Network, generic

U012B Lost Communication With Chassis Control Module B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U012B is the counterpart to U012A for a second chassis controller, labelled B. No manufacturer documents U012B in an openly available source, so its exact job (air suspension, damping, steering or another chassis task) depends on the vehicle. Logic follows the usual network rule that CARB requires and GM spells out for module A: a receiving controller expects a periodic message, and if it stays away for a calibrated time while supply and ignition are valid, the receiver stores the code for the silent partner. GM's tables for U012A list Type B on engine nodes and Type C on the transmission, so the warning lamp behaviour is maker specific. Invalid data from module B is U042C.

Likely causes

Fuse, power or ground of chassis module B interrupted
Damaged bus line or connector to module B
Chassis module B internally faulty or not programmed

Symptoms

  • Chassis warning message in the cluster
  • Functions handled by module B (e.g. suspension) unavailable
  • Scan tool cannot reach module B

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–1,500
Time0.5–4 h

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

Parts involved

chassis module bcan bus wiring

Related codes

U042CU012A

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com.