Exhaust Pressure Control Valve Circuit High
The P0478 code means the vehicle's onboard diagnostic system has detected: Exhaust Pressure Control Valve Circuit High. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $150 - $600 (parts and labor)
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Common Symptoms
- Check Engine Light on
- Exhaust pressure too low (no back pressure)
- Exhaust brake inoperative
- DPF may not regenerate
Probable Causes (Ranked by Likelihood)
- Open circuit in control valve wiring Very High
- Burned-out valve solenoid High
- Disconnected connector Moderate
- PCM driver open Low
Frequently Asked Questions
What happens without exhaust back pressure control?
Without the control valve, the turbo may not spool efficiently, DPF regeneration may not work, and the exhaust brake will be disabled.
Can the solenoid burn out from heat?
Yes, the valve is in the exhaust system exposed to extreme temperatures. Solenoid coils can fail open from prolonged heat exposure.
Is P0478 common on diesel trucks?
Yes, especially on high-mileage diesel trucks. The exhaust environment is harsh and components degrade over time.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Measure valve solenoid resistance. Infinite ohms confirms open.
-
Check connector is seated.
-
Test wiring continuity.
-
Replace valve if open.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2010-2020 Ram 3500 (6.7L Cummins)
- 2012-2019 Ford F-350 (6.7L Diesel)
- 2008-2018 GMC Sierra 3500 (6.6L Duramax)
- 2011-2020 Chevrolet Silverado 3500 (6.6L Duramax)
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