What does it mean?
U1218 is a Network (CAN bus, module communications) fault code. It indicates: Manufacturer-Specific CAN/Network Bus Fault . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- Bulb-out warning displayed although every lamp works, or no warning when a bulb really has failed
- Some exterior lamps do not light, or light dimly
- Lamps flicker or change brightness with engine speed
- Lighting warning message on the driver information display
- Interior or ambient lighting misbehaving at the same time
- Additional network codes stored in the body module
Likely causes
- Blown exterior bulb, or a bulb of the wrong wattage, so the lamp monitor reads an implausible current
- Corroded bulb holder or lamp socket adding resistance to the lighting circuit
- Water inside a rear lamp assembly corroding the connector
- The lighting or body module loses power, ground or bus connection and stops broadcasting lamp status
- Damaged wiring in the tailgate or door harness where it flexes every time it is opened
- LED retrofit bulbs drawing too little current for the outage monitor to recognise
- Trailer wiring or a faulty towing module loading the lamp circuits
How to fix it
- Walk around the vehicle with a helper and operate every exterior lighting function
- Read the lighting module data and compare the reported lamp state with what you actually see
- Pull the suspect bulbs and check for the correct type, blackened glass and burnt contacts
- Clean or replace corroded sockets and check the ground point of each lamp cluster
- Flex the tailgate or door harness while watching live data for dropouts
- Remove any LED retrofit bulbs and retest with the specified bulbs
- Verify power, ground and bus connection at the lighting module before replacing it