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.