge, Mercedes, Isuzu, Chrysler, and Jeep.

Simply put, code P0238 indicates that the Powertrain Control Module (PCM) has detected an abnormally high voltage from the turbocharger boost pressure sensor at a time when the turbocharger should not be producing pressure (no boost requested).

Here is a breakdown of the key points:

  • What is it? A standard error code for turbocharged vehicles.
  • How does the boost pressure sensor work? It is a variable resistor powered by a 5-volt signal from the PCM.
    • Low pressure = high resistance = low return voltage to the PCM (approximately 0.5 volts).
    • High pressure = low resistance = higher return voltage to the PCM (approximately 4.5 volts).
  • When is code P0238 triggered? When the PCM receives a voltage higher than 4 volts from the boost pressure sensor while no boost is requested.

Common symptoms of code P0238:

  • The check engine light illuminates.
  • The PCM enters “limp mode,” which results in:
    • Significantly reduced acceleration.
    • Limited boost pressure.
    • Retarded ignition timing.
  • The PCM ignores data from the boost pressure sensor and uses a default value.

Possible causes of code P0238:

  • Problems with other sensors or the 5-volt reference circuit (Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor).
  • Intermittent wiring issues (loose or faulty connections).
  • A faulty boost pressure sensor (“A”).
  • A short to voltage in the boost pressure sensor circuit.
  • A faulty Powertrain Control Module (PCM).

Suggested diagnostic and repair procedures:

  1. Check for other error codes: If other codes are present (especially those related to IAT, ECT sensors, or the 5-volt reference), they should be resolved first.
  2. Consult Technical Service Bulletins (TSBs): Check if the manufacturer has released specific information or known fixes for this issue on your vehicle.
  3. Wiggle test the wiring: With the engine running, gently shake the wiring harness near the boost pressure sensor to see if it triggers the fault. If it does, inspect the connections carefully.
  4. Check the sensor supply voltage: With the sensor disconnected and the ignition on (engine off), measure the voltage at the sensor’s power connector. It should be 5 volts. If not, the problem could be with the PCM.
  5. Check the sensor signal voltage: Reconnect the sensor and, with the ignition on (engine off), measure the voltage at the sensor’s signal wire. It should be approximately 0.5 volts. A significantly higher voltage suggests a faulty sensor.
  6. Warning: Never use an incandescent test light to test the boost pressure sensor circuits, as this could damage the sensor or the PCM. Use a digital multimeter.

Importance of prompt repair:

The text emphasizes that it is important to resolve this issue quickly due to the increased risk of catalytic converter damage when the engine runs in “limp mode” for an extended period.

P0239 Turbocharger/Supercharger Boost Sensor B Circuit Malfunction

What does it mean?

This diagnostic code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996 and newer), although specific repair steps may vary slightly by model.

The P0239 code is generic in that it refers to a problem in the turbocharger/supercharger boost sensor A circuit. Although generic in nature, never assume it is identical for all vehicles.

 

OBD codes do not necessarily point to a specific component, but rather to an area where the technician can look for possible causes of a problem within that circuit, which could include multiple possibilities.

All vehicles with the P0239 code have one singular point in common. It refers to an unacceptable discrepancy between the ECM’s (Electronic Control Module) programmed percentage of turbo boost at a specific RPM and the sensor signal value. These two values must coincide within close limits.
How turbocharging (forced induction) increases performance

Turbochargers force much more air into the engine than the engine is capable of under normal aspiration conditions. The greater the volume of air forced into the cylinders, the greater the increase in fuel equates to increased power.

Typically, a turbocharger can increase power by 35 to 50% in an engine specifically designed for turbocharging. The components of a conventional engine will not withstand the stresses placed on it by forced induction.

Turbochargers offer high power gains with little to no negative effects on fuel economy. They use exhaust speed to propel the turbocharger, so it’s essentially free power. That’s the advantage. The disadvantage is that they take a beating and tend to fail at unpredictable times for a multitude of reasons. When an indication occurs that a problem with the turbocharger has happened, resolve it as soon as possible. A turbocharged engine greatly exaggerates engine problems due to the mass of compressed air.

Never tighten the wastegate and do not attempt to install any modification on a stock turbocharged engine to increase boost pressures. The fuel and timing curve of most engines will not adapt to boost pressures higher than normal and engine damage will occur.

Note: This DTC is basically identical to P0235 which refers to turbocharger “A”.

Symptoms

Symptoms of a P0239 diagnostic code may include:

    The P0239 code will be set, which simply means a problem exists somewhere in this circuit preventing proper boost control. Additional progressive codes may be set regarding this malfunction, each relating to a section of the circuit.
    The engine may lack acceleration.
    The boost pressure gauge will indicate less than 9 pounds of boost or more than 14 pounds of boost. Both are out of range.
    Unusual noises or rattling from the turbocharger or piping.
    The engine knock sensor code may appear, indicating detonation due to high cylinder head temperatures.
    The engine may exhibit a general lack of power.
    Exhaust smoke.
    Fouled spark plugs
    Abnormally high engine temperature at cruising speeds.
    Hissing noises at the wastegate

Causes

Turbochargers typically spin at an incredible speed of 100,000 to 150,000 RPM. They are not the most tolerant of imbalance conditions or lack of clean oil to the bearing.

Causes

potential causes of this DTC include:

    Vacuum leak at the intake manifold
    Dirty air filter
    Faulty wastegate – stuck open, closed, or leaking
    Insufficient oil supply to the main shaft bearing – obstruction in the oil supply or return line.
    Bearing failure causing slow rotation due to drag.
    The bearing wobbles and the turbine blades hit the turbo housing.
    Chipped, twisted, or missing turbine blades, causing imbalance.
    Oil seal leak on the compressor side of the turbo, as shown by oil in the turbo and fouled plugs.
    Excessive axial play in the turbo
    Faulty intercooler
    Loose connections between the intake pipe and the throttle body
    Cracks in the turbo housing
    Loose exhaust manifold at the turbo bolts.
    Poor electrical connection to the Turbo boost sensor.
    Short or open in the sensor harness between the sensor and the ECM.
    Faulty sensor or ECM 5-volt reference driver.

 

Diagnostic steps

and possible solutions

From my experience, the diagnostic flow starts with the most common turbo problems and works systematically down to the least likely. Simple tools are needed, such as a vacuum gauge and a dial indicator.

    Confirm that the engine is running correctly, without faulty plugs and without codes related to a faulty knock sensor.
    On a cold engine, inspect the clamps at the turbo outlet, the intercooler, and the throttle body for tightness.
    Try to wiggle the turbo on the exhaust flange to see if it is tight.
    Inspect the intake manifold for leaks of any kind, including intake hoses.
    Remove the wastegate actuator. Operate the valve manually while checking for a sticky valve causing low boost.
    Locate an unused vacuum port on the intake manifold and install a vacuum gauge. Start the engine. At idle, the engine should have between 16 and 22 inches of vacuum. If it has less than 16, the catalytic converter is bad and will not allow boost to build.
    Quickly rev the engine to 5000 RPM and release the throttle while observing the vacuum gauge as it displays boost pressure. If the boost pressure exceeds 19 pounds of boost, you have a bad wastegate. If the boost does not rise between 14 and 19 pounds of boost, a problem exists with the turbo itself.
    Stop the engine and let it cool. Remove the turbo outlet pipe and look inside the turbo to see if the blades are hitting the sides of the housing. Look for twisted or missing blades or oil in the turbo. Spin the blades by hand and look for grinding or resistance indicating a faulty turbo.
    Inspect the oil lines from the engine block to the turbo center bearing and the return line from the bearing to the oil pan for leaks.
    Install the dial indicator on the turbine output nose and move the turbo shaft in and out. If there is more than 0.003 axial play, the center bearing is faulty.
    If the turbo passes these tests, it is good. Use the service manual to test the boost sensor and harness using a volt/ohmmeter. Locate the ECM’s 5-volt reference to the sensor and confirm the voltage. No voltage present indicates an open or short in the harness or a bad ECM.
    Locate the appropriate reference signal from the boost sensor to the ECM and confirm a variable voltage as the RPM increases. No voltage rise indicates a bad sensor.

 

P023A Open Charge Air Cooler Coolant Pump Control Circuit

Code P023A indicates an open circuit in the control system of the charge air cooler coolant pump (Charge Air Cooler or Intercooler). This system is used in forced induction engines (turbocharged or supercharged) to cool the compressed air before it enters the cylinders, thereby improving combustion efficiency.

System Operation

  • Charge Air Cooler (Intercooler): Cools the compressed air via an air/liquid or air/air heat exchanger.
  • Dedicated Coolant Pump: An additional electric pump ensures coolant flow to the intercooler, independent of the main water pump.

Code Severity

  • Risk Level: Low (no immediate danger), but may lead to:
    • Decreased engine performance.
    • Localized overheating.
    • Increased fuel consumption.

Common Symptoms

  1. Malfunction Indicator Lamp (MIL) illuminated.
  2. Loss of power during acceleration.
  3. Abnormal temperatures (especially under high engine load).
  4. Risk of pre-detonation (knocking) due to uncooled charge air.

Possible Causes

Category Details
Electrical Issues – Open circuit in the pump wiring.
– Corroded/disconnected connector.
– ECM (Engine Control Module) failure.
Mechanical Failures – Seized coolant pump (debris, corrosion).
– Obstruction in coolant lines.
Diagnostic Errors – Insufficient or degraded coolant.
– Air bubbles in the system.

Diagnostic Steps

1. Preliminary Check

  • Check TSBs (Technical Service Bulletins): Look for known recalls or software solutions for your model (e.g., Ford EcoBoost, Mazda Skyactiv).
  • Inspect coolant: Level, quality (no contamination), and purge any air bubbles.

2. Locate the Coolant Pump

  • Typical location: Near the intercooler, often behind the grille or under the hood.
  • Identify lines: Follow the coolant hoses from the intercooler.

3. Electrical Test (Multimeter)

  • Disconnect the pump and check:
    • Resistance: Compare with manufacturer specifications (typically 5-20 Ω).
    • Continuity: Between the pump and ECM (look for open or short circuits).
  • Inspect the harness: Cracks, burns, or corrosion on connectors.

4. Mechanical Pump Test

  • Direct power: Use an external 12V power source to check if the pump operates.
  • Flow: If the pump runs but no flow, suspect internal obstruction.

5. ECM Diagnosis

  • Advanced OBD2 scanner: Check live data (pump control signal).
  • Pin test: Measure ECM output voltage to the pump (should be ~12V upon activation).

Common Repairs

Problem Solution Estimated Cost
Faulty pump Replace the pump. 150-400 € (part + labor)
Open circuit Repair wiring or replace connector. 50-150 €
Poor connection Clean terminals or replace connector. 20-80 €

Post-Repair Best Practices

  1. Reset the code with an OBD2 scanner.
  2. Road test: Verify the pump activates under load (using a live diagnostic tool).
  3. Monitoring: Check temperatures and performance over several driving cycles.

Do Not Ignore

If code P023A reappears after repair, check:

  • Coolant compatibility (some models require a specific type).
  • ECM software updates (some manufacturers fix bugs via recall).

ℹ️ Pro tip: On high-end vehicles (e.g., Audi, BMW), use a manufacturer-specific diagnostic tool (e.g., VCDS, ISTA) to access specific cooling system parameters.

P023B Low Value in Charge Air Cooler Coolant Pump Control Circuit

What Does It Mean?

This generic powertrain diagnostic trouble code (DTC) generally applies to all OBD-II equipped vehicles with a charge air cooler. This may include, but is not limited to, vehicles from Ford, Chevy, Mazda, Toyota, etc.

In forced induction systems, they use a charge air cooler or what I’ll call an intercooler (IC) to help cool the charge air used by the engine. These operate similarly to a radiator.

In the case of the IC, instead of cooling antifreeze, it cools the air to produce a more efficient air/fuel mixture, which in turn leads to better fuel economy, improved performance, etc. In some of these systems, the IC uses a combination of air and coolant to assist in cooling the forced charge air entering the cylinders via forced induction (supercharger or turbocharger).

In these cases, to meet additional coolant flow demands, a coolant pump is used. Generally, these are electric fluid pumps that essentially provide the necessary coolant flow to the IC that the water pump cannot provide independently.

The MIL (Malfunction Indicator Lamp) illuminates on the instrument cluster with P023B and related codes when it monitors a condition outside a specific range in the IC coolant pump control circuit. Off the top of my head, I can think of two causes: one is an obstruction in the pump’s openings causing an electrical value out of range. The other is a rubbed control wire that has severed the electrical connection, causing an open circuit. The point is that both mechanical and electrical faults are possible.

Code P023B, the Charge Air Cooler Coolant Pump Control Circuit Low, is active when there is a low electrical value in the charge air cooler coolant pump and/or its circuit.
How severe is this DTC?

The severity in this case would be low. In most instances, this fault will not present any immediate safety issues. That said, vehicle drivability and performance may suffer, especially if left unaddressed for long enough.
What are some of the symptoms of the code?

Symptoms of a P023B engine code may include:

MIL (Malfunction Indicator Lamp) illuminated
Poor engine performance
Poor fuel economy
Irregular/abnormal engine temperatures

What are some common causes of the code?

Potential causes may include:

Internal mechanical obstruction in the coolant pump
Coolant pump wiring harness broken or damaged
ECM (Engine Control Module) issue
Pin/connector problem (e.g., corrosion, broken locking tab, etc.)

What are the troubleshooting steps for P023B?

Be sure to check Technical Service Bulletins (TSBs) for your vehicle. Accessing a known fix can save you time and money during diagnosis.
Basic Step #1

You first need to locate your IC (Intercooler, AKA Charge Air Cooler). Generally, these are located where they can receive optimal airflow (e.g., in front of the radiator, inside the front bumper, under the hood). Once located, you’ll need to find the coolant lines/pipes to trace back to the coolant pump. It might be tricky to find as they are typically installed in-line with the coolant flow, so keep that in mind. Given the temperatures the cooling system is exposed to, it would be wise to carefully inspect the harness around the area for signs of melting or similar issues.

NOTE: Make sure to let the engine cool down before testing or repairing the cooling system.
Basic Step #2

Check the integrity of your cooling system. Check your coolant levels and also the health of the coolant. Ensure it is clean and full before proceeding.

NOTE: Refer to your service manual to check which specific antifreeze is used for your particular make and model.
Basic Tip #3

Measure and record the integrity of the charge air cooler control circuit. Equipped with a multimeter and the appropriate wiring diagram, you may be able to independently test the control circuit. This might involve disconnecting the connector at the ECM (Engine Control Module) and the other end at the coolant pump. Refer to your wiring diagram for specific wire colors and testing procedures.

NOTE: Ensure the battery is disconnected before performing any electrical repairs.
Basic Step #4

You might be able to independently test the coolant pump depending on your specific system. After all, they are just electric pumps. Refer to the service manual before proceeding, as this might not apply to you. Equipped with a 12-volt power source and a good ground, you can remove the coolant pump from the vehicle (this may involve draining the system) and power it up to see if it activates at all. If it does, you may want to ensure it can also transfer fluid (for reference, these pumps aren’t meant to have a huge amount of pressure or flow, so just inspect the general operation here).
Basic Step #5

ECM diagnosis is always a last resort, but sometimes it can be done with relative ease. This typically involves performing a pin test at the ECM itself and comparing your readings to the desired values. I must emphasize that all other diagnostic strategies should be exhausted beforehand.

P023C High Boost Air Cooler Coolant Pump Control Circuit

Meaning of Code P023C

This generic OBD-II code applies to vehicles equipped with a charge air cooler (intercooler). It indicates an abnormally high electrical value in the control circuit of the coolant pump associated with the cooler. This system cools the air compressed by the turbocharger or compressor to optimize engine performance.

Severity

Low level:

  • No immediate safety risk.

  • Possible impact on performance, fuel consumption, or engine temperature if unresolved.

Common Symptoms

  • Check engine light on (MIL).

  • Loss of power or sluggish acceleration response.

  • Increased fuel consumption.

  • Unstable or abnormal engine temperatures.

Possible Causes

  1. Mechanical obstruction in the coolant pump.

  2. Electrical issues:

    • Damaged, chafed, or cut wiring harness.

    • Corroded, oxidized, or improperly connected connector.

  3. Pump failure (electric motor burnt out).

  4. ECM failure (rare, check last).

Troubleshooting Procedure

Step 1: Check Technical Service Bulletins (TSB)

  • Verify if the manufacturer has released any fixes for this code on your model.

Step 2: Locate and Inspect the Cooler and Pump

  1. Locate the intercooler: Typically near the radiator or front bumper.

  2. Inspect coolant lines:

    • Look for leaks, cracks, or corrosion deposits.

    • Check coolant level and quality (refer to the manual for the specific type).

⚠️ Precautions:

  • Work on a cold engine to avoid burns.

  • Disconnect the battery before any electrical work.

Step 3: Test the Electrical Circuit

  1. Check wiring and connectors:

    • Look for chafed wires, melted insulation, or oxidized pins.

    • Clean connectors with contact cleaner spray and apply dielectric grease.

  2. Measure continuity and resistance:

    • Use a multimeter to check for no short circuits or open circuits.

    • Compare values with manufacturer specifications.

Step 4: Test the Coolant Pump

  1. Direct power supply:

    • Remove the pump (drain the circuit if necessary).

    • Power it with 12V (external source) to verify operation.

    • Ensure it generates minimum flow (even if weak).

  2. Mechanical inspection:

    • Check for obstructions (debris, deposits) in the inlet/outlet ports.

Step 5: ECM Diagnosis

  • Measure ECM output signals to the pump using an oscilloscope or diagnostic tool.

  • If in doubt, consult a professional for ECM reprogramming or replacement.

Recommended Solutions

  • Replace the pump if faulty (average cost: €100 to €300).

  • Repair the wiring harness: Replace damaged sections and secure fastenings.

  • Clean the cooling circuit if contaminated.

Final Precautions

  • Reset the code after repair and test the vehicle over several driving cycles.

  • Use original parts to ensure electrical and mechanical compatibility.

P023D MAP – Turbo/Supercharger Boost Sensor A Correlation

What Does It Mean?

This is a generic powertrain diagnostic trouble code (DTC) that generally applies to OBD-II vehicles. This may include, but is not limited to, Land Rover (Range Rover, Discovery), Ford, Chevrolet, Mazda, Dodge, Peugeot, Saab, Toyota vehicles, etc.

Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

If your OBD-II equipped vehicle has stored a P023D code, it means the powertrain control module (PCM) has detected a discrepancy in the correlation signals between the manifold absolute pressure (MAP) sensor and the turbocharger/supercharger boost pressure sensor that has been designated “A”.

The “A” designates a specific boost pressure sensor in a system that may use multiple boost pressure sensors at different locations. Consult a reliable vehicle information source to accurately determine which sensor the A references (for the vehicle in question). This code applies only to vehicles equipped with forced air induction devices. Forced air induction devices include turbochargers and superchargers.

The MAP sensor provides the PCM with a voltage signal that reflects the density or pressure of the air in the intake manifold. The voltage signal is received (by the PCM) as kilopascal (kPa) units or inches of mercury (Hg). In some vehicle applications, the MAP replaces barometric pressure and is measured in similar increments.

The turbocharger/supercharger boost pressure sensor (designated A) will likely be of a similar design to the MAP sensor. It monitors the air density (boost pressure) inside the turbocharger/supercharger intake pipe and provides the PCM with an appropriate voltage signal.

A P023D code will be stored and a malfunction indicator lamp (MIL) may be illuminated if the PCM detects voltage signals between the MAP sensor and the turbocharger/supercharger boost pressure sensor A that differ by more than a programmed degree. Multiple ignition cycles (with a failure) may be required for MIL illumination.
How severe is this DTC?

Overall engine performance and fuel economy can be affected by the conditions contributing to a P023D code. It should be classified as severe.
What are some of the symptoms of the code?

Symptoms of a P023D trouble code may include:

Decreased engine performance
Excessively rich or lean exhaust
Delayed engine start (especially when cold)
Reduced fuel economy

What are some of the common causes of the code?

Causes

of this P023D trouble code may include:

Faulty MAP / turbocharger / supercharger boost pressure sensor A
Open or shorted MAP or turbocharger / supercharger boost pressure sensor A wiring or connector
Engine malfunction (insufficient vacuum production)
Restricted intercooler
PCM programming error or PCM fault

What are the P023D troubleshooting steps?

I would first want access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), a manual vacuum pressure gauge, and a reliable vehicle information source before attempting to diagnose a P023D code. Diagnosing any MAP sensor-related code should include verifying that the engine is producing sufficient vacuum. This can be done using the vacuum pressure gauge.

A visual inspection of all wiring and connectors for the MAP / turbocharger / supercharger boost pressure sensor system is necessary if there is no intercooler obstruction and the air filter is relatively clean. Perform necessary repairs. Then, I would connect the scanner to the vehicle’s diagnostic port and retrieve all stored codes and freeze frame data. Freeze frame data could be described as a snapshot of the exact circumstances occurring at the time of the malfunction that led to the stored P023D code. I like to note this information as it may be helpful as the diagnosis progresses. Now, clear the codes and test drive the vehicle to see if the code resets.

If it does:

Test the individual MAP / turbocharger / supercharger boost pressure sensors using the DVOM and your vehicle information source
Set the DVOM to the ohms setting and test the sensors when they are disconnected
Consult your vehicle information source for component testing specifications
MAP / turbocharger / supercharger boost pressure sensors that do not meet manufacturer specifications must be replaced

If all sensors meet manufacturer specifications:

Test the reference voltage (usually 5 volts) and a ground at the sensor connectors
Use the DVOM and connect the positive test lead to the reference voltage pin of the sensor connector with the negative test lead connected to the ground pin of the connector

If you find reference voltage and ground:

Reconnect the sensor and test the sensor signal circuit with the engine running
Follow the temperature to voltage chart found in the vehicle information source to determine if the respective sensors are functioning correctly
Sensors that do not reflect the specified voltage degree (according to manifold absolute pressure and turbocharger/supercharger boost pressure) specified by the manufacturer must be replaced

If the sensor signal circuit reflects the correct voltage degree:

Test the signal circuit (for the sensor in question) at the PCM connector. If there is a sensor signal at the sensor connector and none at the PCM connector, there is an open circuit between the two components
Test the individual system circuits using the DVOM. Disconnect the PCM (and any associated controllers) and follow the diagnostic flowchart or connector pin diagrams to test the resistance and/or continuity of the individual circuit

Suspect PCM fault or PCM programming error if all MAP / turbocharger / supercharger boost pressure sensors and circuits meet specifications.

Consult Technical Service Bulletins (TSBs) for assistance with your diagnosis
The turbocharger/supercharger boost pressure sensor is often left disconnected after air filter replacement and other related maintenance operations

P023E MAP – Turbo/Supercharger Boost Sensor ‘B’ Correlation

What does it mean?

This is a generic powertrain diagnostic trouble code (DTC) that generally applies to OBD-II vehicles. This may include, but is not limited to, Land Rover (Range Rover, Discovery), Ford, Chevrolet, Mazda, Dodge, Peugeot, Saab, Toyota vehicles, etc.

Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

 

If your OBD-II equipped vehicle has stored a P023E code, it means the powertrain control module (PCM) has detected a discrepancy in the correlation signals between the manifold absolute pressure (MAP) sensor and the turbocharger/supercharger boost sensor that has been designated “B”.

The “B” designates a specific boost sensor in a system that may use multiple boost sensors at different locations. Consult a reliable vehicle information source to accurately determine which sensor the B references (for the vehicle in question). This code applies only to vehicles equipped with forced air induction devices. Forced air induction devices include turbochargers and superchargers.

The MAP sensor provides the PCM with a voltage signal that reflects the density or pressure of the air in the intake manifold. The voltage signal is received (by the PCM) as kilopascal (kPa) units or inches of mercury (Hg). In some vehicle applications, the MAP replaces barometric pressure and is measured in similar increments.

The turbocharger/supercharger boost pressure sensor (designated B) will likely be of a similar design to the MAP sensor. It monitors the air density (boost pressure) inside the turbocharger/supercharger intake pipe and provides the PCM with an appropriate voltage signal.

A P023E code will be stored and a malfunction indicator lamp (MIL) may be illuminated if the PCM detects voltage signals between the MAP sensor and the turbocharger/supercharger boost sensor B that differ by more than a programmed degree. Multiple ignition cycles (with a failure) may be required for MIL illumination.
How severe is this DTC?

Overall engine performance and fuel economy may be affected by the conditions contributing to a P023E code. It should be classified as severe.
What are some of the symptoms of the code?

Symptoms of a P023E trouble code may include:

Decreased engine performance
Excessively rich or lean exhaust
Delayed engine starting (especially when cold)
Reduced fuel economy

What are some of the common causes of the code?

Causes

of this P023E trouble code may include:

Faulty MAP / turbocharger / supercharger boost sensor B
Open / shorted wiring or connector MAP / turbocharger / supercharger boost B
Engine mechanical failure (insufficient vacuum production)
Restricted intercooler
PCM programming error or PCM failure

What are the P023E troubleshooting steps?

I would first want access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), a manual vacuum gauge, and a reliable vehicle information source before attempting to diagnose a P023E code. Diagnosing any MAP sensor-related code should include verifying that the engine is producing sufficient vacuum. This can be done using the vacuum gauge.

A visual inspection of all wiring and connectors for the MAP / turbocharger / supercharger boost sensor system is necessary if there is no intercooler obstruction and the air filter is relatively clean. Perform necessary repairs. Then, I would connect the scanner to the vehicle’s diagnostic port and retrieve all stored codes and freeze frame data. Freeze frame data could be described as a snapshot of the exact circumstances occurring at the time of the malfunction that led to the stored P023E code. I like to note this information as it may be helpful as the diagnosis progresses. Now, clear the codes and test drive the vehicle to see if the code resets.

If it is:

Test the individual MAP / turbocharger / supercharger boost pressure sensors using the DVOM and your vehicle information source
Set the DVOM to the ohms setting and test the sensors when they are disconnected
Consult your vehicle information source for component testing specifications
MAP / turbocharger / supercharger boost sensors that do not meet manufacturer specifications must be replaced

If all sensors meet manufacturer specifications:

Test the reference voltage (usually 5 volts) and a ground at the sensor connectors
Use the DVOM and connect the positive test lead to the reference voltage pin of the sensor connector with the negative test lead connected to the ground pin of the connector

If you find reference voltage and ground:

Reconnect the sensor and test the sensor signal circuit with the engine running
Follow the voltage to temperature chart found in the vehicle information source to determine if the respective sensors are functioning correctly
Sensors that do not reflect the specified voltage degree (according to manifold absolute pressure and turbocharger/supercharger boost pressure) specified by the manufacturer must be replaced

If the sensor signal circuit reflects the correct voltage degree:

Test the signal circuit (for the sensor in question) at the PCM connector. If there is a sensor signal at the sensor connector and none at the PCM connector, there is an open circuit between the two components
Test the individual system circuits using the DVOM. Disconnect the PCM (and any associated controllers) and follow the diagnostic flowchart or connector pinout diagrams to test the resistance and/or continuity of the individual circuit

Suspect PCM failure or PCM programming error if all MAP / turbocharger / supercharger boost pressure sensors and circuits meet specifications.

Consult Technical Service Bulletins (TSBs) for assistance with your diagnosis
The turbocharger / supercharger boost sensor is often left unplugged after air filter replacement and other related maintenance operations

P023F Secondary Fuel Pump Circuit Open

What does it mean?

This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles. Although generic, specific repair steps may vary by make/model.

The fuel pump is powered by the fuel pump relay. When the PCM (Powertrain Control Module) activates the fuel pump relay, voltage is supplied to the fuel pump and it pressurizes the fuel system. Some vehicles have a feedback circuit on the fuel pump voltage supply circuit. This is simply a circuit spliced into the fuel pump voltage supply. The splice is typically located near the PCM.

The PCM monitors this feedback circuit to ensure the correct voltage is being sent to the fuel pump. By activating the fuel pump relay, it expects to see battery voltage on the feedback circuit. If the PCM sees an open condition with the signal when the fuel pump is not activated, P023F may set.

Symptoms

Symptoms of a P023F DTC may include:

MIL (Malfunction Indicator Lamp) illumination
Fuel pump runs without the key
Small amount of voltage present on the FP (Fuel Pump) voltage supply circuit due to a short circuit

Causes

Potential causes of a P023F code include:

Faulty fuel pump relay
Short to voltage on the FP voltage supply circuit or the feedback circuit
Short to ground at the PCM
PCM FP relay control circuit
FP relay control driver shorted to ground internally

Possible Solutions

It is possible with a P023F that the fuel pump runs continuously, even with the ignition off. If this is the case and you can hear the fuel pump running, you may be able to skip some of the following checks. Turn the key to KOEO (Key On Engine Off) and wait a few seconds. This allows the PCM to complete its fuel pump pre-cycle. Now, using your scan tool (if you have one), observe the FP VOLTAGE FEEDBACK reading in the data stream. This reading indicates the type of voltage the fuel pump is receiving.

If you do not have access to a scan tool, use a voltmeter to read the FP voltage at the fuel tank. If your reading indicates any voltage present at the fuel pump with KOEO (or if you can hear the pump running), remove the FP relay. If the voltage remains or the fuel pump continues to run, there is a short to voltage on the FP voltage supply circuit or the feedback circuit. Repair as necessary. If the voltage goes away (or the pump stops running) with the FP relay removed, try replacing the relay with a spare relay. When reinstalling the spare relay, if the voltage goes away, the relay was faulty due to a short. If, however, after replacement the relay voltage is still present, suspect that the PCM FP relay control circuit is shorted to ground.

Check for a short to ground on the PCM FP relay control circuit (ground driver) by removing the FP relay and ohming between a good ground and the PCM FP relay control. There should be no continuity to ground with KOEO (once the FP pre-cycle is complete). If there is continuity to ground, the wire is shorted. Locate the short to ground and repair as necessary. If you find no physical short, it may be necessary to cut the FP relay control wire near the PCM connector where it will be easy to repair and check for continuity to ground with KOEO coming from the PCM. If there is no continuity, the wire is shorted in the harness. But if there is continuity, the driver may be shorted internally and the PCM may require replacement.

P0240 Turbocharger Boost Sensor B Range/Performance

What does it mean?

This DTC is a generic powertrain code that applies to all turbocharged or supercharged vehicles.

The Powertrain Control Module (PCM) controls and monitors both the boost pressure and if the measured pressure is higher than the commanded pressure, DTC P0240 will be set and the PCM will illuminate the Check Engine light. To diagnose this code, you need to have a general understanding of three things:

What is boost pressure?
How is it controlled?
How is it measured?

In a normally aspirated engine (i.e., non-turbo), the downward movement of the pistons, called the intake stroke, creates a vacuum in the intake manifold in the same way a syringe draws in liquid. This vacuum is how the air/fuel mixture is drawn into the combustion chamber. A turbocharger is a pump driven by exhaust gases as they exit the combustion chamber. This creates pressure in the intake manifold. So, instead of the engine having to “suck” in the air/fuel mixture, it is instead force-fed a larger volume. In essence, there is already compression before the piston begins its compression stroke, which increases compression and thus increases power. This is boost pressure.

Boost pressure is controlled by the amount of exhaust gas allowed to pass through the turbo. The higher the amount, the faster the turbo spins, the higher the boost pressure. Exhaust gases are routed around the turbo via a bypass known as a wastegate. The PCM controls the boost pressure by regulating the opening of the bypass. It does this by opening or closing the wastegate as needed. This is accomplished by means of a vacuum motor mounted on or near the turbo. The PCM controls the amount of vacuum going to the vacuum motor via a control solenoid.

The actual pressure in the intake manifold is measured either by a boost pressure sensor (Ford/VW) or a manifold absolute pressure sensor (Chrysler/GM). The different sensor types represent the different technical description given by each manufacturer, but both perform the same function.

This particular code should be addressed as soon as possible due to the increased risk of overboost and damage to the catalyst.

Symptoms

When the conditions for setting P0240 are present, the PCM ignores the actual manifold pressure readings and uses an assumed or presumed manifold pressure, limits the amount of fuel and dynamic injection timing allowed. The PCM enters what is called Failure Mode Engine Management (FMEM) and is most noticeably characterized by a lack of power.

Causes

Causes

possible causes for setting this code are as follows:

Vacuum supply
Pinched, collapsed, or broken vacuum lines
Faulty control solenoid
Faulty PCM

Diagnostic and Repair Procedures

A good starting point is always to check the Technical Service Bulletins (TSBs) for your particular vehicle. Your problem may be a known issue with a known fix published by the manufacturer and can save you time and money when diagnosing.

Visually inspect vacuum lines for kinks, pinches, cracks, or breaks. Check all lines, not just those related to “B” wastegate control. A significant leak anywhere in the vacuum system can lead to poor performance of the entire system. If this checks out, proceed to step 2.
Using a vacuum gauge, check the vacuum on the inlet side of the “B” control solenoid. If none is present, suspect a faulty vacuum pump. If vacuum is present, proceed to step 3.
The control solenoid is actuated by pulse width modulation or duty cycle. Using a digital volt ohmmeter, which has a duty cycle or frequency setting, probe the signal wire at the solenoid connector. Drive the vehicle and check that a signal appears on the DVOM. If the signal is present, suspect a faulty control solenoid. If no signal is present, suspect a faulty PCM.

P0241 Turbocharger/Supercharger Boost Sensor B Circuit Low

What does it mean?

This is a generic powertrain diagnostic trouble code (DTC) applicable to all turbocharged or supercharged vehicles. Brands may include, but are not limited to, Audi, Nissan, Mitsubishi, Mazda, VW, etc.

 

The Powertrain Control Module (PCM) monitors boost pressure with a sensor called the Manifold Absolute Pressure (MAP) sensor. Understanding how a MAP sensor works is the first step in explaining the cause of P0241.

The PCM sends a 5-volt reference signal to the MAP sensor, and the MAP sensor returns a variable voltage signal to the PCM. When boost pressure is high, the voltage signal is high. When boost pressure is low, the voltage is low. The PCM uses the boost control solenoid to control the amount of boost pressure produced by the turbocharger while using the boost pressure sensor to verify that the boost pressure is correct.

This code is set when the PCM detects a low voltage signal indicating low boost pressure when a high-pressure command has been sent to the “B” boost control solenoid.

Symptoms

Symptoms of a P0241 code may include:

    Check Engine Light will be illuminated
    Low engine power
    Reduced fuel economy

Due to the increased risk of damage to the catalytic converter and turbo overboost when P0241 is present, it should be repaired before continuing to use the vehicle.

Causes

Causes

Possible causes for this code being set are:

    Faulty “B” boost sensor
    Faulty turbocharger
    Faulty PCM
    Wiring issue

Diagnostic and Repair Procedures

Before diagnosing P0241, ensure no other fault codes are present in the PCM’s memory. If there are other DTCs present, they should be checked first. Any codes related to wastegate control or the 5-volt reference will induce the conditions necessary to set this code. In my experience, the PCM is the least likely cause of this issue. More often than not, it is chafed or burned wires near the turbocharger causing shorts or opens in the circuit.

A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your problem may be a known issue with a known fix published by the manufacturer and can save you time and money during diagnosis.

    A thorough visual inspection is crucial when trying to resolve this particular DTC. I have seen faulty connections or defective wiring be the root of the problem more than anything else. Disconnect the connectors from the “B” boost sensor and the “B” boost control solenoid and carefully inspect the contact terminals (the metal parts inside the plastic plug) for signs of corrosion. Use a silicone dielectric compound on all connections when reassembling.
    Turn the ignition key with the engine off (KOEO), probe the boost sensor reference wire at the sensor connector with a digital voltmeter (DVOM) for a 5-volt check. If the voltage is correct, the boost sensor signal wire should read between 0.2 volts and 0.5 volts. If it is correct, proceed to the next step; if not, suspect a faulty boost sensor.
    Leave the DVOM connected and start the engine, and using a hand vacuum pump, apply vacuum to the turbocharger wastegate actuator. The voltage should increase; if it does, suspect a faulty PCM; if not, suspect a faulty turbocharger.