P257A
Vacuum Reservoir Control Circuit/Open
Vacuum control
Generic OBD-II
Medium
What it means
P257A means the ECU has detected an open circuit in the vacuum-reservoir control. This system stores and manages engine or pump vacuum used for things like brake assist and vacuum-driven actuators, so the fault is electrical — an open wire, bad connector, or failed solenoid/pump. It's worth confirming brake-booster vacuum isn't affected.
Medium
Can I keep driving? Usually drivable, but vacuum runs brake boost and other actuators on many vehicles — if assist is affected the brake pedal can feel hard, so test the brakes carefully.
Common symptoms
What you'll notice
- Check-engine light on
- Firmer / harder brake pedal on vehicles that use the reservoir for boost
- Vacuum-operated functions (actuators, flaps) not working correctly
- Often no obvious change on vehicles where vacuum use is minor
Common causes
Most likely first
- Open circuit in the vacuum-reservoir control wiringLikely
- Faulty vacuum solenoid or electric vacuum pump the ECU controlsCommon
- Corroded or disconnected connector at the solenoid/pumpCommon
- Faulty ECM control outputLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame and check whether the ECU can command the vacuum solenoid/pump on.
- Inspect the control wiring and connector for an open circuit or corrosion.
- Measure the solenoid/pump resistance and its supply and ground.
- Confirm vacuum is actually stored and delivered where the reservoir feeds (e.g. brake booster).
- Repair the open circuit or replace the failed solenoid/pump, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P257A?+
Test the brakes first. On vehicles that use the vacuum reservoir for brake boost, a loss of vacuum makes the pedal hard and braking effort higher — get it repaired promptly if so.
Can I just clear P257A?+
It returns while the control circuit is open or the solenoid/pump is faulty. Clearing it doesn't restore the vacuum control.
Related codes
Often seen with P257A
Read & clear P257A yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX