What Does P0478 Code Mean?

    OBD-II Code P0478 is defined as a Exhaust Pressure Control Valve "A" High

    The Exhaust Pressure Control Valve controls exhaust back pressure during engine warmup. If the engine control module (PCM) determines there is an incorrect signal from the Exhaust Pressure Control Valve, the PCM will set code P0478.

    Common Problems That Trigger the P0478 Code

    • Exhaust pressure control valve failure
    • Powertrain Control Module (PCM) failure
    • Wiring issue

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