U0031–U0070 Vehicle Communication Bus A (+) shorted Low (to ground)
A wire in this circuit is touching the car's metal body, so current escapes to earth instead of reaching the part.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
U0031 | Vehicle Communication Bus A (+) shorted Low (to ground) | Investigate soon |
U0034 | Vehicle Communication Bus A (-) shorted Low (to ground) | Investigate soon |
U0040 | Vehicle Communication Bus B (+) shorted Low (to ground) | Investigate soon |
U0043 | Vehicle Communication Bus B (-) shorted Low (to ground) | Investigate soon |
U0049 | Vehicle Communication Bus C (+) shorted Low (to ground) | Investigate soon |
U0052 | Vehicle Communication Bus C (-) shorted Low (to ground) | Investigate soon |
U0058 | Vehicle Communication Bus D (+) shorted Low (to ground) | Investigate soon |
U0061 | Vehicle Communication Bus D (-) shorted Low (to ground) | Investigate soon |
U0067 | Vehicle Communication Bus E (+) shorted Low (to ground) | Investigate soon |
U0070 | Vehicle Communication Bus E (-) shorted Low (to ground) | Investigate soon |
The definition
U0031: Vehicle Communication Bus A (+) shorted Low (to ground).
U0031 is a network code (communication between control modules), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Unplug the connector at the part and measure resistance from each signal pin to a good earth. A healthy circuit reads open, not a few ohms.
- Follow the loom for chafe points - where it crosses a bracket, passes an edge, or flexes near a hinge or the engine mounts.
- Look for water or corrosion in the connector. A wet plug shorts pins to each other and to the body.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Prefer to work on your phone? The VAGPULSE Android app is a free download and its demo mode runs against a sample car with no hardware at all, so you can see exactly what it reads before spending anything. Reading your car with it needs the VAGPULSE cable, which comes with the licence.
Common questions
What does U0031 mean?
U0031 means Vehicle Communication Bus A (+) shorted Low (to ground). A wire in this circuit is touching the car's metal body, so current escapes to earth instead of reaching the part.
Can I drive with U0031?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.