P0478 Code - Exhaust Pressure Control Valve High

What Does P0478 Mean?

The PCM calculates the proper exhaust back pressure based on data from various sensors, according to the manufacturer’s specifications. It then compares this value with the actual exhaust back pressure reading, which is controlled by the exhaust back pressure valve. If the actual voltage value is too high, the PCM will store the P0478 code.

What are the common causes of P0478 ?

In most cases, this code is caused by a clogged back pressure tube and/or exhaust back pressure sensor. However, technicians also report that damaged and burnt electrical wiring and connectors are a possibility. The PCM could also be faulty but this is highly unlikely.

How do you troubleshoot P0478 ?

The valves of each cylinder are kept closed using a pair of arms that replace the conventional engine's roller-type rocker arm. P0478 code one of these arms follows the cam profile while the second arm connects to the valves. During normal engine operation the two arms are joined by a locking pin.

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