U0242 code meaning
Lost Communication With Headlamp Control Module B
What U0242 means
Many cars fit one control module per headlamp, and the second one carries letter B. Jaguar labels the pair HCMA and HCMB on the 2020 XE (SSM74402), Bentley addresses them as light control left and right on the Continental GT (campaign 2056293/1), and a 2024 scan-tool release lists an HCMB for the Land Rover Discovery Sport. Which side B serves is not published. U0242 itself appears in no maker document; a receiver such as the body controller or gateway records it when the expected frames from B are missing. Because the two units share fuses, grounds or a bus branch on many cars, U0241 and U0242 stored together point to that common part rather than to two dead modules. The driver sees a lighting warning and the B-side lamp limited to basic functions. Data errors from B are U0543.
U0242 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0242
- Lighting warning in the cluster
- Headlamp on one side without adaptive or LED functions
- Daytime running or position light out on one side
Common causes of U0242
- Most likelyModule B without power or ground, e.g. blown fuse or loose lamp connector
- PossibleFault in a fuse, ground or bus branch shared with module A
- PossibleHeadlamp replaced without programming or with mismatched software
- Less likelyModule B internally faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Headlamp module bCAN bus
What each part of U0242 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 42 | The exact fault in that area. |
What to do next
- Note U0242 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0242
What does U0242 mean?
U0242 means "Lost Communication With Headlamp Control Module B". Many cars fit one control module per headlamp, and the second one carries letter B. It is a generic code, so it means the same on every make.
Is it safe to drive with U0242?
U0242 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0242 fail an emissions test?
U0242 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0242 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0242 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.