What does code P257B mean?

Q: What does code P257B mean?

Vacuum Reservoir Control Circuit Low. P257B indicates that the powertrain control module (PCM) has detected an abnormally low voltage on the electrical circuit that controls the vacuum reservoir, which stores engine vacuum for systems like the brake booster or HVAC actuators. The PCM monitors the control circuit and sets this code when the signal voltage falls below the expected threshold, indicating a short to ground, an open circuit, or a faulty component.

DTC codes / P25xx · Vehicle speed, idle control and auxiliary inputs / P257B

P257BVacuum Reservoir Control Circuit Low

P257B indicates that the powertrain control module (PCM) has detected an abnormally low voltage on the electrical circuit that controls the vacuum reservoir, which stores engine vacuum for systems like the brake booster or HVAC actuators. The PCM monitors the control circuit and sets this code when the signal voltage falls below the expected threshold, indicating a short to ground, an open circuit, or a faulty component.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.