What it means
The driveline control module monitors position sensor B on rear differential actuator A and sets this code when its signal indicates a sensor or circuit fault.
How it works
Position sensor B on rear differential actuator A provides a second position signal to the driveline control module. C009A sets when sensor B’s signal indicates a fault or falls outside the expected limits, potentially leaving the module unable to verify actuator A’s position.
Common causes
Most likely first.
- Faulty actuator position sensor
- Damaged or corroded sensor connector
- Open or shorted sensor wiring
- Rear differential actuator fault
Symptoms
- AWD or 4WD warning
- AWD may be unavailable or limited
- Rear differential may not engage or disengage correctly
How to diagnose it
- Check freeze-frame and live data specifically for actuator A position sensor B, and observe whether its reading responds to commanded actuator movement.
- Inspect sensor B’s connector and the actuator A harness for corrosion, loose terminals, chafing, or damage from nearby driveline components.
- Compare sensor B’s reading with the actuator A command and available companion position data to identify an absent, erratic, or implausible signal.
- Test sensor B’s power, ground, and signal circuit for opens, shorts, and high-resistance connections using the wiring information for the vehicle.
- If the circuit is sound, test sensor B and check whether actuator A moves freely according to the manufacturer’s diagnostic procedure.
- After repairs, clear the code and verify sensor B data during the same type of actuator operation that triggered the fault.
Common fixes
- Clean and secure the sensor B connector on rear differential actuator A.
- Repair a damaged, open, or shorted section of sensor B wiring.
- Replace position sensor B if the signal remains faulty with correct circuit supply and ground.
- Repair or replace actuator A if its movement prevents sensor B from reporting position correctly.
- Perform the manufacturer’s actuator calibration if the diagnostic procedure calls for it.
Can I keep driving?
AWD may be limited, and the rear differential may not engage or release as intended. Avoid demanding 4WD/AWD use until the fault is diagnosed, especially on slippery or uneven surfaces.
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.