P0078
Exhaust Valve Control Solenoid Circuit Bank 1
Exhaust valve control (VVT)
Generic OBD-II
High
What it means
P0078 means the ECM has detected an electrical fault in the exhaust valve control (variable valve timing) solenoid circuit on bank 1. With the solenoid circuit faulty, exhaust valve timing can't be adjusted as commanded, so the engine may lose some power and run less smoothly. It normally still starts and drives, but should be repaired to restore performance.
High
Can I keep driving? Generally driveable, but exhaust valve timing on bank 1 may not respond correctly — expect some power loss and rougher running until repaired.
Common symptoms
What you'll notice
- Check-engine light on
- Reduced power or hesitation on acceleration
- Rough or unstable idle
- Slightly reduced fuel economy
Common causes
Most likely first
- Failed exhaust valve control (VVT) solenoid on bank 1Likely
- Open or shorted wiring in the solenoid circuitCommon
- Loose or corroded connectorCommon
- Sticking solenoid or restricted oil flow from dirty/low oilLess often
- Failed ECM driver (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data, then inspect the bank 1 exhaust valve solenoid connector and wiring for damage or corrosion.
- Check the control circuit for an open or short against the wiring diagram.
- Measure the solenoid resistance and check oil level/condition, since the solenoid is oil-actuated.
- Replace the solenoid if faulty; consider the ECM only last. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0078?+
Yes for short distances, but exhaust valve timing may be off, hurting power and smoothness, so have it checked soon.
Can I just clear P0078?+
This is a circuit code, so it returns once the ECM re-tests the solenoid until the wiring or part is repaired.
Related codes
Often seen with P0078
Read & clear P0078 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX