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

The fuel pump is activated by a relay controlled by the PCM. As its name suggests, a “relay” allows transmission of higher current to the fuel pump without that current having to pass through the PCM (Powertrain Control Module).

For obvious reasons, it’s preferable not to have higher current near the PCM. Higher current generates more heat and in case of failure, can cause PCM failure. This principle applies to any relay. Higher currents are kept under the hood, away from sensitive areas.

The relay essentially contains two sides. The “control” side which is essentially a coil and the “switch” side which is a set of electrical contacts. The control side (or coil side) is the low amp side. It’s powered by a switched ignition supply (12 volts with key on) and a ground. The ground circuit is activated by the PCM driver when needed. When the PCM fuel pump driver activates the relay coil, the coil acts as an electromagnet that closes the electrical contacts, completing the fuel pump circuit. This closed switch allows voltage to flow through the fuel pump activation circuit, activating the pump. Whenever the key is turned on, the PCM grounds the fuel pump circuit for a few seconds, activating the fuel pump and pressurizing the system. The fuel pump won’t be reactivated until the PCM sees an RPM signal.

The driver in the PCM is monitored for faults. When activated, the voltage of the drive or ground circuit should be low. When deactivated, the potential driver/ground voltage should be high or near battery voltage. If the PCM sees a voltage other than expected, P0230 may be set.

Symptoms

Symptoms of a P0230 DTC may include:

MIL illumination (malfunction indicator light)
No start condition
No fuel pump operation
Fuel pump runs continuously with ignition on

Causes

Potential causes of a P0230 code include:

Short to ground on control circuit
Open fuel pump control circuit
Short to battery voltage on control circuit
Harness chafing causing any of the above conditions
Faulty relay
Faulty PCM

Possible Solutions

Command the fuel pump on and off using a scan tool or simply by turning the ignition key on and off without starting the engine. If the fuel pump activates and deactivates, start the vehicle and measure current on the control circuit (ground) for a few minutes. It should be less than one amp and remain below one amp.

If not, replacing the relay is a good idea at this point. If the fuel pump doesn’t activate and deactivate, remove the relay and visually check for heat discoloration or loose terminals. If okay, install a test light between the ignition circuit supply and the ground driver terminals (if unsure, don’t attempt).

The test light should illuminate when the key is turned on or the fuel pump is activated. If not, ensure there’s voltage on one side of the coil (switched ignition supply). If voltage is present, repair the open or shorted circuit on the control ground circuit.

This diagnostic code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. 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 on the fuel pump power 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 sent to the fuel pump. By activating the fuel pump relay, it expects to see battery voltage on the feedback circuit. If the PCM detects unexpected high voltage when the fuel pump is not activated, P0232 may set.

Symptoms

Symptoms of a P0232 DTC may include:

    MIL (Malfunction Indicator Light) illumination
    Fuel pump running 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 P0232 code include:

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

Possible Solutions

With a P0232, it is possible for the fuel pump to run 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 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 if the fuel pump continues to run, there is a short to voltage on the FP voltage supply circuit or on the feedback circuit. Repair as necessary. If the voltage disappears (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 disappears, the relay was faulty due to a short circuit. 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. Find 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.

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

The P0234 fault code indicates that the Powertrain Control Module (PCM) detects a dangerously high boost pressure from the engine’s forced induction system. Boost levels exceeding recommended levels can compromise the structural integrity of the engine.

Normally, an engine relies on the vacuum produced by the downward movement of the piston to draw the air and fuel charge into the engine. A supercharger or turbocharger is an air compressor used to increase the air and fuel charge entering the engine. This is known as “forced induction” which allows a much smaller, fuel-efficient engine to produce the power normally available with a much larger engine.

The mechanical device used in forced induction is divided into three categories: positive displacement (roots style), centrifugal, and turbo. Roots style and centrifugal chargers are belt-driven while the turbo relies on exhaust pressure to operate.

A positive displacement supercharger is positioned on top of the intake. A centrifugal one looks much like a rotary air conditioning compressor and is located on the driver’s side of the engine. Turbochargers are located in line with the exhaust system.

As boost pressure increases, the pressure on the engine also increases. Your engine has recommended boost pressure limits to avoid the possibility of engine component failure. The P0234 code is set when these limits are exceeded and should be corrected as soon as possible to avoid damaging the engine or transmission.

Turbochargers rely on exhaust pressure to spin the turbine blades fast enough to produce air pressure above atmospheric pressure. However, they have an inherent lag where the exhaust pressure is insufficient to spin the turbo fast enough to create pressure. Depending on the type of unit used, the turbo needs 1,700 to 2,500 RPM before it starts to “spool up.”

Turbos spin around 250,000 RPM at full acceleration. Boost pressure increases with engine RPM. To regulate boost pressure and avoid overboost, a wastegate is installed. Most modern turbos have an internal wastegate and an external actuator. There is a rod from the actuator to the wastegate on the turbo. Air pressure from the intake manifold passes to the top of the wastegate. When boost pressure increases, it begins to exert force on the actuator spring which holds the wastegate closed. The higher the pressure, the more it overcomes the spring, causing the wastegate to open and divert exhaust gases away from the turbo blades, preventing further boost increase.

Regulating the pressure applied to the wastegate controls boost levels at a specific RPM. To do this, the computer uses barometric or MAP sensors, engine and transmission temperature sensors, knock sensors, and intake pressure sensors to determine how much wastegate opening is needed to provide the best boost levels.

To regulate boost levels, the computer uses either a solenoid, a stepper motor, or a pulse modulator. By regulating the pressure to the wastegate actuator, various degrees of boost are possible.

Symptoms

The symptoms displayed for a P0234 code depend on the cause of the overboost condition:

    The Service Engine Soon or Check Engine light will illuminate.
    You will experience a loss of power.
    The engine may show signs of overheating.
    The transmission may show signs of overheating and harsh shifting.
    Additional codes associated with the condition defined by P0234 may be present to help identify the cause. Codes are available for all electrical components used by the engine management computer for boost level control.
    The engine may show signs of pre-ignition in the form of knocking.
    The engine may display misfires.

Causes

Potential causes of this DTC include:

    In the absence of other fault codes associated with the overboost condition, it would be safe to say the problem is mechanical. The operation of the wastegate is the most likely.
    The wastegate is either stuck closed, causing the turbo to spin higher than normal, thus causing overboost.
    The rod from the wastegate actuator to the wastegate on the turbo is bent.
    A hose has come off the wastegate or the boost controller.
    A supply line to the boost controller or from the controller to the wastegate is clogged.
    Dodge trucks with a Cummins diesel have a particular issue. They run fine, but the Check Engine light comes on and sets the P0234 code at idle, but the light goes out several minutes later at cruising speed. The digital boost control gauge is connected to the MAP sensor which has an intermittent fault at idle but does not set a code. Replacing the MAP sensor fixes this.

This is a generic powertrain diagnostic trouble code (DTC) applicable to all turbocharged vehicles. Vehicle brands may include, but are not limited to, VW, Dodge, Mercedes, Isuzu, Chrysler, Jeep, 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 P0237.

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 “A” boost control solenoid.

Symptoms

Symptoms of a P0237 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 P0237 is present, it should be repaired before continuing to use the vehicle.

Causes

Causes

Possible causes for this code being set are as follows:

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

Diagnostic and Repair Procedures

Before diagnosing P0237, 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 burnt 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 faulty wiring be the root of the problem more than anything else. Disconnect the connectors for the “A” boost sensor and the “A” boost control solenoid and carefully inspect the contact terminals (the metal parts inside the plastic plug) for signs of spreading. Use a silicone dielectric compound on all connections during reassembly.
    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 be 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 vacuum motor. The voltage should increase; if it does, suspect a faulty PCM; if not, suspect a faulty turbocharger.

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.

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.