P257A is an output fault on the control line of the vacuum reservoir, usually a solenoid or switching valve the engine computer uses to connect, isolate or vent a vacuum storage tank. Such tanks occur mainly on diesels whose EGR valves, turbocharger vanes or flaps are worked by vacuum; GM bulletin PI1260 for the 2014 Cruze 2.0 L diesel, for example, shows the pump filling a tank built into the EGR cooler, which in turn feeds the turbo and EGR control solenoids. The driver stage logs it on an open circuit or on a fault it cannot assign to low or high. No manufacturer documents P257A publicly; CARB 13 CCR 1968.2 treats such outputs as comprehensive components to be checked for circuit faults. P257B and P257C cover shorts to ground and to voltage.
Medium severity. Can I keep driving?If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
Symptoms
- Engine warning lamp on
- Vacuum-driven actuators such as EGR or turbo vanes respond poorly
Most likely causes
- Loose or corroded connector at the reservoir control valve
- Broken wire in the control or supply line
- Open solenoid coil in the control valve
- Faulty output stage in the engine control module
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P257A means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 5: Speed and idle
- 7A: Specific fault in that system
Frequently asked questions
Can I keep driving with code P257A?
If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
What causes code P257A?
The most common causes are: loose or corroded connector at the reservoir control valve; broken wire in the control or supply line; open solenoid coil in the control valve.
Related codes
- P257BVacuum Reservoir Control Circuit Low
- P257CVacuum Reservoir Control Circuit High
- P2525Vacuum Reservoir Pressure Sensor Circuit
- P2526Vacuum Reservoir Pressure Sensor Circuit Range/Performance
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.