Inspection Procedure A-4
Communication with the front-ECU is impossibleFront-ECU Power Supply And SWS Communication Circuit:
Connectors:
CIRCUIT OPERATION
- The power supply to the front-ECU is provided by the battery and the ignition switch (IG2).
- If the power supply system from the battery is defective, the system operates by the power supply from the ignition switch (IG2).
TECHNICAL DESCRIPTION (COMMENT)
It is suspected that the power supply circuit to the front-ECU is defective, or the wiring harness between the SWS monitor kit and the front-ECU or their connector(s) is damaged. If the battery power supply circuit to the ECU (terminal No. 7 of the front-ECU) is damaged, also check the power supply circuit from the ignition switch (IG2) (terminal No. 30 of the front-ECU), and repair if necessary.
TROUBLESHOOTING HINTS
- Malfunction of the ETACS-ECU
- Malfunction of the front-ECU
- Damaged harness wires or connectors
DIAGNOSIS
Required Special Tools:
- MB991223: Test Harness Set
- MB991502: Scan Tool (MUT-II)
- MB991862: SWS monitor kit
STEP 1. Use scan tool to select "ECU CHECK" on the SWS monitor display.
Check the ETACS-ECU.
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502. Also connect SWS monitor kit MB991862 after turning on scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Connect SWS monitor kit MB991862 to the column switch connector.
3. When the ignition switch is turned to the "LOCK" (OFF) position, scan tool MB991502 should show "OK" on the "ETACS ECU" menu.
Q: Is "OK" displayed on the "ETACS ECU" menu?
YES: Go to STEP 2.
NO: Refer to Inspection Procedure A-3 "Communication with ETACS-ECU is impossible."
STEP 2. Measure at front-ECU connector A-10X in order to check the battery circuit of power supply system to the front-ECU.
1. Disconnect front-ECU connector A-10X, and measure at the relay box side.
2. Measure the voltage between terminal 7 and ground.
- The measured value should be approximately 12 volts (battery positive voltage).
Q: Does the measured voltage correspond with this range?
YES: Go to Step 5.
NO: Go to Step 3.
STEP 3. Check the front-ECU connector A-10X for damage.
Q: Is the front-ECU connector A-10X in good condition?
YES: Go to Step 4.
NO: Repair or replace the connector. Refer to Harness Connector Inspection. The system should communicate with the front-ECU normally.
STEP 4. Check the wiring harness between front-ECU connector A-10X and the battery.
Q: Is the wiring harness between front-ECU connector A-10X and the battery in good condition?
YES: No action to be taken.
NO: Repair the wiring harness. The system should communicate with the front-ECU normally.
STEP 5. Measure at front-ECU connector A-11X in order to check the ground circuit to the front-ECU.
1. Disconnect front-ECU connector A-11X, and measure at the relay box side.
2. Measure the resistance value between terminal 31 and ground.
- The measured value should be 2 Ohm or less.
Q: Does the measured resistance value correspond with this range?
YES: Go to Step 8.
NO: Go to Step 6.
STEP 6. Check the front-ECU connector A-11X for damage.
Q: Is front-ECU connector A-11X in good condition?
YES: Go to Step 7.
NO: Repair or replace the connector. Refer to Harness Connector Inspection. The system should communicate with the front-ECU normally.
STEP 7. Check the wiring harness between front-ECU connector A-11X and the ground.
Q: Is the wiring harness between front-ECU connector A-11X and ground in good condition?
YES: No action to be taken.
NO: Repair the wiring harness. The system should communicate with the front-ECU normally.
STEP 8. Check the front-ECU connector A-11X and ETACS-ECU connector C-228 for damage.
Q: Are front-ECU connector A-11X and ETACS-ECU connector C-228 in good condition?
YES: Go to Step 9.
NO: Repair or replace the connector. Refer to Harness Connector Inspection. The system should communicate with the front-ECU normally.
STEP 9. Check the wiring harness between front-ECU connector A-11X and ETACS-ECU connector C-228.
NOTE: Also check intermediate connector C-129. If intermediate connectors C-129 is damaged, repair or replace the connector as described in Harness Connector Inspection.
Q: Is the wiring harness between front-ECU connector A-11X and ETACS-ECU connector C-228 in good condition?
YES: Go to Step 10.
NO: Repair the wiring harness. The system should communicate with the front-ECU normally.
STEP 10. Replace the ETACS-ECU.
1. Replace the front-ECU.
2. The system should communicate with the front-ECU normally.
Q: Can the system communicate with the front-ECU?
YES: No action to be taken.
NO: Replace the ETACS-ECU. The system should communicate with the front-ECU normally.