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U018A Lost Communication With Headlamp Leveling Control Module B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U018A covers headlamp leveling control module B. Cars with separate levelling electronics in each headlamp, or with a central controller plus lamp-side units, need a second address; U0181 is the first module. The electronics set the beam angle from ride-height sensor data so that load or pitch does not dazzle oncoming traffic, which LED and xenon lamps usually require. No manufacturer documents U018A publicly, and it appears neither in GM's U-code list nor in the NHTSA bulletin index. The trigger is the same as for other lost-communication codes in GM's description: a periodic message missing at 9-16 V supply. Beam height on one side may freeze or drop to a low default, a lighting warning is possible, the MIL stays off. U048B is invalid data from B.

Likely causes

Levelling module B without power or ground
Corroded connector at the headlamp from moisture
Bus line to the headlamp damaged after a front-end repair
Headlamp levelling module B faulty or not coded

Symptoms

  • One headlamp no longer adjusts its beam height
  • Headlamp or lighting warning in the cluster
  • Uneven or very low beam pattern

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–900
Time0.5–3 h

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

Parts involved

headlamp leveling module bcan bus wiring

Related codes

U0181U048BU0180

References: saabwisonline.com, hella.com.