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P0478 Severity
Once the vehicle's onboard system no longer detects the issue, most codes will disappear on their own. If your vehicle still has this code, however, it should be properly diagnosed to avoid a more serious problem.
For a proper diagnosis, RepairPal Certified shops have the equipment, tools, and expertise.
Moderate severity codes might not threaten the vehicle's safety or functionality immediately, but you should still get it diagnosed within a reasonable time frame to keep your car running well.
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.
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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.