What it means
The control module detects an electrical fault in the Bank 1 exhaust valve control solenoid circuit. The code alone does not establish what the controlled exhaust valve does on a particular vehicle.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The exhaust valve control solenoid on bank 1 operates a vehicle-specific exhaust valve-control function. The control module monitors the solenoid circuit and sets P0078 when it detects an electrical fault, but the code alone does not identify the controlled valve's purpose or the exact circuit failure.
Common causes
Most likely first.
- Exhaust valve control solenoid coil failed
- Damaged wiring or connector
- Poor electrical connection
- Solenoid stuck or mechanically binding
Symptoms
- Check-engine light on
- Reduced engine power
- Rough idle or hesitation
- Poor acceleration
How to diagnose it
- Record freeze-frame data and check for related exhaust valve-control codes before clearing anything.
- Use vehicle service information to locate the bank 1 exhaust valve control solenoid, then inspect its connector and wiring for looseness, corrosion, heat damage, or chafing.
- Check the solenoid circuit for opens and shorts with the wiring diagram and manufacturer's test procedure.
- Measure the bank 1 exhaust solenoid coil and compare it with the manufacturer's specification.
- If the circuit and coil pass, check for a sticking solenoid or binding controlled mechanism according to the vehicle's service procedure.
Common fixes
- Reconnect and secure the bank 1 exhaust valve control solenoid connector.
- Repair damaged wiring or poor connector terminals.
- Replace the bank 1 exhaust valve control solenoid if its coil fails testing.
- Correct a sticking solenoid or binding exhaust valve-control mechanism.
Can I keep driving?
If the engine runs smoothly, a short drive may be possible, but reduced power or hesitation can make traffic maneuvers unsafe. Avoid hard acceleration and stop if the engine runs severely rough.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.