P0078

Exhaust Valve Control Solenoid Circuit Bank 1

Q: 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.

Q: 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.

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.

Real-world scan data

Seen in

127

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P0078 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX