OBD-II · Network and communication (U)
U0073
Control module communication bus A off
What it means
A control module has shut down its connection to data bus A because it could not communicate reliably on it.
Symptoms
- Multiple warning lights
- Intermittent no-start or limp mode
- Lost-communication codes in other modules
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | low 12V battery voltage or recent battery disconnection |
| 02 | CAN wiring short to ground/positive or between CAN-H and CAN-L |
| 03 | water-damaged or corroded connector |
| 04 | a faulty module on the bus |
| 05 | aftermarket device spliced into the network |
What to check, step by step
- 01Check the 12V battery and charging system; save a full scan before clearing codes
- 02Use OEM diagrams to identify bus A, missing modules and suitable test points; do not assume the diagnostic socket accesses that bus
- 03Inspect its wiring and connectors for water, corrosion and shorts
- 04Perform resistance tests only with the circuit de-energised as specified by the manufacturer; use the specified powered state for voltage or waveform tests
- 05Isolate branches or modules using the OEM shutdown procedure and account for removed terminators; follow SRS or high-voltage precautions as applicable