What it means
The vacuum pump control circuit B is detected as open. The code does not establish that the pump is electric or that brake-servo or HVAC performance will be affected.
At a glance
- Usually lights the check-engine light
How it works
Circuit B is the identified control circuit for the vacuum pump system; this code does not establish the pump design or which vehicle function it serves. The module detects an open in circuit B, such as a broken control wire or an open winding or brush path in the pump where an electric pump is fitted.
Common causes
Most likely first.
- Open pump motor winding or worn brushes
- Broken control wire between ECU and pump
Symptoms
- Brake pedal may feel harder than usual
- HVAC airflow or operation may be reduced
How to diagnose it
- Check freeze-frame data and warning indicators, then note any change in brake pedal effort or HVAC operation without assuming either symptom is caused by this code.
- Inspect the circuit B connector and harness at the pump and along the accessible route for unplugged connectors, broken wires, or corrosion.
- With power isolated as specified by the manufacturer, check continuity through circuit B and its connections to locate an open.
- If the vehicle has an electric pump, test its winding and brush path for an open according to the manufacturer's procedure.
- If the pump and wiring pass, verify the circuit B control output and related feedback at the module.
Common fixes
- Reconnect a loose circuit B connector and clean corroded terminals.
- Repair a broken circuit B control wire.
- Replace an electric pump with an open winding or worn brushes if confirmed by testing.
- Repair the module control connection if testing isolates the open there.
Can I keep driving?
If the brake pedal feels harder than usual, leave extra stopping distance and avoid driving until brake assist is checked; reduced vacuum may affect braking. If pedal effort is normal, arrange diagnosis soon and watch for changes in braking or HVAC operation.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.