Network, generic

U0077 Control Module Communication Bus E Off

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

At GM, Bus E is usually a chassis-side network. In the 2018 tables for the LYX engine variant, the ECM watches it the same way as Bus A, more than five bus-off events within 0.81 s, but rates the result Type X without MIL; the transmission's default-to-park checks stay disabled while U0077 is set. On the 2015 Escalade, high resistance under the sill plates in circuit 5986, which wakes the modules for communication, left the brake, steering and suspension modules without a proper wake-up signal; on 2010-15 Equinox and Terrain models corrosion in connector X411 behind the fuel tank caused it. Volvo mild hybrids may store U007700 in the medium-voltage battery module together with P0A7B at pre-delivery; Volvo advises clearing it and reloading software only if it returns with MIL.

Likely causes

Corroded underbody connector in the Bus E harness
High resistance in the communication enable (wake-up) circuit
One-off software event in a module, cleared without repair

Symptoms

  • Service ABS, StabiliTrak or power steering messages
  • Suspension or all-wheel-drive warnings
  • Heavy steering when the steering module drops off

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–800
Time0.5–5 h

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

Parts involved

bus e wiringcan transceiver

Related codes

U0064U0074U0076U0078U0121

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