FUNCTION
The main functions of 4WD-ECU are as follows:
1. Communication function
- CAN communication with other ECUs (Engine ECU, CVT-ECU, A/T-ECU, ABS/ASC-ECU, steering wheel sensor, ETACS)
- Communication with drive mode switch: The signal from the drive mode switch changes the drive mode.
- Combination meter display: Drive mode is displayed.
2. Coupling control function
Current output: Differential control function of the electronic control coupling according to the vehicle conditions
3. ECU self-diagnosis function
- Initial check: ROM check, relay check, etc.
- Recording function of diagnosis codes and freeze frame data in case of failure
- System shutdown function after failure detection, "4WD-E" and "LOCK" indicator warning <standard meter> and message indication on display <high contrast meter>
- Normal control: Malfunction of CPU power supply, relay check, open or short circuit of the I/O signal, abnormal CAN communication
FAIL-SAFE FUNCTION
FAILURE DETECTION
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.
note For the fail-safe specification, refer to Workshop Manual.
1. 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.
2. 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.
DIAGNOSTIC FUNCTION
4WD-ECU has the following functions for easier system checks. All of the following items can be diagnosed using the M.U.T.-III.
Diagnosis code set
Service data output
Actuator test
Freeze frame data output