NetworkU0040
SeriousSeverity: Serious - have it checked soon
Vehicle communication bus B (+) low
Key terms: Control module: a small computer that runs one part of the car
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 22
| Brand | Code | Description | System |
|---|---|---|---|
| Ashok Leyland CV | U0040 | SUCCESSFUL Brand | Network |
| BAIC Motor | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| BYD | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| Chery | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| Daewoo | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| DFFS | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| DFFX | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| DFXK | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| EOBD | U0040 | Sõiduki sidebuss B (+) madal Brand | Network |
| Geely | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| GM | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| Great Wall | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| Hafei | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| Hyundai | U0040 | No description available | Network |
| Land Rover | U0040 | Vehicle communication bus B(+) low Brand | Network |
| Maserati | U0040 | LIN bus circuit low Brand | Network |
| Mitsubishi | U0040 | No description available | Network |
| Peugeot | U0040 | No description available | Network |
| Saab | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| MG (SAIC) | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| Tata | U0040 | Vehicle Communication Bus B (+) Low Brand | Network |
| Toyota | U0040 | Vehicle communication bus B (+) low 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.
5Extended variant codes 2
These 7-character codes are manufacturer-specific variants of U0040 and may be reported by some scan tools.
6Related codes
Browse Uxxx codes or U004xx codes.