C1078

DIAGNOSTIC TROUBLE CODE PROCEDURES

DTC C1078: Tire with incorrect diameter equipped

CAUTION: If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, always diagnose the CAN bus lines.

OPERATION
If the vehicle is driven with a tire with incorrect diameter (high-pressure type spare tire or flat tire) installed to either wheel in the AWD mode, AWD-ECU controls the coupling in high torque. If this is the case, the coupling temperature may rise to cause a seizure.

^ If the difference in rotation speed between the front and rear wheels exceeds a specific value continuously, the DTC No. C1078 is set, the AWD/LOCK indicators flash alternately, and the mode is switched to the 2WD mode.

DTC SET CONDITIONS
If the following conditions are met, AWD-ECU gradually reduces the AWD control torque to the specified torque, flashes the AWD/LOCK indicators alternately, and sets the DTC No. C1078.

^ AWD selector switch: AWD/LOCK
^ If the vehicle is driven with abnormal tire pressure or tires of different brands.

TROUBLESHOOTING HINTS

Current trouble
^ Tire with incorrect diameter (high-pressure type spare tire or flat tire) equipped
^ Improper adjusted tire pressure

Past trouble
^ Tire with incorrect diameter (high-pressure type spare tire or flat tire) has been installed.
^ The tire pressure has been adjusted due to improper tire pressure.

DIAGNOSIS
^ MB991958: Scan Tool (M.U.T.-III Sub Assembly)
^ MB991824: Vehicle Communication Interface
^ MB991827: M.U.T.-III USB Cable
^ MB991910: M.U.T.-III Main Harness A

STEP 1. Scan tool MB991958 CAN bus diagnostics
Use scan tool MB991958 to diagnose the CAN bus lines.

Q:Is the check result normal?
YES: Go to Step 3.
NO: Repair the CAN bus line. On completion, go to Step 2.

STEP 2. Check whether the DTC is reset after repairing the CAN bus line.
(1) Erase the DTC.
(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 20 seconds or longer.
(3) Check if the DTC is set.

Q:Is the DTC No. C1078 set?
YES: Go to Step 3.
NO: This diagnosis is complete.

STEP 3. Tire check

Q:Are all installed wheels and tires same in size?
YES: Go to Step 4.
NO: Install the same size wheels and tires. Then go to Step 4.

STEP 4. Tire pressure check
Check that the tire pressure of the installed tires agrees with the tire pressure specified on the tire pressure label.

Q:Is the tire pressure normal?
YES: Go to Step 6.
NO: Adjust the tire pressure. Then go to Step 5.

STEP 5. Check whether the DTC 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 20 seconds or longer.

Q:Is the DTC No. C1078 set?
YES: Go to Step 6.
NO: This code is set because the tire pressure was improper or a tire with incorrect diameter is installed.

STEP 6. Scan tool MB991958 data list
Check the following service data.

^ 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?
YES: Go to Step 7.
NO: Troubleshoot the ABS system. Then go to Step 7.

STEP 7. Check whether the DTC 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 20 seconds or longer.

Q:Is the DTC No. C1078 set?
YES: Replace AWD-ECU. Then go to Step 8.
NO: This diagnosis is complete.

STEP 8. Check whether the DTC is reset.

Q:Is the DTC No. C1078 set?
YES: Diagnose again from Step 1.
NO: This diagnosis is complete.