Network, generic

U0078 Control Module Communication Bus F Off

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

At GM the bus behind U0078 is often the single-wire low-speed GMLAN that ties body modules together. Equinox and Terrain models from 2010 to 2015 set it with lost-communication codes for body module, cluster and liftgate when water corrodes connector X901 above the liftgate glass. On the 2013-16 Acadia the low-speed wire to the remote door lock receiver got pinched between the rear HVAC duct and the roof, giving intermittent no-crank, a dead radio and erratic gauges. A poor body control module ground at G218 on the 2015 Escalade produced U0078 together with U0073. Because these modules handle comfort and access, owners mostly notice dark interior lights, a dead liftgate or blank displays. GM's published OBD tables do not list U0078, so no MIL type is documented.

Likely causes

Water intrusion and corrosion in a body harness connector
Low-speed bus wire pinched behind trim or headliner
Poor ground of the body control module

Symptoms

  • Interior lamps or liftgate inoperative
  • Radio, climate panel or cluster go blank
  • Intermittent no-crank

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–600
Time0.5–4 h

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

Parts involved

bus f wiringcan transceiver

Related codes

U0073U0077U0080U0140U0155

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