OBD-II code · Powertrain (generic, extended)
P257B Vacuum Reservoir Control Circuit Low
The vacuum reservoir control circuit reads stuck low — short to ground or low-side driver stuck on. The actuator may be energised continuously when it should be off.
Is it safe to drive with P257B?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyControl wire shorted to ground
- Less likelyConnector pins corroded - high contact resistance
- Less likelyHarness chafing through insulation
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–2 h
- Emissions test
- Usually unaffected
- Parts involved
- Vacuum Reservoir Control Valve
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.