P257CVacuum Reservoir Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P257C sets when the control line of the vacuum reservoir valve reads too high, typically from a short to battery positive or a fault in the driver stage, so the valve can no longer be switched as commanded. The reservoir serves pneumatic actuators on diesel engines; GM's bulletin PI1260 on the 2014 Cruze diesel names leaks anywhere in the vacuum system that feeds the turbo vane and EGR actuators as a cause of P003A, P2598 and P2599, which shows how a fault here spreads to boost control. No manufacturer documents P257C itself. CARB 13 CCR 1968.2 requires circuit checks on such output components. P257A covers an open line and P257B a short to ground, while sensor faults on the reservoir itself are reported as P2525-P2529. The driver will mostly notice the warning lamp and, at worst, weaker boost.
- What you may notice
- Engine warning lamp on
- Weaker boost or EGR response in some cases
- Likely causes
- LikelyControl wire shorted to a battery-voltage line
- PossibleInternal fault in the reservoir control valve
- RareFaulty output stage in the engine control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.