Exhaust Valve Control Circuit (Bank 2)
The engine computer detected a problem with the exhaust valve control system on the right side of the engine (Bank 2). Think of it like a gate that won't open or close properly—the engine can't regulate exhaust flow correctly.
The ECM monitors the exhaust valve actuator solenoid circuit voltage, resistance, and response time on Bank 2. It detects opens, shorts, weak signals, or delayed valve activation by comparing actual response against expected electrical parameters and mechanical timing.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Solenoid Circuit Resistance | 5-15 ohms | <2 ohms or >25 ohms (short or open) |
| Valve Response Time | 50-200 milliseconds | >300 milliseconds (slow or no response) |
Code P0078 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0078 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.