U0001: High speed CAN communication bus
A control module has found a fault on the high-speed CAN bus, the network the engine, gearbox, ABS and other modules use to talk to each other.
Updated
What U0001 means
A modern car’s control modules share data over a network, the CAN bus: the engine computer, the gearbox, the ABS and stability control, the instrument cluster and more. The high-speed CAN bus carries the data that has to arrive quickly.
U0001 means a module has found a fault on that bus itself, for example a broken or shorted wire, rather than one module that doesn’t answer. Codes that start with U are network codes; U0 codes are generic, the same on every car.
Read My Car reads the codes that the engine computer and, on many cars, the gearbox module report over generic OBD2. The ABS, airbag and body modules store their own network codes, which need a tool for your make.
Can I keep driving?
Drive gently
Drive gently and only as far as you need to, and have it checked soon. Modules may not get each other’s data, so the engine or gearbox can go into limp mode and ABS or stability control may be off; on some cars the engine can stall or not start. If several warning lights are on or the car behaves oddly, don’t drive on: have it recovered.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
If several warning lights are on at once or the car behaves oddly, don’t drive on: the modules may not be getting the data they need, including the ABS and stability control.
Symptoms
- Several warning lights at once, such as check engine, ABS, stability control and gearbox.
- Limp mode, odd gear changes, or gauges that freeze.
- On some cars, the engine won’t start.
Common causes
- Wiring or connector fault on the bus: a broken, chafed or shorted wire. Look for damage near earlier repairs, and for water in connectors.
- A faulty module that disturbs the bus. One failed module can disturb the whole bus. A garage finds it by disconnecting modules one at a time.
- Low battery voltage or a poor earth. Modules can drop off the bus when the voltage is low, so check the battery first.
Typical fixes
- Check the battery and its connections: a weak battery can cause network codes in several modules.
- Read all codes, and note which modules report network faults: they point to the part of the bus that’s affected.
- Have the bus wiring measured and checked for damage and water. A garage can disconnect modules one at a time to find one that disturbs the bus.
- Clear the codes after the repair, and read them again after a drive.
Questions
Can I drive with U0001?
Gently and only as far as you need to, and have it checked soon. The engine or gearbox can go into limp mode and ABS or stability control may be off; on some cars the engine can stall or not start. If several warning lights are on or the car behaves oddly, don’t drive on: have it recovered.
What does a U code mean?
Codes that start with U are network codes: a module lost contact with another one, or found a fault on the network. Those that start with U0 are generic and mean the same on every car; U1 and U2 codes are specific to the make.