U0073Control Module Communication Bus A Off
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- U0073 is logged by a module whose own CAN controller has withdrawn from Bus A. Each failed transmission adds eight to its transmit error counter; above 255 the chip goes bus off and may rejoin only after 128 runs of 11 recessive bits (onsemi). GM's 2019 tables flag more than five bus-off events, about 0.06 s, inside a 0.81 s window as Type A with MIL on the first trip, and the ECM suspends lost-communication tests such as U0101 while it is active. Around 2006 GM still reported this state as U0001. A Ford TCM turns the MIL on at once because engine speed is missing. Bulletins trace U0073 to a loose ground (Trax, G103), backed-out terminals in the 6L80 transmission connector and harness rubbing on a cylinder head (Silverado LV3). Expect several warnings, possibly a gearbox held in one gear.
- What you may notice
- MIL and several cluster warnings at the same time
- Transmission stuck in one gear or shifting harshly
- Gauges fluctuate or drop out briefly
- Lost-communication codes such as U0100 or U0101 in other modules
- Likely causes
- LikelyBus A wires chafed through or shorted to ground in the harness
- PossibleLoose or corroded ground point of a module on Bus A
- PossibleBacked-out or loose terminals, e.g. in the transmission connector
- RareOpen or shorted terminating resistor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.