U0002 U0xxx · Network (U) Medium severity
High Speed CAN Communication Bus Performance
The bus still works but with errors, retries or degraded signal quality. Far more common than a total bus failure and much harder to spot.
Severity guidance: Medium — drivability or emissions affected, book it in this week
Symptoms you will notice
- Intermittent warning lamps
- Random module dropouts
- Faults that clear themselves
Common causes
Ordered from most to least likely — start at the top.
- 1 Corroded or loose connector terminal
- 2 Aftermarket equipment teed into the bus
- 3 Water ingress in a junction connector
- 4 Marginal earth raising noise
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Check for recently fitted aftermarket equipment first — trackers, alarms and audio interfaces are frequent culprits.
- ✓ Wiggle the harness while watching for bus errors.
- ✓ Inspect junction connectors for moisture.
- ✓ Scope for ringing or a collapsed recessive level.
Repair options
- Remove or correctly interface aftermarket equipment
- Clean and reseat connectors
- Repair the affected wiring section
U0002 — frequently asked questions
Why does it only happen in the rain? +
Water in a connector changes bus capacitance. Find the wet junction and seal it.
Can a tracker really break the bus? +
Yes. Anything teed into CAN without proper interfacing distorts the signal.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.