Inspection Procedure A-4

Communication with the Front-ECU is Impossible.

NOTE: This troubleshooting requires use of scan tool MB991958 and SWS monitor kit MB991862. For details of how to use the SWS monitor, refer to "How to use SWS monitor." How To Use SWS Monitor

Front-ECU Power Supply And SWS Communication Circuit Part 1:

Front-ECU Power Supply And SWS Communication Circuit Part 2:

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 7 of the front-ECU) is damaged, also check the power supply circuit from the ignition switch (IG2) (terminal 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: Harness Set
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: Vehicles communication interface
- MB991827: MUT-III USB cable
- MB991911: MUT-III Main harness B
- MB991813: SWS monitor kit
- MB991806: SWS monitor cartridge
- MB991812: SWS monitor harness (for column-ECU)
- MB991922: Probe harness

STEP 1. Use scan tool MB991958 to select "ECU COMM Check" on the SWS monitor display.
Check the ETACS-ECU.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958. Connect special tool MB991911 before connecting special tool MB991812. Be sure to connect special tool MB991806 after turning on special tool MB991824.







1. Connect the special tool. Refer to "How to connect SWS monitor How to Connect SWS Monitor."
2. Turn the ignition switch to the "LOCK" (OFF) position.
3. Operate scan tool MB991958 according to the procedure below to display "ECU COMM Check."
a. Select "Interactive Diagnosis."
b. Select "System Select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "ECU COMM Check."

4. Scan tool MB991958 should show "OK" on the "ECU COMM Check" menus for both the "ETACS ECU" menus.

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 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 (terminal 7) and the battery.

Q: Is the wiring harness between front-ECU connector A-10X (terminal 7) 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 (terminal 31) and the ground.

Q: Is the wiring harness between front-ECU connector A-11X (terminal 31) 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-118 for damage.

Q: Are front-ECU connector A-11X and ETACS-ECU connector C-118 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 (terminal 22) and ETACS-ECU connector C-118 (terminal 59).

NOTE: Also check joint connector C-78 and intermediate connector C-89. If joint connector C-78 or intermediate connectors C-89 is damaged, repair or replace the connector as described in Harness Connector Inspection.

Q: Is the wiring harness between front-ECU connector A-11X (terminal 22) and ETACS-ECU connector C-118 (terminal 59) 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.