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Inspection Procedure 8: ABS-ECU Power Supply Circuit System
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- ABS-ECU contains the power supply circuit (terminal No. 26) for the solenoid valve. The solenoid valve is energised by the valve relay, which is incorporated in ABS-ECU.
- ABS-ECU contains the power supply circuit (terminal No.13) for the pump motor. The pump motor is energised by the motor relay, which is incorporated in ABS-ECU.
- ABS-ECU contains the power supply circuit (terminal No.7) for ABS-ECU. When the ignition switch (IG1) is turned ON, the voltage is applied to the relay incorporated in ETACS-ECU to turn ON the relay, and the power is supplied from fusible link No.34 through multi-purpose fuse No.12.
- When malfunction occurs in ABS-ECU power supply, the communication with scan tool becomes unavailable.
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- Damaged wiring harness and connectors
- Malfunction of fuse and fusible link
- Improper tightening of battery terminal
- Improper tightening of ground bolt
- Battery failure
- Charging system failed
- Malfunction of ABS-ECU
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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
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Refer to GROUP 54A - Battery Test  .
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Q.
Is the battery in good condition?
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 Go to Step 3.
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 Charge or replace the battery. Then go to Step 2.
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STEP 2. Charging system check
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Refer to GROUP 16 - Charging System .
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Q.
Is the charging system in good condition?
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Go to Step 3.
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Repair or replace the charging system component(s).
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STEP 3. Connector check: A-03 ABS-ECU connector
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Q.
Is the check result normal?
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Go to Step 4.
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NO : Repair the damaged connector.
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STEP 4. Fusible link check: Check the fusible link No.27.
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Q.
Is the check result normal?
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Go to Step 6.
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Go to Step 5.
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STEP 5. Resistance measurement at A-03 ABS-ECU connector
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(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
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Do not connect the special tool to ABS-ECU.
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(2)Removal the fusible link No.27.
(3)Resistance between the terminal No.26 and the body ground.
OK: No continuity
Q.
Is the check result normal?
Replace the fusible link No.27. Then go to Step 22.
The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.26 and the fusible link No.27, and then replace the fusible link No.27. Then go to Step 22.
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STEP 6. Check the fuse No.12.
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Visually check for open circuit in fuse No.12.
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Q.
Is the check result normal?
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Go to Step 9.
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Go to Step 7.
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STEP 7. Connector check: C-128 intermediate connector, C-317 ETACS-ECU connector
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Q.
Is the check result normal?
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Go to Step 8.
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NO : Repair the damaged connector.
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STEP 8. Resistance measurement at A-03 ABS-ECU connector
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(1)Disconnect the C-317 ETACS-ECU connector.
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(2)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
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Do not connect the special tool to ABS-ECU.
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(3)Resistance between the terminal No.7 and the body ground.
OK: No continuity
Q.
Is the check result normal?
Replace the fuse No.12. Then go to Step 22.
The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.7 and the C-317 ETACS-ECU connector terminal No.5, and then replace the fuse No.12. Then go to Step 22.
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STEP 9. Fusible link check: Check the fusible link No.34.
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Q.
Is the check result normal?
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Go to Step 12.
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Go to Step 10.
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STEP 10. Connector check: C-309 ETACS-ECU connector
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Q.
Is the check result normal?
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Go to Step 11.
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NO : Repair the damaged connector.
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STEP 11. Resistance measurement at C-309 ETACS-ECU connector
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(1)Removal the fusible link No.34.
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(2)Disconnect the C-309 ETACS-ECU connector, and then measure the resistance at the connector side.
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(3)Resistance between the terminal No.1 and the body ground.
OK: No continuity
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Q.
Is the check result normal?
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Replace the fusible link No.34. Then go to Step 22.
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The short circuit may be present in the power supply circuit. Repair the wiring harness between the C-309 ETACS-ECU connector terminal No.1 and the fusible link No.34, and then replace the fusible link No.34. Then go to Step 22.
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STEP 12. Voltage measurement at the A-03 ABS-ECU connector
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(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the voltage at the special tool connector side.
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Do not connect the special tool to ABS-ECU.
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(2)Measure the voltage between terminal No.26 and body ground.
OK: Battery positive voltage
Q.
Is the check result normal?
Go to Step 13.
The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.26 and the fusible link No.27. Then go to Step 22.
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STEP 13. Measure the voltage at the C-309 ETACS-ECU connector.
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(1)Disconnect the connector, and measure at the wiring harness-side connector.
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(2)Measure the voltage between the terminal No.1 and the body ground.
OK: Battery positive voltage
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Q.
Is the check result normal?
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Go to Step 14.
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The open circuit may be present in the power supply circuit. Repair the wiring harness between the C-309 ETACS-ECU connector terminal No.1 and fusible link No.34. Then go to Step 22.
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STEP 14. Connector check: C-317 ETACS-ECU connector
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Q.
Is the check result normal?
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Go to Step 15.
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NO : Repair the damaged connector.
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STEP 15. Measure the voltage at the C-317 ETACS-ECU connector.
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(1)Measure by backprobing without disconnecting the connector.
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(2)Turn the ignition switch to the ON position.
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(3)Measure the voltage between the terminal No.6 and the body ground.
OK: Battery positive voltage
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Q.
Is the check result normal?
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Go to Step 17.
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Go to Step 16.
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STEP 16. Connector check: C-212 ignition switch connector
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Q.
Is the check result normal?
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Repair the wiring harness between C-212 ignition switch connector terminal No.2 and C-317 ETACS-ECU connector terminal No.6. Then go to Step 22.
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NO : Repair the damaged connector.
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STEP 17. Measure the voltage at the C-317 ETACS-ECU connector.
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(1)Measure at ETACS-ECU side connector.
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Do not disconnect the connector.
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(2)Turn the ignition switch to the ON position.
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(3)Measure the voltage between terminal No.5 and the body ground by backprobing.
OK: Battery positive voltage
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Q.
Is the check result normal?
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Go to Step 18.
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Replace the ETACS-ECU (Refer to GROUP 54A - ETACS-ECU .) Then go to Step 22.
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STEP 18. Connector check: C-128 intermediate connector
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Q.
Is the check result normal?
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Go to Step 19.
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NO : Repair the damaged connector.
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STEP 19. Voltage measurement at A-03 ABS-ECU connector
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(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
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Do not connect the special tool to ABS-ECU.
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(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between terminal No.7 and body ground.
OK: Battery positive voltage
Q.
Is the check result normal?
Go to Step 20.
The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.7 and the C-317 ETACS-ECU connector terminal No.5. Then go to Step 22.
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STEP 20. Resistance measurement at A-03 ABS-ECU connector
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(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
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Do not connect the special tool to ABS-ECU.
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(2)Resistance between the terminal No.1 and the body ground, and between the terminal No.14 and the body ground
OK: Continuity exists (2 Ω or less)
Q.
Is the check result normal?
Go to Step 21.
An open circuit may be present in the ground circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.1 and the body ground, and between the A-03 ABS-ECU connector terminal No.14 and the body ground. Then go to Step 22.
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STEP 21. Retest the system.
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Q.
Is the communication with scan tool possible?
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Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction .)
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Make sure that the M.U.T.-III cable is properly connected and the V.C.I. switch is ON, and then replace the ABS-ECU (Refer to ). Then go to Step 22.
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STEP 22. Retest the system.
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Q.
Is the communication with scan tool possible?
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Return to Step 1.
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The procedure is complete.
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