1. Communication With Scan Tool Is Not Possible

INSPECTION PROCEDURE 1: Communication with Scan Tool MB991502 is not Possible (Communication with the Auto-cruise Control-ECU Only is not Possible).
















CIRCUIT OPERATION
Power of the auto-cruise control-ECU is transmitted from the ignition switch (IG1) to the auto-cruise control-ECU through junction block fuse number 21

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 signal voltage at auto-cruise control- ECU connector C-21 by backprobing.

1. Do not disconnect auto-cruise control-ECU connector C-21.
2. Turn the ignition switch to the ON position.
3. Measure the voltage between auto-cruise control-ECU connector C-21 terminal 6 and ground by backprobing.
- The voltage should measure battery positive voltage.
4. Turn the ignition switch to the LOCK (OFF) position.

Q: Is the measured voltage battery positive voltage?

YES: Go to Step 4.
NO: Go to Step 2.







STEP 2. Check auto-cruise control-ECU connector C-21 and Junction block connector C-308 and C-311 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connectors and terminals in good condition?

YES: Go to Step 3.
NO: Repair or replace the faulty connector. (Refer to Harness Connector Inspection). Go to Step 9.




STEP 3. Check the harness wire between ignition switch and auto-cruise control-ECU c6nnector C-21 terminal 6 for damage.

Q: Is the harness wire in good condition?

YES: It can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspect ion Service Points - How to Cope with Intermittent Malfunction). Go to Step 9.
NO: Go to Step 9.







STEP 4. Measure the ground circuit voltage at auto-cruise control-ECU connector C-21 by backprobing.

1. Do not disconnect auto-cruise control-ECU connector C-21.
2. Turn the ignition switch to the ON position.
3. Measure the voltage between auto-cruise control-ECU connector C-21 terminal 14 and ground by backprobing. The voltage should measure 0.5 volt or less.
4. Turn the ignition switch to the Lock (OFF) position.

Q: Is the measured voltage 0.5 volts or less?

YES: Go to Step 7.
NO: Go to Step 5.




STEP 5. Check auto-cruise control-ECU connector C-21 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is the connector and terminals in good condition?

YES: Go to Step 6.
NO: Repair or replace the faulty connector. (Refer to Harness Connector Inspection). Go to Step 9.




STEP 6. Check the harness wire between auto-cruise control-ECU connector C-21 terminal 14 and ground for damage.

Q: Is the harness wire in good condition?

YES: It can be assumed that this malfunction is intermittent.
(Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). Go to Step 9.
NO: Repair the damaged harness wire. Go to Step 9.







STEP 7. Check auto-cruise control-ECU connector C-21 and data link connector C-26 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connectors and terminal in good condition?

YES: Go to Step 8.
NO: Repair or replace the faulty connector. (Refer to Harness Connector Inspection). Go to Step 9.







STEP 8. Check the harness wire between auto-cruise control-ECU connector C-21 terminal 11 and data link connector C-26 terminal 13 for damage.

Q: Is the harness wire in good condition?

YES: Check that the malfunction is eliminated. If the malfunction is eliminated, it can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). If the malfunction is not eliminated, replace the auto-cruise control-ECU (go to Step 9.
NO: Repair the damaged harness wire. Go to Step 9.

STEP 9. Check that the malfunction is eliminated.

Q: Is the malfunction eliminated?

YES: This procedure is complete.
NO: Go to Step 1.