U0030–U0069 Vehicle Communication Bus A (+) Open
One of the data network's wires is broken, so the modules on it can no longer talk to each other properly. Check the network wiring and connectors.
Can you drive it? This is a communication fault on the car's data network. What it affects depends on the modules involved - a silent engine or gearbox module can bring on warning lights and limp mode, a comfort module only its own features. Check the power, earth and connector of the module named in the code, or the network wiring, first.
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 |
|---|---|---|
U0030 | Vehicle Communication Bus A (+) Open | Investigate soon |
U0033 | Vehicle Communication Bus A (-) Open | Investigate soon |
U0039 | Vehicle Communication Bus B (+) Open | Investigate soon |
U0042 | Vehicle Communication Bus B (-) Open | Investigate soon |
U0048 | Vehicle Communication Bus C (+) Open | Investigate soon |
U0051 | Vehicle Communication Bus C (-) Open | Investigate soon |
U0057 | Vehicle Communication Bus D (+) Open | Investigate soon |
U0060 | Vehicle Communication Bus D (-) Open | Investigate soon |
U0066 | Vehicle Communication Bus E (+) Open | Investigate soon |
U0069 | Vehicle Communication Bus E (-) Open | Investigate soon |
The definition
U0030: Vehicle Communication Bus A (+) Open.
U0030 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:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
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 your engine ECU's fault codes and the live measuring blocks behind them, and clears the codes once you have fixed the fault. On the engine it also does what a generic OBD reader cannot on a VAG: coding, adaptations, and Stage 1–3 flashing on Bosch ME7 petrol ECUs, with a backup saved every time it reads your ECU.
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Common questions
What does U0030 mean?
U0030 means Vehicle Communication Bus A (+) Open. One of the data network's wires is broken, so the modules on it can no longer talk to each other properly. Check the network wiring and connectors.
Can I drive with U0030?
This is a communication fault on the car's data network. What it affects depends on the modules involved - a silent engine or gearbox module can bring on warning lights and limp mode, a comfort module only its own features. Check the power, earth and connector of the module named in the code, or the network wiring, first.