Technical Description of OBD-II Trouble Code
The performance of the Exhaust Pressure Control Valve “A” is outside the expected range.
What does that mean?
This diagnostic trouble code is commonly found in diesel engines, specifically in certain Ford, Dodge, Mercedes, Nissan, and VW vehicles. It can also occur in trucks with diesel engines and dealer-installed exhaust brakes.
An exhaust pressure control valve is placed in the exhaust stream after the exhaust manifold. Its purpose is to generate heat and back pressure in the exhaust. This heat and pressure can assist in cold start warm-up and slow down the engine and vehicle by opposing cylinder pressure coming from the engine cylinders out of the exhaust. This is particularly useful during towing operations.
This code specifically relates to the exhaust pressure sensor not matching intake manifold pressure, ambient air pressure, or preprogrammed information during normal driving. The cause can be either 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.
Symptoms
Common symptoms of a P0476 engine code may include:
Potential Causes
The typical causes for this code to set are:
Diagnostic and Repair Procedures
A good starting point is to search for a technical service bulletin (TSB) specific to your vehicle. The vehicle manufacturer may have a PCM flash/reprogram to address this issue, so it’s worth checking before proceeding. PCM stands for powertrain control module.
Next, check for any exhaust leaks. Listen for exhaust noise coming from all exhaust manifolds and pipes, and look for black soot at the location of the leak. If a leak is present, repair the exhaust leak first.
Locate the 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 inside for corrosion, burns, or unusual discoloration. If cleaning of the terminals is necessary, use Electrical Contact cleaner or rubbing alcohol and a light plastic bristle brush. After cleaning, let them air dry and apply dielectric silicone compound to prevent future corrosion.
If your vehicle is equipped, remove the sensing tube that connects the exhaust backpressure sensor to the exhaust manifold and attempt to blow through it. If you are unable to blow through it, this could be a possible cause for the code.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if the code returns. If it does not, then 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 monitor intake manifold pressure. Note the pressure at Key On, but with the Engine Off. Start the engine, drive the vehicle at a safe speed, and momentarily accelerate the engine to wide open throttle without exceeding 2500-3000 RPMs. You should observe a change of at least 18 PSI, possibly more depending on the vehicle manufacturer and year. If you are unable to obtain at least 18 psi boost pressure, it indicates a faulty/misadjusted/stuck wastegate, an exhaust restriction, or possibly a faulty turbocharger.
If the turbocharger boost test passed or you were unable to perform it, the next step is 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 (5V) by connecting the red lead to the 5V power supply circuit and the black lead to a good ground. If there is 12 volts instead of 5 volts, repair the wiring from the PCM to the sensor for a short to 12 volts or consider a possible bad PCM.
If the power supply circuit is functioning correctly, use the DVOM to check the sensor signal circuit. Connect the red lead to the sensor signal circuit and the black lead to a good ground. Ensure that there is a 5V signal to the sensor. If there is no 5 volts or if you see 12 volts, repair the wiring from the PCM to the sensor or consider a possible bad PCM.
Next, check the ground circuit at the Exhaust Pressure sensor. Connect a test light to the positive terminal of a 12V battery and touch the other end of the test light to the ground circuit going to the Exhaust Pressure Sensor. If the test light does not illuminate, it indicates a problem with the ground circuit. If the test light illuminates, wiggle the wiring harness going to the exhaust pressure sensor to check for intermittent connections.
If all tests have passed so far and you continue to get a P0476 code, it most likely indicates a failed Exhaust Pressure sensor. However, a failed PCM cannot be ruled out until the sensor has been replaced.
