Variable Cam Timing Overadvanced (Bank #2)
The camshaft on Bank 2 is advancing (rotating) too far ahead of its target timing, like an engine trying to breathe in too early and throwing off combustion. This timing mismatch prevents the engine from running optimally and triggers the fault code.
The ECU monitors camshaft position using the CMP sensor on Bank 2 and compares actual timing to the target timing controlled by the VVT solenoid. When the camshaft advances beyond the calibrated threshold, the ECU detects the overadvance condition and sets the code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Cam Timing Advance (Bank 2) | Within ±5 degrees of target | Exceeds +8 degrees from target |
| VVT Solenoid Response | Solenoid engages/disengages within 200ms | Solenoid stuck or delayed >500ms |
Code P1391 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, P1391 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.