Inspection Procedure 3

INSPECTION PROCEDURE 3: TCL/ASC-ECU power supply circuit system





















CIRCUIT OPERATION

- The TCL/ASC-ECU is energized by the ignition switch (IG1) through multi-purpose fuse No.2 and the TCL/ASC-ECU terminal 4.
- If the power supply to the TCL/ASC-ECU has failed, scan tool MB991958 will not be able to communicate with it.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CASE:)

- Damaged wiring harness or connector
- Defective battery
- Charging system failed
- Malfunction of the hydraulic unit (integrated with TCL/ASC-ECU)

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A
- MB991997: ASC Check Harness

STEP 1. Measure the voltage at TCL/ASC-ECU connector A-38.





(1)Disconnect the connector A-38, and connect special tool MB991997 to the wiring harness-side connector.
NOTE:
Do not connect special tool MB991997 to the TCL/ASC-ECU.

(2)Turn the ignition switch to the "ON" position.
(3)Measure the voltage between terminal 4 and ground. It should measure approximately 12 volts (battery positive voltage).

Q. Is battery positive voltage (approximately 12 volts) present?

YES Go to Step 3.

NO Go to Step 2.

STEP 2. Check the following connectors.

















- TCL/ASC-ECU connector A-38
- Junction block connectors C-202 and C-203
- Intermediate connector C-24
- Ignition switch connector C-308
Check the connectors, for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Are the connectors and terminals in good condition?

YES An open or short circuit may be present in the power supply line to the TCL/ASC-ECU. Repair the wiring harness between TCL/ASC-ECU connector A-38 terminal 4 and ignition switch connector C-308 terminal 4. Go to Step 8.

NO Repair or replace the damaged component(s). Harness Connector Inspection. Then go to Step 8.

STEP 3. Measure the resistance at TCL/ASC-ECU connector A-38.





(1)Disconnect the connector A-38, and connect special tool MB991997 to the wiring harness-side connector.
NOTE:
Do not connect special tool MB991997 to the TCL/ASC-ECU.

(2)Measure the resistance between terminal 16, 47 and ground. It should be 2 ohms or less.

Q. Is the measured resistance 2 ohms or less?

YES Go to Step 5.

NO Go to Step 4.

STEP 4. Check TCL/ASC-ECU connector A-38 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Are the connectors and terminals in good condition?

YES An open circuit may be present in the ground circuit. Repair the wiring harness between TCL/ASC-ECU connector A-38 terminals 16, 47 and the body ground. Then go to Step 8.

NO Repair or replace the damaged component(s). Harness Connector Inspection. Then go to Step 8.

STEP 5. Check the battery.

Check the battery Battery Test).

Q. Is the battery in good condition?

YES Go to Step 6.
NO Charge or replace the battery. Then go to Step 8.
STEP 6. Check the charging system.

Check the charging system Initial Inspection and Diagnostic Overview).

Q. Is the charging system in good condition?

YES Go to Step 7.
NO Repair or replace the charging system component(s).Then go to Step 8.
STEP 7. Retest the system.

Q. Can the TCL/ASC-ECU communicate with the scan tool (M.U.T.-III Sub Assembly)?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.
NO Replace the TCL/ASC-ECU. Then go to Step 8.
STEP 8. Retest the system.

Q. Can the TCL/ASC-ECU communicate with the scan tool (M.U.T.-III Sub Assembly)?

YES The procedure is complete.
NO Go to Step 1.