1. Communication With Scan Tool Not Possible

Communication with Scan Tool MB991502 is not Possible (Communication with the Auto-cruise Control-ECU Only is not Possible.)

Auto-cruise Control-ECU Supply, Ground And Data Link Circuit:

Connector:

CIRCUIT OPERATION
Power of the auto-cruise control-ECU is transmitted from the ignition switch (IG1) to the auto-cruise control-ECU through multi-purpose fuse 4 in the junction block.

TECHNICAL DESCRIPTION (COMMENT)
The cause is probably a malfunction of the auto-cruise control-ECU power supply circuit or the auto-cruise control-ECU ground circuit.

TROUBLESHOOTING HINTS
- Damaged harness or connector.
- Malfunction of the auto-cruise control-ECU.

DIAGNOSIS

Required Special Tool:
- MB991223: Harness Set

STEP 1. Check the output circuit voltage at auto-cruise control-ECU connector C-20 by backprobing.
1. Do not disconnect auto-cruise control switch connector C-20.
2. Turn the ignition switch to the "ON" position.




3. Measure the voltage between terminal 6 and ground by backprobing.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the voltage approximately battery positive voltage?

YES: Go to Step 5.

NO: Go to Step 2.




STEP 2. Check auto-cruise control-ECU connector C-20.

Q: Is the connector damaged?

YES: Repair or replace connector. Refer to Harness Connector Inspection. Then check that the malfunction is eliminated.

NO: Go to Step 3.




STEP 3. Check junction block connector C-108 and C-111.

Q: Is any connector damaged?

YES: Repair or replace connector. Refer to Harness Connector Inspection. Then check that the malfunction is eliminated.

NO: Go to Step 4.




STEP 4. Check the harness wire between ignition switch and auto-cruise control-ECU connector C-20.

Q: Is any harness wire between ignition switch and auto-cruise control-ECU connector C-20 damaged?

YES: Repair the harness wire and then check that the malfunction is eliminated.

NO: Check that the malfunction is eliminated. If the malfunction is eliminated, replace the auto-cruise control-ECU. Then check that the malfunction is eliminated.

STEP 5. Check the ground circuit voltage at auto-cruise control-ECU connector C-20 by backprobing.
1. Do not disconnect auto-cruise control switch connector C-20.
2. Turn the ignition switch to the "ON" position.




3. Measure the voltage between terminal 14 and ground by backprobing.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the voltage approximately 0.5 volts or less?

YES: Go to Step 8.

NO: Go to Step 6.




STEP 6. Check auto-cruise control-ECU connector C-20.

Q: Is the connector damaged?

YES: Repair or replace connector. Refer to Harness Connector Inspection. Then check that the malfunction is eliminated.

NO: Go to Step 7.




STEP 7. Check the harness wire between auto-cruise control-ECU connector C-20 and ground.

Q: Is any harness wire between auto-cruise control-ECU connector C-20 and ground damaged?

YES: Repair the harness wire and then check that the malfunction is eliminated.

NO: Check that the malfunction is eliminated. If the malfunction is eliminated, replace the auto-cruise control-ECU. Then check that the malfunction is eliminated.




STEP 8. Check the output circuit voltage at data link connector C-29.
1. Turn the ignition switch to the "ON" position.
2. Measure the voltage between terminal 13 and ground.
3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the voltage approximately 4 volts or more?

YES: Check that the malfunction is eliminated. If the malfunction is eliminated, replace the auto-cruise control-ECU. Then check that the malfunction is eliminated.

NO: Go to Step 9.




STEP 9. Check data link connector C-29.

Q: Is the connector damaged?

YES: Repair or replace connector. Refer to Harness Connector Inspection. Then check that the malfunction is eliminated.

NO: Go to Step 10.

STEP 10. Check the output circuit voltage at auto-cruise control-ECU connector C-20 by backprobing.
1. Do not disconnect auto-cruise control switch connector C-20.
2. Turn the ignition switch to the "ON" position.




3. Measure the voltage between terminal 11 and ground by backprobing.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the voltage approximately 4 volts or more?

YES: Go to Step 11.

NO: Go to Step 12.







STEP 11. Check the harness wire between auto-cruise control-ECU connector C-20 and data link connector C-29.

Q: Is any harness wire between auto-cruise control-ECU connector C-20 and data link connector C-29 damaged?

YES: Repair the harness wire and then check that the malfunction is eliminated.

NO: Check that the malfunction is eliminated. If the malfunction is eliminated, replace the auto-cruise control-ECU. Then check that the malfunction is eliminated.




STEP 12. Check auto-cruise control-ECU connector C-20.

Q: Is the connector damaged?

YES: Repair or replace connector. Refer to Harness Connector Inspection. Then check that the malfunction is eliminated.

NO: Check that the malfunction is eliminated. If the malfunction is eliminated, replace the auto-cruise control-ECU. Then check that the malfunction is eliminated.