U018A: Lost Communication With Headlamp Leveling Control Module B

What it means

ECU lost communication with headlamp leveling control module B (auto-levelling for HID/LED headlamps).

At a glance

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

How it works

Headlamp leveling control module B controls automatic aim adjustment for the headlamp system assigned to module B, often as part of an HID or LED setup. U018A is stored when the ECU stops receiving the expected network messages from module B for the specified time. A loss of module power or incorrect gateway routing can cause this; a CAN termination fault should be tested to the vehicle manufacturer's specification rather than assumed from a generic resistance value.

Common causes

Most likely first.

1. Module unpowered
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Headlamp leveling functions may be unavailable or impaired
• Other communication codes

How to diagnose it

1. Scan all modules and review freeze-frame data and network codes to determine whether the loss is limited to headlamp leveling module B or affects the wider CAN network.
2. Check headlamp warnings and observe whether the lamps assigned to module B adjust as expected during the vehicle's normal self-check, if equipped.
3. Inspect module B's connector, power and ground wiring, and CAN harness for corrosion, moisture, or damage.
4. Verify module B's power and ground under manufacturer-specified test conditions.
5. Test CAN communication, including network termination if directed by the wiring diagram, against the manufacturer's specifications.
6. If supplies and network pass, check gateway routing and evaluate module B with vehicle-specific diagnostics before replacement.

Common fixes

• Restore battery voltage or repair a confirmed power supply fault.
• Clean, secure, or repair the headlamp leveling module B connector.
• Repair damaged power, ground, or CAN wiring to module B.
• Correct a verified gateway routing or CAN termination fault to the manufacturer's specification.
• Replace or configure module B only after its supplies and network communication have been verified.

Can I keep driving?

The vehicle may be driveable, but the headlamps assigned to module B may not self-level, which can reduce visibility or dazzle other road users. Avoid night driving if their aim is clearly wrong, and have the leveling system checked promptly.