What are the common causes of P257B?

A short to ground on the vacuum reservoir control circuit. An open in the vacuum reservoir control wiring. A failed vacuum reservoir control solenoid. Low battery voltage weakening the control signal.

Read the vacuum reservoir control circuit on a scan tool. Test the vacuum reservoir control circuit for a short to ground. Check the vacuum reservoir control wiring for an open. Check battery voltage and connections. Replace the vacuum reservoir control solenoid if the circuit tests good. Clear the code and retest.

P257B

Vacuum Reservoir Control Circuit Low

System: Speed and idle control (P code)
Lamp: Check Engine Light
Category: Powertrain - Computer and Auxiliary Controls

What it means

P257B means Vacuum Reservoir Control Circuit Low.

Check these first

A short to ground on the vacuum reservoir control circuit
An open in the vacuum reservoir control wiring
A failed vacuum reservoir control solenoid
Low battery voltage weakening the control signal

What to do next

Read the vacuum reservoir control circuit on a scan tool
Test the vacuum reservoir control circuit for a short to ground
Check the vacuum reservoir control wiring for an open
Check battery voltage and connections
Replace the vacuum reservoir control solenoid if the circuit tests good
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.