Inspection Procedure 1
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 Part 1:
Auto-cruise Control-ECU Supply, Ground And Data Link Circuit Part 2:
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 (terminal number 6) 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 (terminal number 6).
Q: Is any harness wire between ignition switch and auto-cruise control-ECU connector C-20 (terminal number 6) 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 not 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 (terminal number 14) 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 (terminal number 14) and ground.
Q: Is any harness wire between auto-cruise control-ECU connector C-20 (terminal number 14) 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 not 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 (terminal number 13).
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 not 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 (terminal number 11) 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 (terminal number 11) and data link connector C-29 (terminal number 13).
Q: Is any harness wire between auto-cruise control-ECU connector C-20 (terminal number 11) and data link connector C-29 (terminal number 13) 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 not 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 not eliminated, replace the auto-cruise control-ECU. Then check that the malfunction is eliminated.