What it means
The control circuit driving the electric vacuum pump (used to maintain brake-booster vacuum on direct-injection or hybrid powertrains where the engine is not always running) is open. The ECM cannot run the pump on demand — booster vacuum drops, pedal feel hardens, brake assist may be reduced.
At a glance
- Usually lights the check-engine light
How it works
An electric vacuum pump supplies vacuum for the brake booster on vehicles where engine vacuum may be unavailable or insufficient. The engine control module monitors the pump's control circuit and sets this code when circuit A is open and the pump cannot be switched on as requested. Without enough booster vacuum, brake assist can decrease and the pedal can become harder to press.
Common causes
Most likely first.
- Open control wire to the pump
- Failed driver in the control module
Symptoms
- Brake warning light may come on
- Brake pedal may feel harder than usual
- Reduced brake assist may occur
How to diagnose it
- Check for brake-system warnings and note whether the pedal is unusually hard; if braking feels unsafe, do not continue driving.
- Read freeze-frame and pump command data to confirm when circuit A was requested and whether the pump responded.
- Inspect the vacuum pump connector and circuit A wiring for disconnected plugs, broken wires, corrosion, or damage.
- Use the vehicle's wiring diagram to check circuit continuity and the pump's power and ground path as specified by the manufacturer.
- If the circuit wiring is intact, test the control-module output and pump operation using the manufacturer's procedure.
Common fixes
- Reconnect a loose vacuum-pump plug.
- Repair an open or damaged wire in control circuit A.
- Repair a poor power, ground, or connector connection at the pump.
- Repair a confirmed failed control-module driver or replace the pump if it is also found faulty.
Can I keep driving?
Because this fault can reduce brake assist, avoid driving if the pedal is hard or braking takes more effort; arrange safe recovery or prompt repair. Do not assume the brakes will retain normal assist during repeated stops.
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.