Inspection Procedure 2: Power Supply Circuit System
INSPECTION PROCEDURE 2: Power Supply Circuit System
CIRCUIT OPERATION
^ The ABS-ECU is energized by the ignition switch (IG1) through multi-purpose fuse 23 and the ABS-ECU terminal 20.
^ If the power supply to the ABS-ECU has failed, the scan tool (M.U.T.-III Sub Assembly) will not be able to communicate with it.
TROUBLESHOOTING HINTS (The most likely causes for this case:)
^ Damaged wiring harness or connector
^ Defective battery
^ Charging system failed
^ Malfunction of the hydraulic unit (integrated with ABS-ECU)
DIAGNOSIS
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
^ MB991970: ABS Check Harness
STEP 1. Measure the voltage at ABS-ECU connector A-02.
1) Disconnect the connector A-02, and connect special tool ABS Check Harness (MB991970) to the wiring harness-side connector.
NOTE: Do not connect special tool ABS Check Harness (MB991970) to the ABS-ECU.
2) Turn the ignition switch to the "ON" position.
3) Measure the voltage between terminal 20 and ground. It should measure approximately 12 volts (battery positive voltage).
Q: Is battery positive voltage (approximately 12 volts) present?
YES: Go to Step 3.
NO: Go to Step 2.
STEP 2. Check ABS-ECU connector A-02, junction block connectors C-214, C-215 and ignition switch connector C-308 for loose, corroded or damaged terminals, or terminals pushed back in the connector.
^ ABS-ECU connector A-02
^ Junction block connectors C-214 and C-215
^ Ignition switch connector C-308
Q: Are the connectors and terminals in good condition?
YES: An open or short circuit may be present in the power supply line to the ABS-ECU. Repair the wiring harness between ABS-ECU connector A02 terminal 20 and ignition switch connector C-308 terminal
2. Then go to Step 8.
NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. Then go to Step 8.
STEP 3. Measure the resistance at ABS-ECU connector A-02.
1) Disconnect the connector A-02, and connect special tool ABS Check Harness (MB991970) to the wiring harness-side connector.
NOTE: Do not connect special tool ABS Check Harness (MB991970) to the ABS-ECU.
2) Measure the resistance between terminal 2, 18 and ground. It should be 2 ohms or less.
Q: Is the measured resistance 2 ohms or less?
YES: Go to Step 5.
NO: Go to Step 4.
STEP 4. Check ABS-ECU connector A-02 for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Q: Is ABS-ECU connector A-02 damaged?
YES: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. Then go to Step 8.
NO: An open circuit may be present in the ground circuit. Repair the wiring harness between ABS-ECU connector A-02 terminals 2, 18 and the body ground. Then go to Step 8.
STEP 5. Check the battery.
Check the battery.
Q: Is the battery in good condition?
YES: Go to Step 6.
NO: Charge or replace the battery. Then go to Step 8.
STEP 6. Check the charging system.
Check the charging system.
Q: Is the charging system in good condition?
YES: Go to Step 7.
NO: Repair or replace the charging system component(s). Then go to Step 8.
STEP 7. Retest the system.
Q: Can the ABS-ECU communicate with the scan tool (M.U.T.-III Sub Assembly)?
YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points How to Cope with Intermittent Malfunction.
NO: Replace the ABS-ECU. Then go to Step 8.
STEP 8. Retest the system.
Q: Can the ABS-ECU communicate with the scan tool (M.U.T.-III Sub Assembly)?
YES: The procedure is complete.
NO: Go to Step 1.