NetworkU0021
SeriousSeverity: Serious - have it checked soon
Low Speed CAN Communication Bus (+) Open
Key terms: Control module: a small computer that runs one part of the car · SAE J2012: the standard generic code list
1What it means in plain English
Control modules in the car cannot communicate with each other over the vehicle network.
2Common causes
- Wiring or connector fault on the communication bus
- Faulty control module
- Low battery voltage or poor ground
- Water ingress in a connector or module
- Aftermarket device interfering with the bus
3Can I drive?
The car may run normally or may not run at all. If the module that has lost communication controls steering, brakes, park brake, charging or engine cooling, drive only if those systems feel normal; stop safely if the steering becomes heavy, a brake warning appears, or the engine temperature climbs. If the car will not start or runs badly, have it towed.
This page gives general information. It is not professional advice. For a definite diagnosis and a repair quote, ask a qualified mechanic to inspect the car.
4Brand data 25
| Brand | Code | Description | System |
|---|---|---|---|
| Ashok Leyland CV | U0021 | Low Speed CAN Communication Bus (+) Open SAE | Network |
| BAIC Motor | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Mercedes-Benz | U0021 | Low Speed CAN Communication Bus (+) Open SAE | Network |
| BYD | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Chery | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Daewoo | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| DFFS | U0021 | Vehicle speed fault Brand | Network |
| DFFX | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| DFXK | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| EOBD | U0021 | Low speed CAN communicatiebus (+) open Brand | Network |
| Geely | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| GM | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Great Wall | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Hafei | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Holden | U0021 | Low Speed CAN Bus [+ Brand | Network |
| Hyundai | U0021 | Low Speed CAN Communication Bus (+) Open SAE | Network |
| Land Rover | U0021 | Low speed CAN communication bus(+) open Brand | Network |
| Mitsubishi | U0021 | CAN-B bus (+) circuit open Brand | Network |
| Opel | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Peugeot | U0021 | Low Speed CAN Communication Bus (+) Open SAE | Network |
| Proton | U0021 | CAN-B bus (+) circuit open Brand | Network |
| Saab | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| MG (SAIC) | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Tata | U0021 | Low Speed CAN Communication Bus (+) Open Brand | Network |
| Toyota | U0021 | Vehicle speed fault Brand | Network |
Legend: SAE is the generic J2012 description; Brand is text taken from that manufacturer’s data. Manufacturer rows keep the wording and language of the source data, and non-English text is tagged so screen readers pronounce it correctly.
5Related codes
Browse Uxxx codes or U002xx codes.