What does this code mean?
The wording below belongs to the named make and communication. Match the complete code, reporting module, model year and engine before applying it.
A code identifies a detected condition, not a part that must automatically be replaced.
Manufacturer wording
Source wording can vary by vehicle and suffix. It is shown as written, not as a universal diagnosis.
U18B4Lost Communication with Radio on Ethernet Bus from happening againManufacturer communications
2Original wording in English
CHEVROLET, GMC
Reported code forms U18B4
This Technical bulletin provides a Correction for a Condition of OnStar Red LED Illuminated - DTCs U18B4, U18B5, U18AF Set.
GMC
Reported code forms U18B4
This technical bulletin provides a procedure to repair a bad terminal and re-route the harness to prevent the future event of Radio Audio Randomly Cuts Out DTC U18B4 - Lost Communication with Radio on Ethernet Bus from…
Check vehicle applicability
5A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Can I keep driving?
A code alone cannot establish whether driving is safe. A flashing malfunction light, severe shaking, overheating, oil-pressure warning or loss of braking or steering needs prompt attention. Stop in a safe place and seek assistance when control or engine safety is affected. Follow the vehicle handbook.