Network, generic

U0129 Lost Communication With Brake System Control Module A

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0129 points to the brake system control module A, in GM vehicles the OBD node with diagnostic ID 7E5. GM's 2019 LTG engine table checks frames $0C1, $0C5, $0D1, $1C6 and others every 500 ms (one of them 10 s) and needs two trips to set the MIL; the 2018 hybrid controller and the 2025 ECM treat it as Type A, the 2017 table as Special Type C. Stellantis calls the partner Brake System Control Module 1. GM N192267870 adds a software case: after a jump start the 2019 Silverado ECM stored U0129 with U0101/U0140 and lit the service engine lamp. U0121 covers the ABS module, U0418 invalid brake data. Brake assist and stop-start may be reduced.

Likely causes

Fuse, supply or ground of the brake control module faulty
Low battery or jump start leaving stored network codes (ECM update released)
Damaged or corroded CAN wiring to the brake module
Brake system control module internally faulty

Symptoms

  • MIL or service engine lamp plus brake/ESC warnings
  • Gear selection or stop-start blocked on some vehicles
  • Several other U codes stored at the same time

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–1,800
Time0.5–4 h

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

Parts involved

brake system control modulecan bus wiring

Related codes

U0318U0418U0121U0128U0122

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.