4WD-ECU performs the following checks at a timing shown in the chart below. 4WD-ECU determines
the malfunction occurred when the failure detection conditions are met, and it sets the diagnosis
code and executes the countermeasures for trouble. When the failure resume conditions are met,
ECU determines the status is normal, and resumes the system. Start-up (Initial check just after the ignition switch
is turned ON.)
CPU check
Performs the ROM and RAM check.
Actuator check
After CPU check has been completed, check the driving voltage with the actuator
relay OFF.
Always (During ignition ON status other than initial check
operation)
CPU check
Performs CAN communication and interactive check between CPUs.
Power supply check
Monitors the CPU supply voltage and checks if the voltage is within specifications.
Actuator check
Checks if the actuator relay turns ON according to the control.
Compares the command current value from CPU with the monitored current and checks
if they agree.
External wire connection check
Checks if the input and output of each external wire connection is open,
shorted, or stuck.
