What it means
Brake Booster Motor A Position Sensor Supply Circuit Low: the signal voltage is below the expected range. The electric brake booster generates the braking assist; a motor or sensor fault can reduce or disable power-assisted braking. Safety-relevant.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
The position sensor for brake booster motor A needs a supply circuit so it can report motor position to the brake control module. This code sets when that supply voltage is below the expected range. A short to ground, corroded connector pins, or chafed supply wiring can pull the circuit low and affect electric brake assistance.
Common causes
Most likely first.
- Supply wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Read brake-module freeze-frame and live data to confirm the motor A position sensor supply is low and check for related booster faults.
- Inspect the motor A sensor connector and supply harness for corrosion, chafing, or contact with ground.
- Using the wiring diagram, test whether the sensor supply circuit is shorted to ground.
- Check connector terminal condition and circuit continuity between the sensor and brake control module.
- If wiring and connections pass, test the sensor and module supply output according to the manufacturer's specification.
Common fixes
- Repair chafed motor A sensor supply wiring.
- Clean or replace corroded connector terminals.
- Repair a short to ground in the supply circuit.
- Replace the position sensor if it is pulling the supply low and the circuit is sound.
- Repair the module supply connection only if testing confirms the fault there.
Can I keep driving?
Power-assisted braking may be reduced or lost, and the vehicle may enter a limited operating mode. Stop safely and arrange recovery if pedal effort rises or braking performance changes.
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.