Fault Family System: Network (U-Codes) 13 SAE Codes

CAN Bus Off Fault

Diagnostic & Technical Explanation

U0073 means a CAN controller has counted enough consecutive transmit errors to trip its bus-off protection and disconnect itself from the network entirely -- a controller-state fault, not a simple wiring open -- and it is almost always triggered by one specific module flooding the bus with corrupt frames or holding a line dominant. Because a healthy module can appear to be at fault just for reporting bus-off after another module misbehaves, the repair path is a half-split isolation test (unplug modules one at a time and watch for the bus to recover) rather than a blind wiring check. A dead-shorted CAN wire or a module stuck transmitting during a software hang are the two most common root causes.

These 13 diagnostic trouble codes share one detection mechanism and one repair path, which is why MechanicDB groups them into a single authored fault family rather than repeating the same explanation 13 times.

Codes in this family (13)

Code	Definition	Repair coverage
U0073	Control Module Communication Bus A Off	4 ranked fixes
U0074	Control Module Communication Bus B Off	4 ranked fixes
U0075	Control Module Communication Bus C Off	4 ranked fixes
U0076	Control Module Communication Bus D Off	4 ranked fixes
U0077	Control Module Communication Bus E Off	4 ranked fixes
U0078	Control Module Communication Bus F Off	4 ranked fixes
U0079	Control Module Communication Bus G Off	4 ranked fixes
U007A	Control Module Communication Bus H Off	4 ranked fixes
U007B	Control Module Communication Bus I Off	4 ranked fixes
U007C	Control Module Communication Bus J Off	4 ranked fixes
U007D	Control Module Communication Bus K Off	4 ranked fixes
U007E	Control Module Communication Bus L Off	4 ranked fixes
U007F	Control Module Communication Bus M Off	4 ranked fixes

What this page does not show

This page publishes the fault mechanism and the code index. The licensed dataset adds, for every one of the 15,886 codes, the full authored repair set (56,729 procedures in total) with the fields deliberately withheld here:

Procedures 2..n after the first-listed procedure
Aftermarket parts cost ranges in USD (est_parts_cost_min/max_usd)
Professional labor-hour estimates (est_labor_hours)
Step-by-step diagnostic and repair instructions
Replacement-part mappings and catalog lookups
6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)

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