If the EPS-ECU sets the diagnosis
code No. C1521, diagnose the CAN bus lines. If there is any fault in the CAN bus lines, an incorrect diagnosis
code may be set.
Before replacing ECU, ensure that the communication circuit is normal.
DIAGNOSIS CODE SET CONDITIONS
The diagnosis code No. C1521 is set when the system receives an abnormal vehicle speed
signal, and the microprocessor determines that the vehicle speed measurement system is faulty.
CRITERIA FOR JUDGING MALFUNCTION
An abnormality is judged if the vehicle speed signal is not sent to EPS-ECU after the
electric motor switch is turned from LOOK (OFF) to ON position.
PROBABLE CAUSES
Defective wiring harness or connector between the ASC-ECU and the wheel speed
sensor
Malfunction of the wheel speed sensor or vehicle speed detection encoder
Malfunction of the power supply to ASC-ECU
Malfunction of the ASC-ECU.
Malfunction of the EPS-ECU
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III CAN bus diagnosis
Use the M.U.T.-III to diagnose the CAN bus lines.
Q.
Is the check result normal?
Go to Step 2.
Repair the CAN bus lines. (Refer to GROUP 54C, Troubleshooting .
) After repairing the CAN bus lines, go to STEP 2.
STEP 2. Use M.U.T.-III to confirm a diagnosis code of other systems.
Check that the ASC-ECU sets a diagnosis code.
Q.
Is the diagnosis code set?
Perform the troubleshooting for the ASC. Refer to .
Go to Step 3.
STEP 3. Diagnosis code recheck
Recheck if the diagnosis code is set.
(1)Turn the electric motor switch to the "LOCK" (OFF) → "ON" position.
(2)Check if the diagnosis code No. C1521 is set as a current trouble.
Q.
Is diagnosis code C1521 set?
Replace the EPS-ECU, and then go to Step 4 .
Intermittent malfunction. (Refer to GROUP 00 - How to Cope with Intermittent
Malfunction .)
STEP 4. Diagnosis code recheck
Recheck if the diagnosis code is set.
(1)Turn the electric motor switch to the "LOCK" (OFF) → "ON" position.
(2)Check if the diagnosis code No. C1521 is set.
Q.
Is diagnosis code C1521 set?
Replace the hydraulic unit (ASC-ECU). (Refer to GROUP 35C - Hydraulic
Unit .)
Go to Step 2.
Repair the CAN bus lines. (Refer to GROUP 54C, Troubleshooting 
.
) After repairing the CAN bus lines, go to STEP 2.