U0242 on 2005-2009 Buick LaCrosse — Lost Communication With Headlamp Control Module "B"
1 vehicles · 1 makes
Most Reported On
U0242 is an OBD-II diagnostic trouble code meaning “Lost Communication With Headlamp Control Module "B".” A controller is no longer receiving the periodic data-bus messages expected from Headlamp Control Module B (the opposite-side or secondary headlamp controller). Set after a calibrated timeout, it indicates lost communication with that lighting module. This code is most commonly reported on 2005-2009 Buick LaCrosse.
Common Causes
Diagnostic Tools
This is a network/communication code. A basic engine-code reader will not show it — you need a scanner that reads all modules. These read U0242.
One caveat that applies to every scanner: only powertrain codes are standardised across manufacturers. Body, chassis and network coverage is "enhanced" diagnostics, and how deep it goes varies by make and model year — check your specific vehicle against the tool's coverage list before buying.
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level tablet with all-system coverage and bi-directional control, so you can command a module rather than only read it.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
What you can do yourself, and what needs a shop
Reading the code, clearing it, and watching whether it returns is a driveway job with the right scanner. These steps are not:
- Module programming or software updates — needs the manufacturer software or a J2534 pass-through with a paid subscription.
- Replacing a control module — most are VIN-programmed and immobilizer-registered, so a new one does nothing until it is coded to your car.
- Airbag/SRS component work — a stored fault can deploy a live device.
If the vehicle is still under warranty, check for an open recall or technical service bulletin before buying anything — the repair may already be covered.
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FAQ
What does U0242 mean?
U0242 stands for "Lost Communication With Headlamp Control Module "B"." A controller is no longer receiving the periodic data-bus messages expected from Headlamp Control Module B (the opposite-side or secondary headlamp controller). Set after a calibrated timeout, it indicates lost communication with that lighting module.
What are the most common causes of U0242?
The most common causes of U0242 are: Power/ground loss to the headlamp control module, Open/shorted bus wiring, Corroded/loose connectors, Failed headlamp control module/ballast driver, Network fault. The specific cause varies by vehicle.
How much does it cost to fix U0242?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by U0242?
Au7o has documented U0242 across 1 vehicle models from 1 manufacturers: Buick.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.