Powertrain, generic (extended)

P257C Vacuum Reservoir Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Control wire shorted to a battery-voltage line
Internal fault in the reservoir control valve
Faulty output stage in the engine control module

Symptoms

  • Engine warning lamp on
  • Weaker boost or EGR response in some cases

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–300
Time0.3–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

vacuum reservoir control valve

Related codes

P257AP257BP2528

References: law.cornell.edu, static.nhtsa.gov.