Chassis, generic

C00A4 Driveline Control Module Rear Differential Unit B Control Circuit Driver

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Where a rear unit carries a second actuator, for example the second clutch of a twin-clutch module that can drive each rear wheel on its own, the driveline module needs a second output stage, and C00A4 reports a fault in that one. If actuator B is a brushless motor, the stage is a three-phase bridge: automotive gate drivers such as TI's DRV8343-Q1 detect short to battery, short to ground, MOSFET overcurrent and gate driver faults, and offer an offline open-load and short check before the motor is switched on. BorgWarner's latest AWD coupling uses exactly such a brushless motor with integrated electronics. A driver fault on side B leaves actuator A usable, so some systems can keep partial AWD. No manufacturer publishes a C00A4 case; the actuator's own codes are C0097 and C0098.

Likely causes

Phase or supply line of actuator B shorted to ground or battery
Winding fault or blocked rotor in actuator B causing overcurrent
Failed output stage B in the module

Symptoms

  • AWD or torque vectoring warning
  • One rear clutch or locking function inactive

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,300
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

driveline modulerear diff actuator b

Related codes

C00A1C00A3C0097C0098

References: ti.com, borgwarner.com, just-auto.com.