Inspection Procedure 3: TCL/ASC-ECU Power Supply Circuit System

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 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). Then go to Step 8.

STEP 3. Measure the resistance at TCL/ASC-ECU connector A38.





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). Then go to Step 8.

STEP 5. Check the battery.
Check the battery.
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.
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.
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.