Code
P0078
Generic
P — Powertrain
Exhaust Valve Control Solenoid Circuit Bank 1
Views:
UK: 25
EN: 52
RU: 28
AI status
Completed
Completed
100%
Causes
- Open or short in the exhaust valve control solenoid wiring (bank 1)
- Corroded, loose or damaged connector/pins at the solenoid
- Failed exhaust valve control solenoid (stuck or electrically failed)
- Blown fuse or poor power/ground supply to the circuit
- Low engine oil pressure or contaminated oil preventing valve actuation
- Internal short or failure in the PCM (less common)
Symptoms
- Check Engine Light (MIL) illuminated and code P0078 stored
- Reduced engine performance or limp mode depending on vehicle strategy
- Rough idle or hesitation if valve remains incorrectly positioned
- Unusual valve noise (tapping/rattling) from the exhaust area in some engines
- Poor fuel economy or increased emissions in some cases
What to check
- Retrieve freeze frame and live-data with a capable scan tool; note any related oil pressure or cam timing data
- Inspect wiring harness and connector at the exhaust valve control solenoid for damage, corrosion, pushed-out pins or oil contamination
- Check engine oil level and condition (very low/dirty oil can affect operation)
- Verify fuses and power/ground availability to the solenoid circuit
- Measure solenoid coil resistance with a meter and compare to factory spec
- Backprobe solenoid connector and command the solenoid with a scan tool while observing voltage/pulse and ground continuity
Signal parameters
- Typical coil resistance (approx): 10–40 Ω (varies by manufacturer) — consult factory spec
- Control signal: PWM switching between ~0 V and battery voltage when commanded (duty cycle varies with command)
- Expected commanded frequency: typically tens to low hundreds of Hz (vehicle-specific)
- No continuous solid battery voltage at the control pin when solenoid is un-commanded; no open-circuit (infinite Ω) or direct short to battery
Diagnostic algorithm
- Connect a scan tool; note freeze-frame and any related codes (camshaft/cylinder bank/oil pressure).
- Visually inspect wiring and connector at the bank 1 exhaust valve control solenoid. Repair obvious damage. Check engine oil level and top/reset as needed.
- With ignition OFF disconnect connector and measure solenoid coil resistance; compare to factory spec. Infinite or very high resistance indicates open coil; near 0 Ω indicates short. Do not assume PCM—replace solenoid if out of spec.
- Reconnect and backprobe harness. With key ON and engine off, verify battery power and ground presence at the circuit where expected. Check for blown fuses or relays supplying the circuit.
- With engine running or while commanding the solenoid with the scan tool, observe control signal for PWM voltage and duty response. No pulse or a stuck voltage indicates harness/PCM/relay issue.
- Wiggle test harness while monitoring live data to find intermittent faults. Repair any damaged wiring and retest.
- If wiring and solenoid check good, try swapping a known-good identical solenoid (if available) to confirm component failure. After repair, clear codes and perform a road test to confirm the fault does not return.
- If problem persists after replacing solenoid and repairing wiring, perform PCM circuit checks per factory procedures and consider module testing/replacement as a last step.
Likely causes
- Connector corrosion or bent pins at solenoid harness
- Damaged insulation causing intermittent short to ground or power
- Failed solenoid coil (open or shorted)
- Low oil level/dirty oil restricting valve movement
- Blown inline fuse or poor ground connection
Fault status
Status
MIL illuminated. PCM has detected fault in Exhaust Valve Control Solenoid Circuit — Bank 1 (open/short/implausible signal).
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
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