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U012A Lost Communication With Chassis Control Module A

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U012A reports that chassis control module A is silent. The unit behind the letter A varies between brands; GM uses the code in several engine and transmission tables. The 2016 ECM for the L20 engine waits for message $4DB and logs a missing frame as Type B, so the MIL comes after two trips; the 2020 ten-speed transmission controller watches frame $1F7 from the integrated chassis control module (ICCM) and treats the loss as emissions-neutral Type C. GM's 2015 engine table even uses U012A for a lost fuel pump control module, more than 0.5 s without a message, also Type B. U012B is the B module, U042B invalid data from module A. Effects range from chassis warnings to engine trouble.

Likely causes

Power, ground or fuse of chassis module A missing
Bus wiring or connector to the module damaged
Voltage dip leaving a stored code
Chassis module A internally faulty

Symptoms

  • MIL on in vehicles where the engine controller logs it
  • Chassis functions controlled by module A unavailable
  • Hard start or stalling if the module drives the fuel pump

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 acan bus wiring

Related codes

U042BU012BU0073

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.