Network, generic

U0073 Control Module Communication Bus A Off

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U0073 is logged by a module whose own CAN controller has withdrawn from Bus A. Each failed transmission adds eight to its transmit error counter; above 255 the chip goes bus off and may rejoin only after 128 runs of 11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.

Likely causes

Bus A wires chafed through or shorted to ground in the harness
Loose or corroded ground point of a module on Bus A
Backed-out or loose terminals, e.g. in the transmission connector
Open or shorted terminating resistor

Symptoms

  • 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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–900
Time1–6 h

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

Parts involved

can bus wiringcan terminating resistorcontrol module

Related codes

U0001U0028U0074U0100U0101

References: gsi.ext.gm.com, newtonnet.co.uk, static.nhtsa.gov, static.nhtsa.gov.