C00A4 code meaning
Driveline Control Module Rear Differential Unit B Control Circuit Driver
What C00A4 means
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.
C00A4 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C00A4
- AWD or torque vectoring warning
- One rear clutch or locking function inactive
Common causes of C00A4
- Most likelyPhase or supply line of actuator B shorted to ground or battery
- PossibleWinding fault or blocked rotor in actuator B causing overcurrent
- Less likelyFailed output stage B in the module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Driveline moduleRear diff actuator b
What each part of C00A4 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| A4 | The exact fault in that area. |
What to do next
- Note C00A4 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C00A4
What does C00A4 mean?
C00A4 means "Driveline Control Module Rear Differential Unit B Control Circuit Driver". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with C00A4?
Drive gently and only to a workshop. With C00A4 the car can go into limp mode (reduced power) to protect itself.
Will C00A4 fail an emissions test?
C00A4 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C00A4 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will C00A4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.