U0077 code meaning
Control Module Communication Bus E Off
What U0077 means
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.
U0077 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0077
- Service ABS, StabiliTrak or power steering messages
- Suspension or all-wheel-drive warnings
- Heavy steering when the steering module drops off
Common causes of U0077
- Most likelyCorroded underbody connector in the Bus E harness
- PossibleHigh resistance in the communication enable (wake-up) circuit
- Less likelyOne-off software event in a module, cleared without repair
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus e wiringCAN transceiver
What each part of U0077 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 77 | The exact fault in that area. |
What to do next
- Note U0077 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0077
What does U0077 mean?
U0077 means "Control Module Communication Bus E Off". At GM, Bus E is usually a chassis-side network. It is a generic code, so it means the same on every make.
Is it safe to drive with U0077?
Drive gently and only to a workshop. With U0077 the car can go into limp mode (reduced power) to protect itself.
Will U0077 fail an emissions test?
U0077 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0077 to fix?
Difficulty: hard. A typical repair takes 0.5 to 5 hours of work. This is a job for a workshop.
Will U0077 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.