P0497 Evaporative Emission System Low Purge Flow

What does it mean?

This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to all vehicles from 1996 onwards (Ford, Honda, Mazda, Mercedes, VW, etc.). Although generic, specific repair steps may vary by make/model.

When I see that a P0497 code has been stored, I know that the Powertrain Control Module (PCM) has detected a low flow condition in the Evaporative Emission (EVAP) purge system.

Designed to capture fuel vapors (from the fuel tank) before they escape into the atmosphere, the EVAP system uses a sealed canister to store excess vapors until the engine is ready to burn them. Fuel vapors are routed to the canister (often called the charcoal canister) via a specially designed valve and a network of metal tubes and rubber hoses. The pressure that builds up when fuel is stored causes the vapors to escape into the tubes and eventually into the canister. The canister contains a charcoal element that absorbs the fuel vapors for release at the appropriate time.

The purge control solenoid is activated when the PCM determines that the engine is in a condition to efficiently burn the EVAP fuel vapors. An EVAP pressure sensor is used to monitor the effectiveness of the EVAP system.

The P0497 code is related to the EVAP purge valve. The purge control solenoid/valve is typically located in the engine compartment. A constant intake vacuum supply hose (from the engine intake manifold) is attached to one opening on the purge control valve, with a second line connected to the only other opening. In most cases, a constant battery voltage supply is present at one terminal of the purge control valve, and the PCM provides a ground pulse when driving conditions are optimal. This allows the valve to open and admit vacuum to reach the canister. When vacuum reaches the canister, ambient air is drawn through the charcoal element, releasing the stored fuel vapors. The engine vacuum draws the fuel vapors into the intake manifold where they are burned with conventional fuel.

In some systems, if there is not a sufficient change in intake manifold air pressure or exhaust oxygen content when the purge control solenoid/valve is opened, a P0497 will be stored and a malfunction indicator lamp may soon illuminate. Other systems use an EVAP pressure sensor to monitor and control the operation of the purge and vent control solenoids. In this type of system, if the EVAP pressure does not drop sufficiently when the purge control valve is opened, a code will be stored and the malfunction indicator lamp will soon illuminate.

Symptoms

and Severity

This is an emissions-related code. While it may slightly reduce fuel efficiency, there is no inherent danger. Symptoms of a P0497 code may include:

Slightly decreased fuel efficiency
Noise from a vacuum leak in the area under the hood
Poor engine idle quality
In most cases, no symptoms will be apparent

Causes

Possible causes for setting this code are:

Faulty EVAP pressure sensor
Faulty EVAP purge solenoid/valve
Restricted EVAP canister element
Short circuit or open circuit (wiring or connector) for the EVAP purge control solenoid/valve
Cracked, pinched, or collapsed vacuum lines/hoses

Diagnostic and Repair Procedures

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 suitable diagnostic scanner, a digital volt/ohmmeter, a manufacturer’s service manual (or equivalent), and a smoke machine will help diagnose the P0497 code.

I usually start my diagnosis with a visual inspection of all system wiring and connectors, as well as vacuum lines and hoses. Repair or replace any damaged wiring and/or connectors as needed.

The EVAP system consists of a network of long vacuum lines and metal tubes, which can be a chore in itself. If you have access to a smoke machine, it can make this process much easier. Keep in mind that most of these vacuum circuits will have no vacuum unless the purge control solenoid/valve is activated. Repair or replace faulty vacuum lines and hoses as needed.

If charcoal is found in the vacuum lines, immediately suspect a faulty canister. Compromised charcoal elements usually cannot be replaced individually and will likely require a complete canister replacement. Connect the scanner to the diagnostic connector and retrieve all stored codes and freeze frame data. Write all of this down so you can refer back to it later. Clear all codes and test drive the vehicle. Remember that resetting this type of code may take several drive cycles. If it resets, continue your diagnosis.

Consult the service manual for specific system specifications and test the operation of the EVAP purge solenoid/valve. Use the scanner to activate the purge control solenoid and physically check for vacuum flow with the engine running when the purge control solenoid is activated.

If the solenoid does not open when activated, check the system voltage and ground signals against the manufacturer’s specifications. If voltage and ground signals are present, suspect a faulty solenoid. Test the purge control solenoid (with the DVOM) using the service manual as a guide. If voltage and ground signals are absent, disconnect the system controllers and test the system circuits with the DVOM. Repair or replace any open or shorted circuits as necessary.

If all system circuits and components meet the manufacturer’s specifications, suspect a faulty PCM or a PCM programming error.

Additional Diagnostic Notes:

Engines in poor condition may not provide sufficient vacuum for EVAP purge operation
A loose or missing fuel cap will not cause this code to be stored
To effectively use the smoke machine, remove the vacuum lines from the canister and plug them before applying smoke

P0498 Evaporative Emission System Purge Control Valve Circuit Low

Low Circuit Value for Evaporative Emission System Vent Valve Control

What Does It Mean?

The Powertrain Control Module (PCM) / Engine Management Computer (EMC) / Engine Control Module (ECM) has detected a malfunction in the circuit that controls the vent for vapor in the evaporative emission systems.

When fuel is in the tank, it emits fuel vapor, while the vent line opens and allows the vapors to flow into the engine intake manifold, a charcoal canister, or into the atmosphere, depending on the vehicle. This purge valve is part of the simple yet complicated evaporative emissions system.

Symptoms

Symptoms of a DTC P0498 will include the Malfunction Indicator Light (MIL) illuminating; you probably won’t notice any other symptoms.

Causes

Causes

Potential causes may include:

    Faulty vent valve
    Wire/circuit issue
    PCM/EMC/ECM fault

Possible Solutions

Here are some steps to follow to diagnose and repair this fault code:

Check your fuses; there may be a fuse that powers the vent solenoid.

Look for a chafed or rubbed wiring harness. Check both wires to see if they are shorted to each other, to ground, or to power.

Visually inspect the vent valve for cracks or damage.

Trace the wires to and from the PCM/EMC/ECM and check for continuity using a digital volt-ohmmeter (DVOM).

If you have access to an advanced-level scan tool, activate the valve while reading the power and ground at the connector or simply use a test light wired to both terminals; it will light up if the power and ground are OK.

Using a DVOM, check the resistance of the vent; in most cases, the resistance reading should be low; refer to the manufacturer’s specifications or compare it to a new one. A reading that is too low or too high indicates a faulty coil inside the valve, meaning a replacement is necessary. This code seems to be common on Dodge, Chrysler, and Jeep products. In these cases, the vent valve was faulty. With GM products (especially trucks), GM has released a new updated valve assembly.

Finally, remove the valve; you may be able to access the pivot inside, and it might just be sticking due to fuel residue. Clean it and retest.

Evaporative Emission System Vent Control Circuit High

High Value of the Evaporative Emission System Vent Valve Control Circuit

What Does It Mean?

This code 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 vary by model.

The Powertrain Control Module (PCM) / Engine Management Computer (EMC) / Engine Control Module (ECM) has detected a failure in the circuit that controls the vent for the vapor from the evaporative emission systems.

When fuel is in the tank, it emits fuel vapor, while the vent line opens and allows the vapors to flow into the engine intake manifold, a charcoal canister, or into the atmosphere, depending on the vehicle. This purge valve is part of the simple yet complicated evaporative emissions system.

Symptoms

Symptoms of a DTC P0499 include the illumination of the Malfunction Indicator Light (MIL); you will likely not notice any other symptoms.

Causes

Potential causes may include:

Faulty vent valve
Wiring/circuit issue
PCM/EMC/ECM fault

Possible Solutions

Here are some steps to follow to diagnose and repair this fault code:

Check your fuses; there may be a fuse that powers the vent solenoid.

Look for a chafed or rubbed wiring harness. Check both wires to see if they are shorted to each other, to ground, or to power.

Visually inspect the vent valve for cracks or damage.

Trace the wires to and from the PCM/EMC/ECM and check for continuity using a digital volt-ohm meter (DVOM).

If you have access to an advanced-level scan tool, actuate the valve while reading the power and ground at the connector or simply use a test light wired to both terminals; it will light up if the power and ground are OK.

Using a DVOM, check the resistance of the vent; in most cases, the resistance reading should be low—refer to the manufacturer’s specifications or compare it to a new one. A value that is too high or too low indicates a faulty coil inside the valve, meaning a replacement is necessary. This code appears to be widespread on Dodge, Chrysler, and Jeep products. In these cases, the vent valve was faulty. With GM products (especially trucks), GM has released an updated valve set.

Finally, remove the valve; you may be able to access the pivot inside, and it might simply be sticking due to fuel residue. Clean it and retest.

Exhaust Gas Recirculation Flow B

The code P049A refers to a problem in the exhaust gas recirculation (EGR) flow, specifically in the position of the EGR valve “B”. This means that the powertrain control module (PCM) has detected an insufficient or excessive flow of exhaust gases in the recirculation system, which disrupts the proper functioning of the EGR. This valve is crucial for reducing NOx (nitrogen oxide) emissions that are produced during fuel combustion in the engine.

🧑‍🔧 Code Details and Explanation

  • “B” refers to a specific position or a particular type of EGR valve in some engines (often a second valve or a specific configuration of the EGR valve).

  • This issue can result from a mechanical problem (such as a blockage or malfunction of the EGR valve) or an electrical problem (faulty sensors, damaged wiring).

The role of the EGR system is to reintroduce exhaust gases into the engine to reduce NOx emissions by lowering the combustion temperature.

🚨 Possible Symptoms

  • ⚠️ Decreased engine performance (loss of power, poor acceleration)

  • ⚡ Hard starting, especially when cold

  • ⛽ Reduced fuel efficiency

  • 🌫️ Abnormal exhaust (black smoke, odor)

  • 🛑 Check engine light on

🔧 Possible Causes of P049A

  1. Faulty EGR valve (blocked by carbon deposits, mechanically defective).

  2. Faulty sensors:

    • DPFE (EGR valve differential pressure sensor),

    • MAP (manifold absolute pressure sensor),

    • MAT (manifold air temperature sensor).

  3. Clogged EGR passages or cracked.

  4. Faulty electrical wiring (short circuit, corroded or damaged connectors).

  5. PCM problems (incorrect programming or failure).

🛠️ Troubleshooting Steps

  1. OBD-II scanner
    Use a diagnostic tool to confirm the code and check for other error codes.

  2. Visual inspection
    Check the condition of the connectors, wires, and EGR pipes. Ensure there are no cracks, corrosion, or dirt.

  3. EGR valve and sensors
    If the circuits and connectors are in good condition, test the EGR valve by manually activating the system via the scanner. Then check the EGR pressure sensor (DPFE) and other sensors like MAP or MAT using a multimeter.

  4. EGR valve cleaning
    If you find carbon deposits, clean the valve and passages using an EGR valve cleaner.

  5. PCM test
    If the problem persists after cleaning, perform a test of the PCM. If the PCM signal is absent or incorrect, you may have a programming error or a faulty PCM.

⚠️ Severity

The code P049A can be serious because it directly affects pollutant emissions and can lead to:

  • A loss of engine performance,

  • A high combustion rate with more pollution,

  • Failure in the technical inspection.

Therefore, it is advisable to resolve this issue quickly to avoid further damage to the engine and related systems (such as sensors and the DPF).

P049B Insufficient Exhaust Gas Recirculation B Flow Detected

The P049B code corresponds to an insufficient exhaust gas recirculation “B” flow detected, meaning that the PCM (Powertrain Control Module) does not observe the expected level of exhaust gases being reintroduced into the intake, despite the EGR valve being commanded open.

🧾 Simple Translation and Explanation

The EGR (Exhaust Gas Recirculation) system is designed to reintroduce a portion of the exhaust gases into the engine to reduce NOx emissions. The flow B generally refers to a second EGR valve, a secondary channel, or a specific position on a modulating valve.

When this flow is lower than expected, it results in:

  • Poor emission reduction,
  • Risk of combustion overheating,
  • Deactivation of certain systems (DPF regeneration, SCR, etc.).

🚨 Severity of the P049B Code

Serious, especially if the vehicle is diesel:

  • 📉 Loss of power,
  • ⛽ Increased fuel consumption,
  • 🌫️ Excessive smoke,
  • ❗ Failure in pollution control inspection.

🔍 Possible Symptoms

  • Engine light on (MIL)
  • Irregular idle or rough running
  • Hard starting (especially when cold)
  • Black smoke or exhaust odor
  • Loss of torque at low RPM

🔧 Common Causes of P049B

Component Common Issue
EGR Valve Stuck closed (due to soot)
EGR Channels Clogged (carbon)
DPFE / MAP / MAT Sensor Clogged or faulty
EGR / DPFE Hoses Cracked, broken, or disconnected
Wiring / Connectors Short circuit, melted wire, corrosion
PCM Rare, but possible (bug or failure)

🛠️ Recommended Troubleshooting Steps

  1. OBD-II Scan
    ➤ Check if other codes are present (especially P0401, P0405, etc.).
  2. Visual Inspection
    ➤ Check the EGR wiring, related sensors, and flexible hoses.
    ➤ Look for signs of soot, cracks, burns, or damaged connectors.
  3. EGR Valve Test (with diagnostic tool or manually)
    ➤ Try to activate it remotely (with a compatible diagnostic tool).
    ➤ If it doesn’t move or is stuck, remove and clean it.
  4. Sensor Cleaning or Replacement
    ➤ Especially DPFE (differential pressure), MAP, or intake air temperature sensor.
    ➤ Check the expected voltage (using a DVOM) and compare to manufacturer specifications.
  5. Continuity Test (DVOM)
    ➤ If the sensors and valve are correct, check the circuits up to the PCM.
  6. Manual Cleaning of the EGR Valve and Passages
    ➤ In case of severe clogging, soot/carbon deposits to clean with a wire brush or EGR cleaner.

✅ Conclusion

The P049B code is generally caused by a stuck or clogged EGR valve, or by an error in flow detection by the associated sensors. Prompt intervention is recommended to avoid damage or deactivation of other systems (such as the DPF).

Excessive Exhaust Gas Recirculation B Flow Detected

Understanding Error Code P049C: Excessive Flow Detected in EGR System “B”

Introduction

  • What does the P049C code mean? (General definition: the PCM has detected excessive flow in the “B” circuit of the EGR system for a specific downgrade setting).
  • This is a generic powertrain diagnostic trouble code (DTC) applicable to OBD-II equipped vehicles with an Exhaust Gas Recirculation (EGR) system.
  • Examples of affected brands: Dodge, Ford, Toyota, Chevrolet, Nissan, VW, Audi, Mazda, Mitsubishi, Subaru, etc.
  • Important: Precise repair steps may vary depending on the year, make, model, and powertrain configuration.
  • The “B” designation refers to a specific position of the EGR valve in the downgraded state.
  • An electrical or mechanical problem can cause the P049C code to be stored.

Downgraded EGR System Operation and Importance

  • The downgraded EGR valve system is essential for reducing nitrogen oxide (NOx) emissions produced by the internal combustion of diesel engines.
  • NOx contributes to the depletion of the ozone layer.
  • NOx emissions are regulated by federal mandates in North America.
  • The downgraded EGR system recirculates a portion of the exhaust gases to the intake manifold in measured increments for a second combustion.

EGR Flow Monitoring

  • EGR system flow is monitored by different methods:
    • DPFE Sensor (Differential Pressure Feedback EGR): Measures pressure in the tube connecting the EGR valve and the exhaust manifold. Valve opening increases pressure and sensor voltage.
    • MAP Sensor (Manifold Absolute Pressure): In some applications, a proportional change in MAP sensor voltage is expected when the PCM commands the downgraded EGR to open to a certain level.
    • MAT Sensor (Manifold Air Temperature): Some vehicles use the MAT sensor to detect the temperature increase when hot exhaust gases recirculate into the intake manifold.
  • The P049C code is stored and the Malfunction Indicator Lamp (MIL) may illuminate if the PCM does not detect the expected change from the “B” EGR flow monitoring sensor system, indicating an excessively high flow.
  • Several ignition cycles with the fault may be required for the MIL to illuminate on some vehicles.

Severity of DTC P049C

  • Conditions contributing to a P049C code can affect overall engine performance and fuel efficiency.
  • This code should be classified as severe.

Possible Symptoms of Code P049C

  • List of associated symptoms:
    • Decreased engine performance
    • Excessively rich or lean exhaust
    • Delayed engine starting (especially when cold)
    • Reduced fuel efficiency

Common Causes of Code P049C

  • List of possible causes:
    • Faulty EGR valve
    • EGR passage(s) clogged with carbon deposits
    • Collapsed or cracked DPFE hoses
    • Faulty DPFE, MAP, or MAT sensor
    • Open or shorted circuits to the EGR valve or associated sensors

P049C Troubleshooting Steps

  • Step 1: Retrieving codes and freeze frame data:
    • Start by locating the vehicle’s diagnostic connector and use a scanner to retrieve all stored codes.
    • Note this information for future reference.
    • Test drive the vehicle to see if the P049C code resets immediately.
  • Step 2: Consulting Technical Service Bulletins (TSBs):
    • Search the vehicle’s TSBs for entries matching the vehicle, stored codes, and symptoms. TSBs may contain helpful diagnostic tips from specialists.
  • Step 3: Preparing tools and information:
    • If the P049C code is stored after clearing, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information (wiring diagrams, component specifications).
  • Step 4: Visual inspection:
    • Visually inspect the EGR valve, all associated wiring, and connectors.
    • Pay close attention to wiring harnesses located near hot exhaust manifolds and the sharp edges of heat shields.
  • Step 5: Precautions before electrical testing:
    • To avoid damaging control modules, disconnect all associated control modules from the circuit before testing resistance or continuity with the DVOM.
  • Step 6: Testing manual activation of the EGR system:
    • Use the scanner to manually activate the EGR system (note that most systems require a certain speed for automatic activation).
  • Step 7: Testing EGR valve circuits:
    • Using wiring diagrams and connector pinout charts (from your information source), test each circuit of the EGR valve connector with the DVOM.
    • Circuits not matching manufacturer specifications must be traced back to their source (usually the PCM connector) and retested.
    • If no PCM output signal is detected, suspect a PCM programming issue or a faulty PCM.
    • Repair or replace open or shorted circuits as necessary.
  • Step 8: Testing the EGR valve and associated sensors:
    • If all circuits meet specifications, use the DVOM to test the EGR valve itself and the associated sensors (DPFE, MAP, MAT).
    • Your vehicle information source will provide the testing procedures and specifications for these components.
    • Replace the downgraded EGR valve and/or associated sensors if they do not meet manufacturer specifications.
  • Important note: This code (P049C) should only appear on vehicles equipped with downgradable EGR valve systems.

P049D EGR A Control Position Exceeded Learning Limit

Exhaust Gas Recirculation A Control Position Exceeded Learning Limit

What does this mean?

This is a generic diagnostic trouble code (DTC) for the powertrain that generally applies to OBD-II equipped vehicles with an Exhaust Gas Recirculation (EGR) system. This may include, but is not limited to, vehicles from Dodge/Ram (Cummins), Chevy/GMC (Duramax), Honda, Jeep, Hyundai, 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 P049D code, it means the Powertrain Control Module (PCM) has detected a malfunction in a certain control position of the exhaust gas recirculation (EGR) valve. It referred to a specific position of the EGR valve.

The EGR valve system is designed to recirculate a portion of the spent exhaust gases back to the intake manifold, in measured increments, so it can be burned a second time. This process is essential in reducing nitrogen oxide (NOx) particles that are released into the atmosphere as a byproduct of internal combustion and diesel engine operation. NOx is suspected to be a contributing factor to the depletion of the ozone layer from exhaust emissions. NOx emissions are regulated by federal mandate in North American vehicles.

The learning limit is a programmed degree that reflects the minimum and maximum parameters to which a certain position (A) of the EGR valve can adapt. If the PCM detects that the actual EGR valve position is beyond these parameters, a P049D code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated. In some vehicle applications, multiple ignition cycles (with a fault) are required for the MIL to illuminate.
How severe is this DTC?

Since the P049D code pertains to the EGR system, it should not be considered severe.
What are some of the symptoms of the code?

Symptoms of a P049D fault code may include:

There will likely be no symptoms associated with this code
Slightly decreased fuel efficiency
Possible drivability issues

What are some of the common causes of the code?

Causes

of this P049D code may include:

Faulty EGR valve
Faulty EGR sensor
Incorrect PCM or PCM programming error

What are the troubleshooting steps for P049D?

I would typically begin my diagnosis by locating the vehicle’s diagnostic connector and retrieving all stored codes and associated data. I would write down all this information in case I need it as I proceed with my diagnosis. Then, I would test the vehicle to see if the code immediately resets.

By searching the vehicle’s Technical Service Bulletins (TSBs) for entries that match the vehicle, stored codes, and displayed symptoms, you may discover the solution to your (potentially difficult) diagnosis. Since TSB entries come from thousands of repair specialists, they often contain very helpful details.

If P049D is stored after clearing the codes, I would have access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.

Now, I would perform a visual inspection of the EGR valve and all associated wiring and connectors. Focus on wiring harnesses that are routed near hot exhaust components and the sharp edges often associated with heat shields.

NOTE: Disconnect all associated controllers from the circuit before testing resistance/continuity with the DVOM.

Using wiring diagrams and connector pinout charts, located in your vehicle information source, test each EGR valve connector circuit (with the DVOM) for the proper signal. It may be necessary to manually activate the EGR system using the scanner, as most systems require a defined vehicle speed before automatic activation can occur. Circuits that do not meet manufacturer specifications will need to be traced back to the source (usually the PCM connector) and retested. If the PCM output signal is not detected, suspect a PCM programming error or faulty PCM. Otherwise, repair or replace open/short-circuited circuits as needed.

Use the DVOM to test the actual EGR valve and integrated sensors if all circuits meet manufacturer specifications. Your vehicle information source will again provide information for testing this component. If the EGR valve and all (integrated) sensors do not align with manufacturer specifications, suspect it is faulty.

This code should only be displayed in vehicles equipped with an EGR valve.

P049E EGR B Control Position Exceeded Learning Limit

Exhaust Gas Recirculation B Position Control Learning Limit Exceeded

What does that mean?

This is a generic diagnostic trouble code (DTC) for the powertrain that generally applies to OBD-II vehicles equipped with an Exhaust Gas Recirculation (EGR) system. This may include, but is not limited to, vehicles from Dodge/Ram (Cummins), Chevy/GMC (Duramax), Honda, Jeep, Hyundai, 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 P049E code, it means the Powertrain Control Module (PCM) has detected a malfunction in a specific position control of the lowered Exhaust Gas Recirculation (EGR) valve. B refers to a specific position of the lowered EGR valve.

The lowered EGR valve system is designed to recirculate a portion of the spent exhaust gases back into the intake manifold, in measured increments, so it can be burned a second time. This process is essential in reducing nitrogen oxide (NOx) particles that are released into the atmosphere as a byproduct of internal combustion and diesel engine operation. NOx is suspected to be a contributing factor to the depletion of the ozone layer from exhaust emissions. NOx emissions are regulated by federal mandate in North American vehicles.

The learning limit is a programmed degree that reflects the minimum and maximum parameters to which a specific position (B) of the lowered EGR valve can adapt. If the PCM detects that the actual position of the EGR valve is beyond these parameters, a P049E code will be stored and a Malfunction Indicator Lamp (MIL) may illuminate. In some vehicle applications, multiple ignition cycles (with a fault) are required for the MIL to light up.
How severe is this DTC?

Since the P049E code relates to the EGR system, it should not be considered severe.
What are some of the symptoms of the code?

Symptoms of a P049E fault code may include:

There will likely be no symptoms associated with this code
Slightly decreased fuel efficiency
Possible driving issues

What are some common causes of the code?

Causes

of this P049E code may include:

Faulty EGR valve
Faulty EGR sensor
Incorrect PCM or PCM programming error

What are the troubleshooting steps for P049E?

I would typically start my diagnosis by locating the vehicle’s diagnostic connector and retrieving all stored codes and associated data. I would write down all this information in case I need it as I proceed with my diagnosis. Then, I would test the vehicle to see if the code resets immediately.

By searching the vehicle’s Technical Service Bulletins (TSBs) for entries matching the vehicle, stored codes, and displayed symptoms, you might discover the solution to your (potentially difficult) diagnosis. Since TSB entries come from thousands of repair specialists, they often contain very helpful details.

If the P049E is stored after clearing the codes, I would have access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.

Now, I would perform a visual inspection of the EGR valve and all associated wiring and connectors. Focus on wiring harnesses routed near hot exhaust components and the sharp edges often associated with exhaust shields.

NOTE: Disconnect all associated controllers from the circuit before testing resistance/continuity with the DVOM.

Using wiring diagrams and connector pinout charts, located in your vehicle information source, test each EGR valve connector circuit (with the DVOM) for the appropriate signal. It may be necessary to manually activate the EGR system using the scanner, as most systems require a defined speed before automatic activation can occur. Circuits that do not meet manufacturer specifications will need to be traced back to the source (usually the PCM connector) and retested. If the PCM output signal is not detected, suspect a PCM programming error or faulty PCM. Otherwise, repair or replace open/short-circuited circuits as needed.

Use the DVOM to test the actual EGR valve and integrated sensors if all circuits meet manufacturer specifications. Your vehicle information source will again provide information for testing this component. If the lowered EGR valve and all (integrated) sensors do not align with manufacturer specifications, suspect it is faulty.

This code should only appear in vehicles equipped with a lowered EGR valve.

Exhaust Pressure Control Valve B

What does it mean?

This generic powertrain/diagnostic engine code generally applies to diesel engines, including but not limited to certain Ford, Dodge, Mercedes, Nissan, and VW vehicles.

A valve is placed in the exhaust stream after the exhaust manifold to generate heat in the form of backpressure in the exhaust. This heat and/or backpressure can be used to assist with cold starting. It can also be used to oppose cylinder pressure from the engine cylinders to the exhaust, thereby slowing the engine and the vehicle with it. This is particularly useful during towing operations.

This code strictly pertains to the exhaust pressure control solenoid output circuit. This code is considered an electrical circuit fault only.

Troubleshooting steps may vary depending on the manufacturer, type of exhaust backpressure control, and the color of the control solenoid wires. Refer to a vehicle-specific repair manual to determine which is the “B” valve in your particular case.

Symptoms

Symptoms of a P049F engine code may include:

Malfunction Indicator Light (MIL) illuminated
Lack of power
Absence of engine braking
Longer than normal cold engine warm-up time

Potential Causes of P049F

Typically, the causes for this code to set are:

Short to power in the supply circuit between the exhaust pressure control solenoid and the PCM (Powertrain Control Module)
Open in the supply circuit between the exhaust pressure control solenoid and the PCM
Short to ground in the exhaust pressure control solenoid supply circuit
Faulty exhaust pressure control solenoid
Possibly a failed PCM (highly unlikely)

Diagnostic and Repair Procedures

A good starting point is always to search for a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogramming to address this issue, and it’s worth checking before discovering you’ve taken a long/wrong path.

Next, locate the “B” exhaust pressure control solenoid on your particular vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burns, or melted plastic. Separate the connectors and carefully inspect the terminals (the metal parts) inside the connectors. See if they appear corroded, burnt, or perhaps greenish compared to the normal metal color you’re used to seeing. You can get electrical contact cleaner at any auto parts store if terminal cleaning is needed. If that’s not possible, find 91% rubbing alcohol and a soft plastic-bristled brush to clean them. Then, let them air dry, get some dielectric silicone compound (the same used for bulb sockets and spark plug wires), and apply it where the terminals make contact.

If you have a scan tool, clear the diagnostic codes from memory and see if this code returns. If not, the connections were likely your problem.

If the code returns, we’ll need to test the solenoid and its associated circuits. Typically, there are 2 wires to the exhaust pressure control solenoid. First, disconnect the wiring harness from the exhaust pressure control solenoid. With a digital volt-ohm meter (DVOM), connect one meter lead to one terminal of the solenoid. Connect the remaining meter lead to the other terminal of the solenoid. It should not be open or shorted. Check the resistance specifications for your specific vehicle. If the solenoid is open or shorted (infinite resistance or no resistance/0 ohms), replace the solenoid.

If that’s okay, with a DVOM, check that the exhaust pressure control solenoid supply circuit has 12V (red lead to the solenoid supply circuit, black lead to a good ground). Ensure the ignition is on. If there is no 12 volts at the solenoid, or if there is 12 volts when the ignition is off, repair the wiring from the PCM or relay to the solenoid, or possibly a faulty PCM.

If that checks out, verify that the exhaust pressure control solenoid is properly grounded. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the exhaust pressure control solenoid circuit ground. If the test light does not illuminate, that would indicate a circuit problem. If it lights up, wiggle the wiring harness going to each sensor to see if the test light flickers, indicating an intermittent connection.

If all tests have passed so far and you continue to get a P049F code, it would most likely indicate a failing exhaust pressure control solenoid, although a faulty PCM cannot be ruled out until the solenoid has been replaced.

P04A0 Exhaust Pressure Regulator Valve B Range / Performance

Exhaust Pressure Control Valve “B” Range/Performance

What does it mean?

This generic powertrain/engine diagnostic code typically applies to diesel engines, including but not limited to certain Ford, Dodge, Mercedes, Nissan, and VW vehicles.

This code may also apply to trucks equipped with diesel engines and dealer-installed exhaust brakes.

A valve is placed in the exhaust stream after the exhaust manifold to generate heat in the form of backpressure in the exhaust. This heat and/or backpressure can be used to assist with cold starts. It can also be used to oppose cylinder pressure from the engine’s cylinders to the exhaust, thereby slowing the engine and the vehicle with it. This is particularly useful during towing operations.

This code is strictly concerned with the incoming signal from the exhaust pressure sensor that does not match the intake manifold pressure, ambient air pressure, or preprogrammed information during normal driving. It could be a mechanical or electrical circuit fault, depending on the vehicle manufacturer.

Troubleshooting steps may vary depending on the manufacturer, the type of exhaust backpressure control, and the color of the control solenoid wires. Refer to a vehicle-specific repair manual to determine which is the “B” valve in your particular case.

Symptoms

Symptoms of a P04A0 engine code may include:

Malfunction Indicator Lamp (MIL) illuminated
Lack of power
Absence of engine braking
Cold engine warm-up time longer than normal

Potential Causes of P04A0

Typically, the causes for this code to set are:

Stuck exhaust backpressure valve
Possibly stuck/damaged/misadjusted turbocharger deflector
Exhaust system restriction/leak
Exhaust gas pressure sensor
Possibly failed PCM (highly unlikely)

Diagnostic and Repair Procedures

A good starting point is always to search for a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogramming to address this issue, and it’s worth checking before discovering you’ve taken a long/wrong path. PCM = Powertrain Control Module.

Next, check for any exhaust leaks. Listen for exhaust noise from all manifolds and exhaust pipes and look for the presence of black soot at the leak location. If there is a leak, repair the exhaust leak first.

Then, locate the “B” exhaust pressure sensor on your specific vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, scraping, bare wires, burns, or melted plastic. Disconnect the connectors and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt, or perhaps greenish compared to the normal metal color you are probably used to seeing. You can get electrical contact cleaner at any auto parts store if terminal cleaning is needed. If that’s not possible, find 91% isopropyl alcohol and a soft plastic-bristled brush to clean them. Then, let them air dry, get some dielectric silicone compound (the same kind used for light bulb sockets and spark plug wires), and apply a small amount where the terminals make contact.

Additionally, if your vehicle is equipped, remove the sensing tube that connects the exhaust backpressure sensor to the exhaust manifold. Try blowing through it. If you cannot, this is also a possible cause of this code.

If you have a scan tool, clear the diagnostic codes from the memory and see if this code returns. If it does not, the connections were likely your problem.

If the code returns, you will need to check the proper operation of the turbocharger boost. You will need a scan tool capable of reading the turbocharger boost pressure. You may need to monitor the intake manifold pressure, as this will provide the same information. Note the pressure at Key On, Engine Off. After that, start the engine, drive the vehicle to a safe speed, then momentarily accelerate the engine to full throttle, ensuring the engine speed does not exceed 2500-3000 RPM. You should note a change of at least 18 PSI, perhaps more depending on the vehicle manufacturer and the vehicle’s model year. If you cannot achieve a boost pressure of at least 18 psi, a faulty/misadjusted/stuck wastegate, an exhaust restriction, or possibly a faulty turbocharger is indicated.

If this test was successful, or if you were unable to check the turbocharger boost, we will need to test the sensor and its associated circuits. Typically, there are 3 wires at the exhaust pressure sensor.

Disconnect the harness going to the exhaust pressure sensor. With a digital voltmeter (DVOM), test the 5V supply circuit going to the sensor to ensure it is powered (red lead to the 5V supply circuit, black lead to a good ground). If there are 12 volts at the sensor when there should be 5 volts, repair the wiring from the PCM to the sensor for a short to 12 volts, or possibly a faulty PCM.

If that’s okay, with a DVOM, check that the exhaust pressure sensor signal circuit is at 5V (red lead to the sensor signal circuit, black lead to a good ground). If there is no 5 volts at the sensor, or if you see 12 volts at the sensor, repair the wiring from the PCM to the sensor, or again a faulty PCM.

If that checks out, verify that the exhaust pressure sensor ground is good. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the exhaust pressure sensor circuit ground. If the test light does not illuminate, this would indicate a circuit problem. If it lights up, wiggle the wire harness going to the exhaust pressure sensor to see if the test light flickers, indicating an intermittent connection.

If all tests have passed so far and you continue to get a P04A0 code, this would most likely indicate a failing exhaust pressure sensor, although a faulty PCM cannot be ruled out until the sensor has been replaced.