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. Measure the output circuit voltage at auto-cruise control-ECU connector C-113 (terminal 6) by backprobing.
1. Do not disconnect auto-cruise control switch connector C-113.
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-113.
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-203 and C-205.
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-113 (terminal 6).
Q: Is any harness wire between ignition switch and auto-cruise control-ECU connector C-113 (terminal 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. Measure the ground circuit voltage at auto-cruise control-ECU connector C-113 (terminal 14) by backprobing.
1. Do not disconnect auto-cruise control switch connector C-113.
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-113
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-113 (terminal 14) and ground.
Q: Is any harness wire between auto-cruise control-ECU connector C-113 (terminal 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 data link connector C-23 and auto-cruise control-ECU connector C-113.
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 9.
STEP 9. Check the harness wire between data link connector C-23 (terminal 13) and auto-cruise control-ECU connector C-113 (terminal 11).
Q: Is any harness wire between data link connector C-23 (terminal 13) and auto-cruise control-ECU connector C-113 (terminal 11) 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. (Refer to.) Then check that the malfunction is eliminated.