U0078 code meaning
Control Module Communication Bus F Off
What U0078 means
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.
U0078 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0078
- Interior lamps or liftgate inoperative
- Radio, climate panel or cluster go blank
- Intermittent no-crank
Common causes of U0078
- Most likelyWater intrusion and corrosion in a body harness connector
- PossibleLow-speed bus wire pinched behind trim or headliner
- PossiblePoor ground of the body control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus f wiringCAN transceiver
What each part of U0078 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 78 | The exact fault in that area. |
What to do next
- Note U0078 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 U0078
What does U0078 mean?
U0078 means "Control Module Communication Bus F Off". At GM the bus behind U0078 is often the single-wire low-speed GMLAN that ties body modules together. It is a generic code, so it means the same on every make.
Is it safe to drive with U0078?
U0078 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0078 fail an emissions test?
U0078 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 U0078 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U0078 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.