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
Step-by-Step Diagnostic Procedure
-
Measure valve solenoid resistance. Infinite ohms confirms open.
-
Check connector is seated.
-
Test wiring continuity.
-
Replace valve if open.
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.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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