What it means
The vacuum pump control circuit reads stuck high — short to battery voltage or open coil/return. The driver cannot pull the line low to start the pump.
At a glance
- Usually lights the check-engine light
How it works
The engine or brake control module switches a vacuum pump on when engine vacuum cannot provide enough brake assist. It monitors control circuit A for the pump command and detects a high signal when the circuit cannot be pulled low, such as from a wire shorted to battery voltage or an open pump winding or return.
Common causes
Most likely first.
- Control wire shorted to battery voltage
- Open pump motor winding
Symptoms
- Brake warning light may come on
- Brake pedal may feel harder than usual
- Brake assist may be reduced or unavailable
How to diagnose it
- Check for related brake and vacuum-pump codes, then review freeze-frame data to see when the control circuit fault occurred.
- With the vehicle safely parked, inspect the vacuum pump, its connector, and control-circuit-A wiring for loose connections, damage, or contact with power wires.
- Use scan-tool data or output controls, if available, to see whether the module commands the pump and whether the circuit responds.
- With power isolated as specified by the manufacturer, check circuit A for continuity and shorts to battery voltage, and check the pump winding and return path against the manufacturer's specification.
- If the wiring and pump test correctly, check the control module output and circuit operation using the manufacturer's diagnostic procedure.
Common fixes
- Repair chafed control-circuit-A wiring shorted to battery voltage.
- Clean and secure the vacuum-pump connector and repair damaged terminals.
- Repair an open pump return or ground connection.
- Replace the vacuum pump if its winding is open.
Can I keep driving?
Treat a hard pedal, brake warning, or reduced assist as a safety issue: avoid driving and arrange repair or towing. If assist is still normal, drive only as needed and allow extra stopping distance, since brake assist can be reduced or lost.
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.