U0001 means High Speed CAN Communication Bus. A module has detected a fault on the high-speed CAN network that the engine, transmission, brakes and other modules use to talk to each other. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What U0001 means
Modern vehicles have many control modules that share information over a network, usually called the CAN bus. Codes starting with U mean a module has stopped hearing another one, and voltage and processor codes mean a module is not getting clean power or has an internal fault. Low battery voltage, poor grounds, blown fuses and damaged wiring cause many of these codes, so test the battery and charging system first.
U0001 symptoms
- Several warning lights at once
- No start or stalling
- Many U-codes stored in different modules
Common causes of U0001
- Network wiring shorted or open
- A failed module disrupting the network
- Water in a network connector
- Low battery voltage
How to diagnose U0001
- Check battery voltage and grounds
- Measure network resistance at the diagnostic connector with the battery disconnected
- Unplug modules one at a time to find one disrupting the bus
Can you drive with U0001?
It depends on the symptoms; with multiple warning lights, have it checked before driving far.
U0001 tips
A healthy high-speed CAN bus usually reads about 60 ohms between the two network wires at the diagnostic connector with the battery disconnected; readings far from that point to a wiring or terminating-resistor problem.
Will U0001 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing U0001 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| U0100 | Lost Communication With ECM/PCM A |
| U0101 | Lost Communication With TCM |
| U0073 | Control Module Communication Bus A Off |
Guides that help
When it is more than a sensor
Voltage and network codes come from wiring, the battery, the charging system or a module, not from engine or transmission wear. If a lost-communication code has left the transmission in limp mode, rule out the module and wiring before deciding the unit has failed, and see our transmissions only if testing confirms internal damage.
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