Inspection Procedure 1

Inspection Procedure 1: Cannot communicate with KOS-ECU using the scan tool.

CAUTION:
Before replacing the ECU, ensure that the communication circuit is normal.

TECHNICAL DESCRIPTION (COMMENT)

If the M.U.T.-III cannot communicate with the KOS-ECU, the CAN bus lines may be defective.
If the KOS-ECU does not work, the KOS-ECU or the power supply circuit may be defective.

TROUBLESHOOTING HINTS

- Malfunction of the power supply or ground of KOS-ECU
- Malfunction of CAN bus line

DIAGNOSIS

STEP 1. Using scan tool MB991958, diagnose the CAN bus line.

(1)
CAUTION:
To prevent damage to scan tool MB991958, always turn the power supply mode of the engine switch to the OFF position before connecting or disconnecting scan tool MB991958.

Connect scan tool MB991958. Refer to "How to connect scan too (M.U.T.-III) Reading and Clearing Diagnostic Trouble Codes."

(2)Turn the power supply mode of the engine switch to ON.

(3)Diagnose the CAN bus line.

(4)Turn the power supply mode of the engine switch to OFF.

Q. Is the CAN bus line found to be normal?

YES Go to Step 2.
NO Repair the CAN bus line CAN Bus Diagnostics Chart).
STEP 2. Check the power supply circuit and the ground circuit to KOS-ECU.

Refer to Inspection Procedure 3 "Abnormality in KOS-ECU power supply and ground circuits" Inspection Procedure 3.

Q. Is the power supply circuit and the ground circuit to KOS-ECU in good condition ?

YES Go to Step 3.
NO Repair the power supply circuit and the ground circuit to KOS-ECU.
STEP 3. Retest the system

Check if scan tool can communicate with KOS-ECU.

Q. Does the scan tool cannot with KOS-ECU?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace KOS-ECU and register the ID codes (Refer to ID Codes Registration Procedure).