What it means
The vacuum pump control circuit B has a range or performance fault. The code does not by itself prove low vacuum output or identify a leak or worn pump.
At a glance
- Usually lights the check-engine light
How it works
Circuit B controls or monitors the vacuum pump system, but this code alone does not prove that vacuum output is low or identify which system uses it. The module detects circuit B operation outside its expected range or response, which can result from a pump, hose, connection, or sensing fault.
Common causes
Most likely first.
- Worn diaphragm or vanes inside the pump
- Cracked vacuum hose or loose connection
- Sensor element aged beyond calibration window
Symptoms
- Brake pedal may feel harder than usual
- HVAC airflow or operation may be reduced
How to diagnose it
- Review freeze-frame data and any circuit B readings to determine what operating condition triggered the range/performance fault.
- Inspect accessible vacuum hoses and connections for cracks, disconnection, or looseness, and inspect the circuit B harness and connector for damage.
- Check the pump's operation and vacuum output using the manufacturer's procedure; do not infer a failed pump solely from this code.
- If output is out of specification, inspect the pump diaphragm or vanes and check for leaks in the connected hose path.
- If pump output and hoses are sound, test the circuit B sensor or feedback element and wiring for readings outside the manufacturer's specification.
Common fixes
- Reconnect a loose vacuum hose or circuit B connector.
- Replace a cracked vacuum hose or repair a leaking connection.
- Replace a worn pump if testing confirms its output is below the manufacturer's specification.
- Replace an aged or faulty circuit B sensing element if its readings are outside specification.
Can I keep driving?
If the brake pedal feels harder than usual, allow more stopping distance and avoid driving until the brake assist system is checked. Otherwise, arrange diagnosis soon and monitor 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.