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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 light, 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 DTC 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 energized by the motor switch, which is incorporated in ASC-ECU.
  • When malfunction occurs in ASC-ECU power supply, the communication with scan tool (M.U.T.-IIISE) becomes unavailable.
 
 
 
PROBABLE CAUSES
  • Damaged wiring harness and connectors
  • Fusible link malfunction
  • Improper tightening of battery terminal
  • Improper tightening of ground bolt
  • Battery failure
  • Charging system failed
  • ASC-ECU malfunction
 
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB991223: Harness Set
  • MB992006: Extra Fine Probe
STEP 1. Battery check.
Refer to GROUP 54A - Battery Test .
Is the battery in good condition?
Go to Step 3.
Replace the battery (Refer to GROUP 54A - Battery ). Then go to Step 2.
 
STEP 2. Charging system check.
Refer to GROUP 16 - On-vehicle Service/Generator Output Line Voltage Drop Test .
Is the charging system in good condition?
Go to Step 3.
Repair or replace the charging system component(s) (Refer to GROUP 16 - Generator ).
 
STEP 3. Using scan tool (M.U.T.-IIISE), check other system DTC.
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect the Scan Tool (M.U.T.-IIISE) ."
(2) Check if DTC is set in the ETACS-ECU.
Is the DTC 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 ground.
OK: Approximately system voltage
Is the check result normal?
Go to Step 6.
Go to Step 5.
 
STEP 5. Check of short to power supply, short to ground, and open circuit in +BV line between fusible link and ASC-ECU connector.
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.
 
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 ground.
OK: Approximately system voltage
Is the check result normal?
Go to Step 8.
Go to Step 7.
 
STEP 7. Check of short to power supply, short to ground, and open circuit in +BM line between fusible link and ASC-ECU connector.
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.
 
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 ground.
OK: Approximately system voltage
Is the check result normal?
Go to Step 10.
Go to Step 9.
 
STEP 9. Check of short to power supply, short to ground, and open circuit in IG1 line between ETACS-ECU and ASC-ECU connector.
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.
 
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 ground, and between the ASC-ECU connector (GND2 terminal) and the body ground
OK: Continuity exists (2 Ω or less)
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 ground.
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.
 
STEP 12. Retest the system.
Is the communication with scan tool (M.U.T.-IIISE) 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 ).