Network, generic

U0028 Vehicle Communication Bus A

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0028 is the general code for Vehicle Communication Bus A, a neutral label each maker assigns to a network of its choosing. GM uses it in the radio of many 2013-19 models as the health indicator of the MOST infotainment ring, which the radio masters: a current U0028 symptom 00 points to a MOST module with a power, ground or wake-up fault, found by bypassing modules with kit EL-51578 until the code turns to history. In the 2026 Tahoe/Escalade family the brake control module stores U0028-88, whose diagnostic path is swapped with U0037-88 by a software slip. Audi assigns Bus A to the sensor/hybrid CAN of its 48 V mild hybrids and lists U002800 on the Q5 PHEV after a chafed power-electronics harness. Isuzu N-Series trucks show it with a misconfigured FMS-CAN interface.

Likely causes

Power, ground or wake-up fault at a module on the bus (GM MOST ring)
Bus or supply wiring chafed or pinched (Audi Q5 PHEV, GM dash harness)
Connectors not fully seated or locked, spread pins
Wrong module configuration or software fault (Isuzu FMS, GM brake module 2026)

Symptoms

  • Infotainment functions dead: blank radio display, no audio, steering wheel controls inoperative (GM)
  • Battery or electrical system warning in the cluster (Audi mild hybrid)
  • Several warning lamps, vehicle may not be drivable (Audi Q5 PHEV)
  • Further communication codes stored alongside

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–1,200
Time0.5–6 h

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

Parts involved

bus a wiringcontrol moduleinfotainment module

Related codes

U0001U0029U0030U0036U0037

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.