U0040
Communication Bus Off
A control module has counted enough transmit errors to enter the bus-off state defined by ISO 11898 and stops transmitting on the bus. Multiple modules typically lose communication and several warning lamps illuminate at once.
A control module has counted enough transmit errors to enter the bus-off state defined by ISO 11898 and stops transmitting on the bus. Multiple modules typically lose communication and several warning lamps illuminate at once.
Common causes
- high
CAN line shorted to supply or ground
One of the most commonly reported causes for this code — check this first.
Typical part cost: $90-1650
- medium
Terminating resistor failed
A plausible cause — test and verify before replacing parts.
Typical part cost: $90-1650
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First things to check
- 1Confirm the code with a scan tool and check for additional related codes.
- 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.
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Related codes
See related trouble codes
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Frequently asked questions
What does U0040 mean?
U0040 means "Communication Bus Off". It is a generic OBD-II code that points to a fault in the network / communication.
What are the most common causes of U0040?
can line shorted to supply or ground; terminating resistor failed; gateway module routing can messages incorrectly — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.
Can I keep driving with this code?
This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly. Use the Wrenchify app for a full diagnosis specific to your vehicle.
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