U0242: Lost Communication With Headlamp Control Module B

What it means

A control module has stopped receiving expected messages from headlamp control module B. The code identifies the communication loss; lighting functions controlled by the module may be affected.

At a glance

• Usually lights the warning light of the system that lost communication

How it works

Headlamp control module B operates the headlamp functions assigned to the B module and shares status and commands with other modules over the vehicle network. U0242 sets when expected messages from module B stop arriving, so functions handled by B may be limited or unavailable.

Common causes

Most likely first.

1. Loss of power or ground to the module
2. Open, shorted, or damaged network wiring or connector
3. Failed module

Symptoms

• One or more headlamp functions may be unavailable or limited
• A lighting warning may appear depending on the vehicle

How to diagnose it

1. Scan all modules for communication codes and review freeze-frame or event data for other faults on the network used by headlamp control module B.
2. Check the specific headlamp functions assigned to module B and record any lighting warnings or failures.
3. Inspect module B's connector and network wiring for corrosion, water intrusion, loose terminals, or physical damage.
4. Check module B's power and ground circuits according to the manufacturer's procedure to rule out a lost supply.
5. Test the network wiring to module B for an open, short, or poor connection using the wiring diagram.
6. If power, ground, and network tests pass, use the manufacturer's diagnostic procedure to confirm whether module B itself has failed.

Common fixes

• Reconnect or clean a loose or corroded module B connector.
• Repair damaged network wiring or terminals serving headlamp control module B.
• Restore power or ground to module B by repairing the affected supply circuit.
• Replace headlamp control module B if testing confirms an internal failure.

Can I keep driving?

Avoid night driving or poor visibility if the headlamp functions controlled by module B are reduced. Drive only if all required lighting works reliably, and stop using the vehicle if essential headlights fail.