What it means
The vehicle bus reports loss of communication with front radar module A. Adaptive cruise control, automatic emergency braking and forward collision warning lose their primary range/closing-speed input.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
Front radar module A measures distance and closing speed for forward-facing driver assistance functions. The vehicle monitors its network messages; U02B4 sets when module A stops communicating, removing its radar input from systems such as adaptive cruise control or automatic emergency braking.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan driver-assistance modules for network codes and review freeze-frame data to identify when front radar A stopped reporting.
- Check the dashboard for radar or collision-assistance warnings and note which forward-facing features are disabled.
- Inspect the front radar A area, connector, and accessible bus wiring for damage, looseness, or corrosion.
- Check the module's power and ground supply using the manufacturer's procedure.
- Test the network wiring to front radar A for an open, short, or poor connection.
- If wiring, power, and ground pass, follow the manufacturer's diagnostics to confirm whether front radar module A has failed.
Common fixes
- Reconnect or clean the front radar A connector.
- Repair damaged network wiring to front radar A.
- Restore the module's power or ground supply.
- Replace front radar module A if testing confirms it has failed, then perform any required manufacturer calibration.
Can I keep driving?
Do not rely on adaptive cruise control, forward collision warning, or automatic emergency braking while radar A communication is lost; these functions may be disabled or impaired. Drive manually with extra following distance and arrange repair promptly.
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.