P04A2 OBD Error Code: Problem & Solutions

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A high pressure in the Exhaust pressure Control valve gives rise to the OBD code P04A2, did you know this? Also, as you keep reading you will get to know its symptoms and how they can be rectified. A failure in the OBD - II code Powertrain Control Module defines that Exhaust Pressure Control Valve "B" is High.

As the engine warms up, the exhaust back pressure is controlled by the Exhaust Pressure Control Valve. The PCM will set code P04A2, if the engine control module (PCM) detects an incorrect signal from the Exhaust Pressure Control Valve.

The variable position valve - Exhaust Back Pressure Regulator controls the exhaust back pressure when there are cold ambient temperatures so that you can increase the cab heat and decrease the amount of time when you have to defrost the windshield. The Engine Control Module (ECM) uses the exhaust back pressure, (ambient) intake air temperature, oil temperature of the engine and load of the engine to decide the preferred exhaust back pressure.

The position of the valve is controlled by turning the output signal circuit to 12 volts present inside the ECM. Modulate the on/Off time from 0 to 99 % depending on the exhaust back pressure that you prefer. During the initial start-up of the engine, the ECM trains the exhaust back pressure valve by ordering it to cycle on and off for one time. If the Intake Air Temperature (IAT) sensor, senses the intake air as < 37°F (5°C) during the start-up of the engine and the temperature of the oil sensed by the Engine Oil Temperature (EOT) sensor falls between 32°-140°F (0-60°C) the back-pressure valve will continue to remain partially closed. As you operate the engine and the oil temperature, the ECM will take hold of the valve in response to the rising oil temperature.

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

• Immovable Exhaust Back Pressure Valve
• Limited exhaust
• An Opening in the ground circuit to the exhaust pressure sensor
• An opening in the signal circuit between the PCM and the exhaust pressure sensor
• Shorted voltage in the signal circuit that leads to the exhaust pressure sensor
• Fault in the Exhaust Pressure Sensor – internal voltage short
• The plugged Exhaust Pressure Sensor sensing the over boost of the turbocharger
• Possible chances of fault in the PCM

1. Powertrain Control Module - Replacing your Powertrain Control Module can help you to get rid of this OBD error code P04A2.
2. Exhaust Pressure Control Valve - A leak or any black soot near the leaking area can give rise to this error. It would be fair enough to replace the Exhaust Pressure Control Valve.
3. Exhaust Pressure Sensor - A fault or immovable Exhaust Pressure Sensor has to be get ridden off immediately to avoid this error.
4. Engine Control Module - Replace or repair your Engine Control Module so that it functions effectively.

Our main motive is to achieve customer satisfaction and that’s why we will help you to diagnose P04A2 code by mentioning some major symptoms below:

Common Symptoms

• Illumination of Malfunction Indicator Lamp (MIL)
• Insufficient power
• Insufficient engine brakes
• Lengthier than usual cold engine warm up time

Have a look at some ways with which you can correct the P04A2 code:

• Replacing powertrain control module
• Rectifying the leak in the exhaust pressure control valve/ exhaust pressure sensor
• Replacement of Engine Control module

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Here are some steps which you should follow in order to diagnose this P04A2 fault code:

• Search for the Technical Service Bulletin (TSB) for your vehicle. You can get the PCM flash/ reprogram from your vehicle manufacturer to solve this issue so that you won’t go a long way down through the wrong path.
• Check for leakage in the exhaust. Is there any exhaust noise coming from manifold, pipes, black soot in the leakage area? If your answer is yes, then repair it immediately.
• Now examine the connectors and pipes once you find the “B” Exhaust Pressure Sensor on your vehicle. Do you find any molten plastic, chafing, burn spots? If so, pull the wires apart and check their terminals. Are they corroded, burnt, or green in colour? If you find any of these defects clean them with the help of electric contact cleaner. Also, you can use 91% rubbing alcohol and a light plastic brush as an alternate to clean them. Allow them to dry and apply some dielectric silicone compound in the terminals so they become intact. (Element used for spark plugs and light bulbs)
• Also, if your vehicle is well fit, then remove the sensing tube which links the exhaust backpressure sensor to the exhaust manifold. If you are unable to blow through, then it can also be a reason for this code.
• Check for the returning of the codes by clearing the diagnostic trouble from the memory with the help of a scan tool. If the codes do not return, then the problem was mainly because of the connection.
• Verify the boost operation of your turbocharger, if the code returns. And use a scan tool to read the boost pressure of the turbocharger. The intake manifold pressure will give same information as turbocharger. Note the pressure of the engine with engine off and Key on. Start your vehicle and drive at a safe speed and accelerate it to a wide-open throttle. Make sure the RPM does not exceed 2500-3000. Depending on your manufacturer and the engine make, you will see a change of at least 18 PSI, or more. If you are not able to obtain 18 psi boost pressure, then a fault or immovable wastegate, restriction for the exhaust or a fault in the turbocharger will be indicated.
• If you are unable to check the boost of turbocharger or pass this test, you have to check the associated sensor as well as the circuits. You will find 3 wires at the Exhaust Pressure sensor.
• Disconnect the wire to the Exhaust Pressure Sensor. With a Test the 5V power supply circuit that goes to the sensor with the help of Digital Volt Ohm Meter (DVOM), to make sure it gains power. You have to repair the wire from PCM to sensor, if there is 12 volts instead of 5 volts or it can also be due to a fault in the PCM.
• If the above step if fine, check for 5V on the Exhaust Pressure Sensor signal circuit (connect Red to the sensor signal circuit, and black to a good ground). You have to repair the wire from PCM to sensor, if there is 12 volts instead of 5 volts or it can also be due to a fault in the PCM.
• Check for a good ground at the Exhaust Pressure sensor. Take a test light and connect it to 12V battery positive that is red terminal and touch the other end to the ground circuit which leads to the Exhaust Pressure Sensor circuit ground. You will face an error, if the test light does not light up.
• Check if the light flickers when you shake the wire that connects to the exhaust pressure sensor. It will indicate a discontinuous connection.
• If you still get P04A2 code despite of passing all the test, then the problem is with the Exhaust Pressure sensor, although you cannot skip a faulty PCM until it is replaced.

Common Mistakes When Diagnosing the P04A2 Code

You will face errors in the following parts when diagnosing the P04A2 code

• Faulty Exhaust pressure control
• Faulty Powertrain Control Module
• Issues with wiring