Inspection Procedure
12: ASC-ECU power supply circuit system.
caution
When the ASC-ECU
power supply voltage becomes 9.7 ± 0.3 V or less, the ABS warning lamp, ASC warning display,
and ASC OFF display illuminate, and the ABS, stability control, and TCL controls are 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.
If there is any problem in the CAN bus lines, an incorrect diagnosis code may be
set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - CAN
Bus Diagnostics Table ).
Whenever ECU is replaced, ensure that the CAN bus lines are normal.
OPERATION
ASC-ECU contains the power supply circuit (+BV
terminal) for the solenoid valve. The solenoid valve is energized by the valve relay, which
is incorporated in ASC-ECU.
ASC-ECU contains the power supply circuit (IG1 terminal) for ASC-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 the fusible link.
ASC-ECU contains the power supply circuit (+BM terminal) for the pump motor.
The pump motor is energised by the motor switch, which is incorporated in ASC-ECU.
When malfunction occurs in ASC-ECU power supply, the communication with M.U.T.-III
becomes unavailable.
PROBABLE CAUSES
Damaged wiring harness and connectors
Fusible link malfunction
Improper tightening of battery terminal
Improper tightening of earth bolt
Battery failure
Charging system failed
ASC-ECU malfunction
DIAGNOSIS 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 ASC-ECU connector
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Measure the voltage between ASC-ECU connector (+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 ASC-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 ASC-ECU connector
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Measure the voltage between ASC-ECU connector (+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 ASC-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 ASC-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 ASC-ECU connector (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 ASC-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 ASC-ECU connector
(1)Disconnect the connector, and measure at the wiring harness side.
(2)Resistance between the ASC-ECU connector (GND1 terminal) and the body earth, and
between the ASC-ECU connector (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 ASC-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 ASC-ECU) (Refer to ).
Then go to Step 13.
.
Go to Step 3
Charge or replace the battery. Then go to Step 2.