Code result
U0040
Communication Bus Off
High severity
What it means
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.
Is it safe to drive?
No — stop driving
This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly.
Most likely causes
CAN line shorted to supply or ground
highOne of the most commonly reported causes for this code — check this first.
Terminating resistor failed
mediumA plausible cause — test and verify before replacing parts.
Gateway module routing CAN messages incorrectly
lowLess common, but worth ruling out after the more likely causes.
Related help
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