Precautions on Fault Diagnosis

PRECAUTIONS ON FAULT DIAGNOSIS

REPLACEMENT OF CONTROL UNIT
The control unit itself rarely fails. In most cases, the harnesses have failed (e.g. short-circuit) to cause secondary troubles. Other cases include that the cause has been unknown due to intermittent occurrence of troubles and the troubles are removed accidentally along with replacement of control unit, resulting in misjudgment of cause. Therefore, before replacing the control unit, check the connector joints and whether the unspecified current flows in the control unit due to short-circuit between harnesses.

TROUBLE INTERMITTENTLY OBSERVED
Troubles intermittently observed are mostly attributable to temporary imperfect connection of harnesses and connectors.
When such troubles are found, check the associated circuit according to the following procedure.
1. Check whether improper connectors are plugged in or connector terminals are completely engaged.
2. Check whether the terminals are deformed or damaged. If yes, remove the deformation or damage and connect the terminals securely.
3. It is likely that wires in the harness are falsely broken. Therefore, in examination of failed harness circuit, shake the harness for check to such extent that the harness will not be damaged.

TEST RUN OF FILED TOD VEHICLE
If the TOD indicator lamps experienced faulty operation even once in the past, the failed portion can be identified by use of the procedure "Fault Diagnosis from Trouble Codes" or "Fault Diagnosis from Lighting Status of TOD Indicator Lamps". If the troubles that are only recognized as abnormal phenomena of the vehicle by the driver are observed, conduct the test run in the following procedure to reproduce the faulty phenomena and diagnose the fault for each phenomenon.
1. Start the engine, and check that the TOD indicator lamps are turned on for about two seconds for initial check; the CHECK lamp goes off; and the TOD indicator lamps display the specified drive mode. (if the CHECK lamp starts blinking, read the trouble codes and identify the failed portion.)
2. While keeping the vehicle standstill, operate the 4WD switch and shift the transfer lever to change the modes: 2H mode-->TOD mode-->4L mode-->TOD mode --->2H mode. Check that the TOD indicator lamps correctly display the status whenever the mode is changed. If the transition status is displayed during the shift operation, run the vehicle a little to complete shifting.
3. Slowly start the vehicle in the TOD mode, and add the power to accelerate to at least 40 km/h and maintain the speed for about two minutes. Apply the brake to completely stop the vehicle. Repeat this test pattern at least three times.
4. Turn the steering to the right end (or left end) in the TOD mode, and slowly start the vehicle and make a circle five times. Next, conduct the same test in the 2H mode.
5. Slowly start the vehicle in the TOD mode, and accelerate to at least 40 km/h. Keep the established speed, carefully change the mode in the sequence: "TOD mode-->2H mode -->TOD mode" while checking that the shift is complete in each mode change. After the test, apply the brake to completely stop the vehicle.
6. Slowly start the vehicle in the TOD mode, and accelerate to at least 40 km/h. Apply the brake strongly so that the ABS works, and completely stop the vehicle.
7. Slowly start the vehicle in the 4L mode, and accelerate to at least 20 km/h. Apply the brake to completely stop the vehicle.
If the CHECK lamp starts blinking during the test run, read the trouble codes and give appropriate maintenance according to the fault diagnostic procedure. If the TOD indicator lamps are lit abnormally during the run, check the lighting condition and give appropriate maintenance according to the fault diagnostic procedure. Even if the phenomena are not observed, try to reproduce the abnormal state reported by the customer to the possible extent.

POST-REPAIR CHECK
As long as the starter is not turned off, the TOD indicator lamps continue blinking even after the failed control unit is repaired. Therefore, upon completion of repair, be sure to turn off the starter switch once and then turn on it to conduct the test run sequence specified in steps 1 through 6 above and check that the TOD indicator lamps no longer show any faulty status.