Technical Description of OBD-II Trouble Code
The exhaust pressure control valve “B” is operating at a high level.
What does this mean?
This generic diagnostic trouble code is typically found in diesel engines, including certain Ford Powerstroke, Dodge Cummins, Mercedes, Nissan, and VW vehicles. It can also apply to trucks with diesel engines and dealer-installed exhaust brakes.
An exhaust pressure control valve is placed in the exhaust stream after the exhaust manifold. It generates heat in the form of back pressure, which can be used for cold start warm-up and to slow down the engine and vehicle during towing. This code specifically relates to the exhaust pressure sensor not matching intake manifold pressure or ambient air pressure during normal driving. It can be caused by a mechanical or electrical circuit fault, depending on the vehicle manufacturer.
Troubleshooting steps may vary depending on the manufacturer, type of exhaust back pressure control, and wire colors to the control solenoid. Consult a vehicle-specific repair manual to identify the “B” valve in your particular case.
Symptoms
Common symptoms of a P04A2 engine code may include:
Potential P04A2 Causes
The typical causes for this code to set are:
Diagnostic and Repair Procedures
A good starting point is to search for any technical service bulletins (TSBs) related to your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogram to address this issue. It is important to check this before proceeding with any repairs. PCM stands for powertrain control module.
Next, locate the “B” exhaust pressure sensor on your vehicle and visually inspect the connectors and wiring. Look for any signs of damage such as chafing, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connectors and inspect the terminals for corrosion or damage. Clean the terminals if necessary using electrical contact cleaner or rubbing alcohol. Apply dielectric silicone compound to ensure proper contact.
If your vehicle is equipped, remove the sensing tube that connects the exhaust backpressure sensor to the exhaust manifold and check for any blockages. If the tube is blocked, it can cause this code to set.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if the code returns. If it does not, the issue was likely with the connections.
If the code does return, you will need to verify proper turbocharger boost operation. Use a scan tool that can read turbocharger boost pressure or intake manifold pressure. Note the pressure at key on, engine off, and then during driving and acceleration. There should be a noticeable change in pressure.
If the turbocharger boost test passed or if you were unable to perform it, you 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 and use a digital volt ohm meter (DVOM) to test the 5V power supply circuit. Ensure that it is receiving the correct voltage. If there is an incorrect voltage, repair the wiring or consider a possible PCM issue.
If the power supply circuit is functioning correctly, test the signal circuit to ensure it is receiving 5V. If there is no voltage or an incorrect voltage, repair the wiring or consider a possible PCM issue.
Finally, check the ground circuit at the exhaust pressure sensor using a test light. If the test light does not light up, there is a problem with the circuit. Wiggle the wiring harness to check for intermittent connections.
If all previous tests have passed and the P04A2 code continues to appear, it is likely that the exhaust pressure sensor has failed. However, a stuck closed exhaust backpressure valve or a failed PCM cannot be ruled out until the sensor is replaced.
