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P0477 is a diagnostic trouble code (DTC) for "Exhaust Pressure Control Valve Low". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
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.
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.
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:
In some very rare cases, a faulty PCM may be to blame for the P0477 code being stored.
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.
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.
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.
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.
Repairing the issue that caused the PCM to store the P0477 code can take many forms. Repairs may include:
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