What it means
The driveline control module monitors its driver for rear differential unit A 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 A, which may be an actuator or other controlled component depending on the vehicle. It checks the unit A control circuit while commanding that component. An electrical fault in this circuit or its driver can set C00A3 and limit AWD operation.
Common causes
Most likely first.
- Open or short in rear differential unit A 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 identify when the rear differential unit A circuit fault occurred and whether related power or ground codes are present.
- Check live data for the command and reported status of rear differential unit A, if supported, and note whether the fault appears during a mode change.
- Inspect the unit A connector and nearby harness for corrosion, loose pins, water entry, or rubbing damage.
- Check driveline control module and unit A power and ground connections using the manufacturer's procedure.
- Use the vehicle wiring diagram to test the unit A control circuit for opens or shorts, then compare readings with the manufacturer's specification before condemning the module driver.
Common fixes
- Clean and secure the rear differential unit A connector.
- Repair damaged or corroded wiring in the unit A control circuit.
- Repair a verified power or ground fault.
- Replace the rear differential unit A component only if its own fault is confirmed.
- Replace or reprogram the driveline control module only after its unit A driver is confirmed faulty.
Can I keep driving?
AWD may be limited or unavailable; avoid relying on it for slippery surfaces or demanding terrain. If the vehicle develops driveline binding, abnormal noise, or loss of drive, stop and have it checked.
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.