P257C
Vacuum Reservoir Control Circuit High
The vacuum reservoir control circuit reads stuck high — short to battery voltage or open coil. The driver cannot pull the line low to actuate the valve/motor.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Control wire shorted to battery voltageCommon
- Open coilPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Vacuum Reservoir Control Valve
P257C is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.