Inspection Procedure 8: ABS-ECU power supply circuit system



caution
  • When the ABS-ECU power supply voltage becomes 9.7 ± 0.3 V or less, the ABS warning lamp illuminate, and the ABS control is prohibited.
  • If the battery terminal is not tightened properly, a dump surge may occur and the power supply voltage may become abnormally high for a short time.

OPERATION



  • ABS-ECU contains the power supply circuit (+BV terminal) 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 (+BM terminal) 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 (IG1 terminal) 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 through multi-purpose fuse.
  • When malfunction occurs in ABS-ECU power supply, the communication with M.U.T.-III becomes unavailable.

PROBABLE CAUSES



  • Damaged wiring harness and connectors
  • Malfunction of fuse and fusible link
  • Improper tightening of battery terminal
  • Improper tightening of earth bolt
  • Battery failure
  • Charging system failed
  • Malfunction of ABS-ECU

DIAGNOSTIC PROCEDURE


STEP 1. Battery check


Refer to GROUP 54A - Battery Test .

Q. Is the battery in good condition?

Go to Step 3.
Charge or replace the battery. Then go to Step 2.

STEP 2. Charging system check


Refer to GROUP 16 - On-vehicle Service/Alternator Output Line Voltage Drop Test .

Q. Is the charging system in good condition?

Go to Step 3.
Repair or replace the charging system component(s).

STEP 3. M.U.T.-III other system diagnosis code


Check if diagnosis code is set to the ETACS-ECU.

Q. Is the diagnosis code set?

Troubleshoot the ETACS. Refer to GROUP 54A - ETACS .
Go to Step 4.

STEP 4. Voltage measurement at the ABS-ECU connector


(1)Disconnect the connector, and measure at the wiring harness side.
(2)Measure the voltage between ABS-ECU (+BV terminal) and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

Go to Step 6.
Go to Step 5.

STEP 5. Check of short to power supply, short to earth, and open circuit in +BV line between fusible link and ABS-ECU connector


Q. Is the check result normal?

Intermittent malfunction is suspected (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the fusible link, connector(s) or wiring harness. Then go to Step 13.

STEP 6. Voltage measurement at the ABS-ECU connector


(1)Disconnect the connector, and measure at the wiring harness side.
(2)Measure the voltage between ABS-ECU (+BM terminal) and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

Go to Step 8.
Go to Step 7.

STEP 7. Check of short to power supply, short to earth, and open circuit in +BM line between fusible link and ABS-ECU connector


Q. Is the check result normal?

Intermittent malfunction is suspected (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the fusible link, connector(s) or wiring harness. Then go to Step 13.

STEP 8. Voltage measurement at the ABS-ECU connector.


(1)Disconnect the connector, and measure at the wiring harness side.
(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between ABS-ECU (IG1 terminal) and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

Go to Step 10.
Go to Step 9.

STEP 9. Check of short to power supply, short to earth, and open circuit in IG1 line between ETACS-ECU and ABS-ECU connector


Q. Is the check result normal?

Intermittent malfunction is suspected (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the connector(s) or wiring harness. Then go to Step 13.

STEP 10. Resistance measurement at ABS-ECU connector


(1)Disconnect the connector, and measure at the wiring harness side.
(2)Resistance between the ABS-ECU (GND1 terminal) and the body earth, and between the ABS-ECU (GND2 terminal) and the body earth
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 12.
Go to Step 11.

STEP 11. Check of open circuit in GND1, GND2 line between ABS-ECU connector and body earth


Q. Is the check result normal?

Intermittent malfunction is suspected (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the connector(s) or wiring harness. Then go to Step 13.

STEP 12. Retest the system.


Q. Is the communication with M.U.T.-III possible?

Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions ).
Replace the hydraulic unit (integrated with ABS-ECU) (Refer to ). Then go to Step 13.

STEP 13. Retest the system.


Q. Is the communication with M.U.T.-III possible?

Return to Step 1.
This diagnosis is complete.