What causes a P0478 code?

P0478 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a P0478 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0478 active.

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

OBD-II

P0478

Exhaust Pressure Control Valve High Input

What it means

The Engine Control Module (ECM) has detected voltage from the exhaust pressure control valve sensor that exceeds the calibrated limit, indicating a potential blockage or circuit failure.