C009B4WD/AWD Rear Differential Unit Actuator A Position Sensor C
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- C009B covers the third position channel, C, of actuator A in the rear differential unit. With A and B intact the module can still see motion, so a fault on C is caught by comparing edges: a Woodward patent identifies the failed sensor as the one whose output stays constant between two invalid state combinations, roughly one electrical revolution apart, and then keeps the motor running on two sensors with a synthesised third signal at reduced torque. Whether an AWD module uses such a fallback is not published; most simply release the clutch. Schaeffler's clutch actuator patent places the Hall carrier on the stator so it can be swapped separately, though in many rear units the sensors sit inside the motor housing. No carmaker documents C009B publicly. Unlike C009C, this code blames one channel, not their combination.
- What you may notice
- AWD/4WD fault message
- All-wheel drive switched off for the rest of the trip
- Likely causes
- LikelyOpen circuit or short on the channel C signal line
- PossibleHall element C inside the actuator motor failed
- RareMoisture in the actuator connector at the rear axle
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,100
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.