CAN self-diagnosis is performed by each
ECU connected to the CAN bus.
Diagnosis codes related to communication are named with the capital letter U, and
are called "U-codes."
A summary of the CAN self-diagnosis system is presented below.
TIME-OUT
Each ECU transmits data frames periodically. If the data frame is not received within
the specified period, the intended receiving ECU transmits a diagnosis code indicating communication
time-out for the ECU that failed to transmit.
BUS OFF
Related to a communication error that persists even after the transmitting ECU attempts
recovery for a specified number of attempts or that persists for a specified period after recovery.
Communication is stopped and this diagnostic code is issued.
FAILURE DATA
When the transmitting ECU detects failure of a sensor directly connected to it, this is
the pertinent data used to inform the ECU.
DATA LENGTH ERROR
When the number of data bytes received is different from the prescribed number of bytes,
this diagnosis code is issued.
DYNAMIC RANGE ERROR
When the data received is more or less than the prescribed range, this diagnosis code
is issued.