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U031C Software Incompatibility With Brake System Control Module B

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

In GM's hybrid OBD tables brake system control module B is the electromechanical brake booster (Bosch iBooster), which builds brake pressure without engine vacuum and works hand in hand with the stability control unit. The 2016 to 2019 tables describe the check behind U031C: the stability module receives a compatibility index from the booster over CAN and compares it with its own configuration. If the index stays incompatible for 0.1 s, the code is stored, provided supply voltage is between 7.5 and 16 V, the bus is active and 5 s have passed after a power mode change. GM classes it as Type A: the warning lamp comes on during the very first drive with the fault. U01B4 is lost contact, U04B5 invalid data from module B, U0318 concerns the main brake module. Expect brake warnings and possibly reduced electric boost.

Likely causes

Brake booster unit replaced or swapped without programming to the vehicle
Stability control module updated or configured for another booster variant
Programming interrupted, for example by low battery voltage

Symptoms

  • MIL on and brake or stability warning in the cluster
  • Changed pedal feel or reduced electric brake boost
  • Code appears right after brake booster or ESP module work

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–900
Time0.5–2.5 h

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

Parts involved

brake system module bcontrol module software

Related codes

U01B4U04B5U0318U0315

References: gsi.ext.gm.com, gsi.ext.gm.com, bosch-mobility.com.