Error Code P04A1: What It Means & What To Do?

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What happens to your system when the control valve of the exhaust pressure is low? What are the causes of error? OBD-II Code Powertrain Control Module (PCM) describes a failure in the Exhaust Pressure Control Valve "B" Low

As the engine warms up the exhaust back pressure is controlled by the Exhaust Pressure Control Valve. If the engine control module (PCM) detects a weak signal from the Exhaust Pressure Control Valve, then the error code P04A1 is set by the PCM.

When there is a cold ambient temperature, Exhaust Back Pressure Regulator controls exhaust back pressure so that you can increase the cab heat whenever needed and decrease the time that is needed to defrost the windshield. The measured exhaust back pressure, (ambient) intake of the air temperature, engine oil temperature and engine load are used by the Engine Control Module (ECM) so that you can determine the required exhaust back pressure. Switch the output signal circuit to 12 volts which is inside the ECM and by this way you can control the valve position.

Depending on the exhaust back pressure, you can modulate the on/Off time from 0 to 99%. As the engine starts up each time, the exhaust back pressure valve commands it to on and off which is exercised by the ECM. During the start-up, if the temperature of the intake air that is sensed by the Intake Air Temperature (IAT) sensor is < 37°F (5°C) and if the oil temperature that is sensed by the Engine Oil Temperature (EOT) sensor is between 32°-140°F (0-60°C) then it will continue to keep the back-pressure valve half closed. When the oil temperature rises in the engine operation, you can see the ECM controlling the valve in reaction to the rising of the oil temperature.

What causes this problem with the Exhaust Pressure Control Valve "B" Low?

• A direct connection to Power in the power supply circuit that exist between the exhaust pressure control solenoid and the PCM (powertrain control module)
• An opening in the power supply circuit that exist between the exhaust pressure control solenoid and the PCM
• A direct connection to ground in the power supply circuit which goes to the exhaust pressure control solenoid
• Fault in the Exhaust Pressure Control Relay
• Fault in the Exhaust Pressure Control Solenoid faulty
• Possible chances of failure in the PCM

1. Powertrain Control Module - Experiencing trouble with your Powertrain control model? Looking for a place to find the right replacement part? Parts Avatar has everything you’re looking for.
2. Exhaust Pressure Control Valve - If you experience any leak in the Exhaust Pressure Control Valve then rectify the leak area.
3. Exhaust Gas Pressure Sensor - Rectifying the leak in Exhaust Gas Pressure Sensor can help you to get rid of the error code P04A1.
4. Engine Control Module - You will find an error code, if the engine control module detects an incorrect signal from the exhaust pressure control valve.
5. Exhaust Pressure Control Relay - Experiencing a fault in your Exhaust Pressure Control Relay? Then you have to either repair or replace this part.
6. Exhaust Pressure Control Solenoid - Do you have to replace your Exhaust Pressure Control Solenoid? Then Parts Avatar has the right replacement part for every make.

Willing to know some common symptoms of OBD Code P04A1? Your wish is our demand. Have a look at them below:

Common Symptoms

• Illumination of the Malfunction Indicator Lamp (MIL)
• Power Deficiency
• Shortage of engine braking
• The cold engine takes longer time to warm up than normal.

We have listed out some ways which would help you to correct the occurrence of OBD Code P04A1. They are mentioned here as follows:

• Replacing the powertrain control module.
• Repairing the Engine Control Module
• Rectifying the leak in the Exhaust Pressure Control Valve / Pressure Sensor / Control Relay / Control Solenoid

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• If you want to easily diagnose this P04A1 fault code, then all you have to do is to follow the steps which are mentioned below:
• Start searching for a technical service bulletin (TSB) for your particular vehicle. Resolve the issue with the help of PCM flash/ reprogram which the vehicle manufacturer has.
• Check for leaky exhaust. See if there is any black soot where leakage happens and if you detect one, rectify immediately. Listen carefully if there are exhaust noises from the exhaust pipes and manifolds.
• Locate the “B” Exhaust pressure Sensor and inspect the wires and connectors of your vehicle. If there are any burnt spots or molten plastics pull them apart and check for the terminals that is present inside the connectors. Check if they are corroded, burnt or green in colour rather than the normal colour and clean its parts with the help of electrical contact cleaner else, clean them with light plastic brush and 91% rubbing alcohol. Let them dry and apply some dielectric compound around the terminals which come in contact.
• It is good to remove the sensing tube which connects the back-pressure sensor to the exhaust manifold, if your vehicle is well equipped. This can also be one of the reasons for the error in the code.
• Check if the code returns when you clean the diagnostic trouble codes with the help of a scan tool. If the code does not return, then the problem must be with the connections.
• If your code does not return, then you have to turbocharge your boost operation with the help of a scan tool. Keep the engine off, and note the pressure with key on. Now start the engine and drive at a safe speed. Accelerate the engine so that it wide opens the throttle, and see that it does not exceed 2500- 3000 RPMs. There will be a change of 18 PSI or more depending on the manufacture and the year it was made. If you do not get a boost pressure of 18 PSI, then there will be a fault in the turbocharger.
• If you don’t pass the test with the turbocharger boost, then you have to check the sensor and its related circuits. You will have 3 wires of the Exhaust Pressure Sensor.
• Disconnect the wire to the Exhaust Pressure Sensor and now with the help of Digital Volt Ohm Meter (DVOM), you have to test the 5V power supply circuit which goes to the sensor to ensure it is powered up (Red colour to the 5V power supply circuit, black colour to a good ground). Instead of 5 volts to the sensor if there is 12 volts, you have to repair the wire from the PCM to the sensor or it can also be due to a fault in the PCM.
• Check if the exhaust pressure sensor is connected to good ground. Connect a test light to the positive terminal and connect the other end to the ground which reaches the exhaust pressure sensor circuit. You will find a problem with the circuit if the test light does not light up.
• If the test light does not light up, this would indicate the problem circuit. If there is lighting, shake the wire which is connected to the exhaust pressure sensor and see if flickering occurs. It will indicate a broken connection.
• If the P04A1 code still persist, then it is more likely because of a faulty Exhaust Pressure Sensor and even a failed PCM can be one of the reasons until and unless the sensor is replaced.

Common Mistakes When Diagnosing the P04A1 Code

• On diagnosing the P04A1 code, you will see this common mistake
• Failure of the Exhaust pressure control valve
• Faulty Powertrain Control Module (PCM)
• Problem with wiring

P049F - Exhaust Pressure Control Valve "B"

P04A0 - Exhaust Pressure Control Valve "B" Range/Performance

P04A2 - Exhaust Pressure Control Valve "B" High

P04A3 - Exhaust Pressure Control Valve " B" Intermittent

P04A4 - Exhaust Pressure Control Valve "B" Stuck Open

P04A5 - Exhaust Pressure Control Valve "B" Stuck Closed