What it means
The driveline control module monitors its driver for rear differential unit B and sets this code when the driver detects a fault controlling that unit.
How it works
The driveline control module uses an electronic driver to control rear differential unit B, a separate controlled unit from rear differential unit A. The module checks unit B's control circuit as it commands that component. An electrical fault in the unit B circuit or driver can set C00A4 and restrict AWD operation.
Common causes
Most likely first.
- Open or short in rear differential unit B control circuit
- Damaged wiring or connector
- Power or ground fault
- Driveline control module driver fault
Symptoms
- AWD or 4WD warning
- AWD may be unavailable or limited
How to diagnose it
- Read driveline-module codes and freeze-frame data to establish when the rear differential unit B circuit fault occurred and whether supply-related faults were logged.
- Review live data for the command and status of rear differential unit B, if available, and compare it with the requested drive mode.
- Inspect the unit B connector and harness for corrosion, loose terminals, chafing, or damage near the rear differential.
- Check the module and unit B power and ground connections according to the manufacturer's procedure.
- Trace and test the unit B control circuit for opens or shorts using the vehicle wiring diagram, comparing results with the manufacturer's specification before blaming the module driver.
Common fixes
- Clean and secure the rear differential unit B connector.
- Repair damaged wiring or terminals in the unit B control circuit.
- Correct a verified power or ground fault.
- Replace rear differential unit B only if testing confirms an internal component fault.
- Replace or reprogram the driveline control module only after confirming its unit B driver has failed.
Can I keep driving?
AWD may be limited or unavailable, so do not count on it for low-traction conditions or difficult terrain. Stop if there is driveline binding, unusual noise, or a change in the vehicle's ability to move.
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.