Network, generic

U015A Lost Communication With Anti-Lock Brake System (ABS) Control Module B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U015A concerns a second anti-lock brake controller, module B. Vehicles prepared for automated driving need braking that still works after a single fault, so suppliers pair two independent units, for example Bosch's iBooster with the ESP control unit. If the partner that monitors module B, typically the primary brake controller or the driving automation computer, no longer receives its periodic messages, U015A is stored. No manufacturer documents this code publicly; the setting idea follows GM's generic rule for lost-communication codes (supervised message missing at 9-16 V). U0121 is ABS module A, U045B flags implausible data from B. Expect a brake or assistance warning and blocked automated functions.

Likely causes

Brake module B without power or ground (own fuse in redundant layouts)
Bus line or connector to module B in the engine bay corroded or open
Brake modules on incompatible software after repair
ABS control module B internally faulty

Symptoms

  • Brake system or driver assistance warning in the cluster
  • Automated driving or adaptive cruise functions unavailable
  • Code stored in the primary brake controller

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–2,500
Time0.5–4 h

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

Parts involved

abs module bcan bus

Related codes

U0121U045BU031CU0129U015B

References: law.cornell.edu, us.bosch-press.com, saabwisonline.com.