OBD2 code 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.
Detected Root Component
Network Component
Observed Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Possible Causes
- CAN line shorted to supply or ground
- Terminating resistor failed
- Gateway module routing CAN messages incorrectly
Tools Required
Interactive Diagnostic
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Parts likely to be the cause (Moteur (général))
Moteur (général)
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Frequently asked questions about code U0040
What does code U0040 mean? ▾
OBD2 code 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.
What are the symptoms of code U0040? ▾
Code U0040 may cause: Multiple warning lights may illuminate, Affected modules may go into limp mode or shut down, Specific functions inoperative depending on module, Diagnostic tools may show communication faults. The intensity of these symptoms varies depending on the vehicle and driving conditions.
What causes code U0040? ▾
The most common causes of code U0040 are: CAN line shorted to supply or ground, Terminating resistor failed, Gateway module routing CAN messages incorrectly. A proper OBD2 diagnostic will pinpoint the exact cause.
Is it serious to drive with code U0040? ▾
Yes, code U0040 is critical (Critical). Avoid driving and consult a professional promptly to prevent major damage.
How do I fix code U0040? ▾
Start by reading the code with an OBD2 scanner, then follow the interactive decision tree on this page. Priority causes to check: CAN line shorted to supply or ground, Terminating resistor failed, Gateway module routing CAN messages incorrectly. Difficulty: Medium · Estimated time: 30-60min.