Exhaust Valve Control Solenoid Circuit (Bank 1)
The P0078 code means the vehicle's onboard diagnostic system has detected: Exhaust Valve Control Solenoid Circuit (Bank 1). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $80 - $450 (parts and labor)
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Common Symptoms
- Check Engine Light on
- Rough idle and poor engine performance
- Reduced fuel economy
- Engine may stall at low RPM
Probable Causes (Ranked by Likelihood)
- Faulty exhaust VVT solenoid Very High
- Low engine oil level or sludged oil High
- Damaged wiring to exhaust VVT solenoid Moderate
- PCM/ECM driver failure Low
Step-by-Step Diagnostic Procedure
-
Check engine oil level and condition first. Low or dirty oil is the leading cause of VVT solenoid problems.
-
Locate the exhaust VVT solenoid on Bank 1. Measure resistance: typical 6.9-7.9 ohms depending on manufacturer.
-
Inspect wiring and connector for heat damage (exhaust VVT solenoids are close to hot exhaust components).
-
Use a scan tool to command the solenoid and monitor exhaust camshaft position response.
Frequently Asked Questions
What is the exhaust valve control solenoid?
It is the VVT solenoid that controls exhaust valve timing. By adjusting when exhaust valves open and close, it optimizes emissions and performance across the RPM range.
Is the exhaust VVT solenoid different from the intake VVT solenoid?
Yes, they control different camshafts. The exhaust solenoid adjusts exhaust valve timing while the intake solenoid adjusts intake valve timing. Both are part of the VVT system.
Can I drive with P0078?
You can drive short distances, but the engine will not perform optimally. Extended driving may increase exhaust emissions and reduce fuel economy.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0078 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
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