Inspection Procedure 8: ABS-ECU Power Supply Circuit System

Inspection Procedure 8: ABS-ECU Power Supply Circuit System








SYSTEM OPERATION
^ The ABS-ECU power supply signal energized by the ignition switch (IG1) is transmitted to ABS-ECU (terminal No.7) via multipurpose fuse No. 12.
^ The ABS-ECU power supply and the valve power supply are transmitted to ABS-ECU (terminal No.26) via fusible link No. 27.
^ When malfunction occurs in ABS-ECU power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES
^ Damaged wiring harness and connectors
^ Blown fuse
^ Battery failure
^ Charging system failed
^ ABS-ECU malfunction

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
^ MB991974: ABS check harness

STEP 1. Voltage measurement at the A-03 ABS-ECU connector
1) Disconnect the connector, connect special tool MB991974 to the harness-side connector, and measure the voltage at the special tool connector side.

NOTE: Do not connect the special tool MB991974 to ABS-ECU.

2) Turn the ignition switch to the ON position.





3) Measure the voltage between terminal No.7 and body ground.
OK: Approximately battery voltage

Q: Is the check result normal?
YES: Go to Step 2.
NO: Go to Step 8.

STEP 2. Voltage measurement at the A-03 ABS-ECU connector
1) Disconnect the connector, connect special tool MB991974 to the harness-side connector, and measure the voltage at the special tool connector side.

NOTE: Do not connect the special tool MB991974 to ABS-ECU.

2) Turn the ignition switch to the ON position.





3) Measure the voltage between terminal No.26 and body ground.
OK: Approximately battery voltage

Q: Is the check result normal?
YES: Go to Step 5.
NO: Go to Step 3.

STEP 3. Check the fusible link No.27
Q: Is the check result normal?
YES: Go to Step 4.
NO: Replace the fusible link No.27.

STEP 4. Connector check: A-03 ABS-ECU connector
Q: Is the check result normal?
YES: Repair the wiring harness between fusible link No.27 and the A03 ABS-ECU connector terminal No.32.
NO: Repair the defective connector.

STEP 5. Voltage measurement at the A-03 ABS-ECU connector
1) Disconnect the connector, connect special tool MB991974 to the harness-side connector, and measure the voltage at the special tool connector side.

NOTE: Do not connect the special tool MB991974 to ABS-ECU.

2) Turn the ignition switch to the ON position.





3) Voltage between terminal No. 13 and body ground
OK: Approximately battery voltage

Q: Is the check result normal?
YES: Go to Step 9.
NO: Go to Step 6.

STEP 6. Check the fusible link No.26
Q: Is the check result normal?
YES: Go to Step 7.
NO: Replace the fusible link No.26.

STEP 7. Connector check: A-03 ABS-ECU connector
Q: Is the check result normal?
YES: Repair the wiring harness between fusible link No.26 and the A03 ABS-ECU connector terminal No. 13.
NO: Repair the defective connector.

STEP 8. Check the fuse No.12 and No.14 and fusible link No.34
Q: Is the check result normal?
YES: Go to Step 9.
NO: Replace the abnormal fuse or fusible link.

STEP 9. Wiring harness check between the A-03 ABS-ECU connector terminal No.1 and body ground, and between the A-03 ABS-ECU connector terminal No.14 and body ground
^ Check the ground wires for open circuit.

Q: Is the check result normal?
YES: Go to Step 10.
NO: Repair the wiring harness.

STEP 10. Battery check
Refer to Battery Test.
Q: Is the battery in good condition?
YES: Go to Step 11.
NO: Charge or replace the battery.

STEP 11. Charging system check
Refer to Output Current Test.
Q: Is the charging system in good condition?
YES: Go to Step 12.
NO: Repair or replace the charging system component(s).

STEP 12. Retest the system.
Q: Is the communication with scan tool possible?
YES: An intermittent malfunction may be present.
NO: Make sure that the scan tool cable is properly connected and the V.C.I. switch is ON, and then replace ABS-ECU.