Code No. C1078: Tyre with incorrect diameter equipped
caution
If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, always diagnose the CAN bus lines.
OPERATION
If the vehicle is driven with a tyre with incorrect diameter (high-pressure type spare tyre or flat tyre) installed to either wheel in the 4WD mode, 4WD-ECU controls the coupling in high torque. If this is the case, the coupling temperature may rise to cause a seizure.
DIAGNOSIS CODE SET CONDITIONS
If the following conditions are met, 4WD-ECU gradually reduces the 4WD control torque to the specified torque, flashes the 4WD/LOCK indicators alternately, and sets the diagnosis code No. C1078.
4WD selector switch: 4WD/LOCK
If the vehicle is driven with abnormal tyre pressure or tyres of different brands, diagnosis code No. C1078 is set and the mode is switched to the 4WD AUTO mode.
If the difference in rotation speed between the front and rear wheels exceeds a specific value continuously, the diagnosis code No. C1078 is set, the 4WD/LOCK indicators flash alternately, and the mode is switched to the 2WD mode.
PROBABLE CAUSES
Current trouble
Tyre with incorrect diameter (high-pressure type spare tyre or flat tyre) equipped
Improper adjusted tyre pressure
Past trouble
Tyre with incorrect diameter (high-pressure type spare tyre or flat tyre) has been installed.
The tyre pressure has been adjusted due to improper tyre pressure.
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III CAN bus diagnostics
Use M.U.T.-III to diagnose the CAN bus lines.
Q.
Is the check result normal?
Go to Step 3.
Repair the CAN bus line. (Refer to GROUP 54C - Troubleshooting .) On completion, go to Step 2.
STEP 2. Check whether the diagnosis code is reset after repairing the CAN bus line.
(1)Erase the diagnosis code.
(2)Drive the vehicle straight with throttle opening angle of approximately 50% or less, and constant vehicle speed of 30 km/h or higher for 1 minute or longer.
(3)Check if the diagnosis code is set.
Q.
Is the diagnosis code No. C1078 set?
Go to Step 3.
This diagnosis is complete.
STEP 3. Tyre check
Q.
Are all installed wheels and tyres same in size?
Go to Step 4.
Install the same size wheels and tyres. Then go to Step 4.
STEP 4. Tyre pressure check
Check that the tyre pressure of the installed tyres agrees with the tyre pressure specified on the tyre pressure label.
Q.
Is the tyre pressure normal?
Go to Step 5.
Adjust the tyre pressure. Then go to Step 5.
STEP 5. Check whether the diagnosis code is reset.
Drive the vehicle straight with throttle opening angle of approximately 50% or less, and constant vehicle speed of 30 km/h or higher for 1 minute or longer.
Q.
Is the diagnosis code No. C1078 set?
Go to Step 6.
This code is set because the tyre pressure was improper or a tyre with incorrect diameter is installed.
STEP 6. M.U.T.-III data list
Check the following service data. (Refer to .)
Item 16: FL wheel speed sensor
Item 17: FR wheel speed sensor
Item 18: RL wheel speed sensor
Item 19: RR wheel speed sensor
Q.
Is the check result normal?
The trouble can be an intermittent malfunction. (Refer to GROUP 00 - How to Cope with Intermittent Malfunction .)
Troubleshoot the ABS system. (Refer to GROUP 35C - Troubleshooting .) Then go to Step 7.
STEP 7. Check whether the diagnosis code is reset.
Drive the vehicle straight with throttle opening angle of approximately 50% or less, and constant vehicle speed of 30 km/h or higher for 1 minute or longer.
Q.
Is the diagnosis code No. C1078 set?
Replace 4WD-ECU. (Refer to .) Then go to Step 8.
This diagnosis is complete.
STEP 8. Check whether the diagnosis code is reset.
Go to Step 3.
Repair the CAN bus line. (Refer to GROUP 54C - Troubleshooting 
.) On completion, go to Step 2.