Skip the auto shop - Our mechanics make house calls

P0477 OBD-II Trouble Code: Exhaust Pressure Control Valve Low

check engine light

P0477 code definition

The P0477 code means that the PCM has detected an abnormally low voltage reading from the exhaust back pressure control valve circuit. This code may be stored along with other codes that relate to the exhaust back pressure control system, such as the P0478 and P0479 codes.

What the P0477 code means

The exhaust back pressure valve controls the exhaust back pressure. The circuit connected to the valve obtains data regarding the pressure in volts, and sends this data to the PCM. If the PCM registers that the actual voltage of the exhaust back pressure is lower than the manufacturer’s specifications, it will store the P0477 code.

What causes the P0477 code?

In many cases, this code is caused by a clogged back pressure tube, or a clogged exhaust back pressure sensor. There may also be damaged or burnt electrical wiring that has caused this code to be stored.

Other causes may include:

  • Faulty exhaust back pressure valve.
  • Opened or shorted exhaust back pressure valve harness.
  • Poor electrical connection in the exhaust back pressure valve circuit.
  • Faults in the exhaust back pressure (EBP), the engine oil temperature (EOT), or the intake air temperature (IAT) sensors.

In some very rare cases, a faulty PCM may be to blame for the P0477 code being stored.

What are the symptoms of the P0477 code?

Before the P0477 code is detected, there may be some detectable symptoms. These include reduced engine performance, insufficient turbocharger pressure, and the illumination of the Check Engine Light.

How does a mechanic diagnose the P0477 code?

In order to diagnose the P0477 code, an OBD-II scanner is necessary. After obtaining all stored codes from the PCM, the mechanic can begin by visually inspecting all the electrical wiring, connectors, and other components related to the exhaust back pressure system. If these are repaired, replaced, or already in good condition, then the mechanic may move on to other repair options.

Common mistakes when diagnosing the P0477 code

As with other codes related to the exhaust back pressure system, it is common to misdiagnose this code as having something to do with the exhaust gas recirculation system. These two systems are located near each other, but are diagnosed and repaired in totally different ways.

It is also common to forget to clear the PCM memory of all codes and perform a retest of the system after each potential repair. This step is important, because it helps narrow down the possible root cause until the malfunction is found and repaired.

How serious is the P0477 code?

The P0477 code is a moderately serious code. Left un-repaired, the issue that caused the P0477 code may have an effect on the performance of the vehicle, causing it to perform at a less than optimal level. Additionally, it is likely that the vehicle would not pass an emissions test while the issue that caused the code remains un-repaired.

What repairs can fix the P0477 code?

Repairing the issue that caused the PCM to store the P0477 code can take many forms. Repairs may include:

  • Unclogging or repairing the back pressure tube.
  • Cleaning, repairing, or replacing the exhaust back pressure sensor.
  • Repairing or replacing a faulty exhaust back pressure valve.
  • Repairing or replacing an opened or shorted exhaust back pressure valve harness.
  • Repairing a poor electrical connection in the exhaust back pressure valve circuit.
  • Replacing faulty exhaust back pressure valve solenoids.
  • Repairing or replacing any faulty electrical components, such as wiring or connectors.
  • Replacing a faulty PCM in certain rare cases.
  • Diagnosing and repairing any issues related to other codes stored in the PCM regarding the back exhaust pressure system.
  • Repairing or replacing faulty EBP, EOT, or IAT sensors.

Need help with a P0477 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How Long Does a Vacuum Brake Booster Check Valve Last?
The braking system on your car requires a lot of pressure. The vacuum booster is one of the main sources of this pressure. This booster will take the pressure that...


Related questions

Q: Car will crank, doesnt stay running

Hello and thanks for your question. Ground wires will not have a voltage on them. Preform a resistance check on all of the pins to the harness plug. There should be resistance for the computer, high resistance for the power,...

Q: Cant get my car out of limp mode or "fail safe mode"

The reason "limp mode" has become "unbypassable" is due to the existing codes. The ECT failure, if it exists, may alone account for that because an engine coolant temperature sensor is essentially a master sensor - the value of which...

Q: What are these codes that appeared on my car?

These codes are related to the engine sensors for mass air flow, idle air control, and the throttle position sensor. It is quite likely, given your mileage, that their sensors have become dirty/clogged, or the sensors have failed. You don't...