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U0242 Lost Communication With Headlamp Control Module B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Module B without power or ground, e.g. blown fuse or loose lamp connector
Fault in a fuse, ground or bus branch shared with module A
Headlamp replaced without programming or with mismatched software
Module B internally faulty

Symptoms

  • Lighting warning in the cluster
  • Headlamp on one side without adaptive or LED functions
  • Daytime running or position light out on one side

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,200
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

headlamp module bcan bus

Related codes

U0241U0543U0542

References: static.nhtsa.gov, static.nhtsa.gov, oemtools.com.