Inspection Procedure 16

INSPECTION PROCEDURE 16: Transaxle won't Downshift under Load with Auto-cruise Engaged.






CIRCUIT OPERATION
When the battery positive voltage from PCM (terminal number 75) is grounded at auto-cruise control-ECU (terminal number 3), the auto-cruise control-ECU emits an overdrive cancel signal. When a malfunction of the auto-cruise control circuit occurs, the transaxle may downshift harshly with the auto-cruise control engaged.

COMMENT
A malfunction may be present on the auto-cruise signal line circuit, auto cruise control ECU or the PCM.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set:)
^ Damaged harness, connector
^ Malfunction of the PCM
^ Malfunction of the auto-cruise control ECU

DIAGNOSIS

Required Special Tool: MB991502: Scan Tool (MUT-II)





STEP 1. Using scan tool MB991502, check data list item 66: Overdrive Off Signal (Auto-cruise ECM Signal).

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool M8991502.

1. Connect scan tool MB991502 to the data link connector.
2. Start the engine and prepare to test drive the vehicle. (Operate the auto-cruise)
3. Set scan tool MB991502 to data reading mode for item 66: Overdrive Off Signal (Auto-cruise ECM Signal).
^ When driving at level road, the display should be "OFF."
^ When driving at uphill road, the display should be "ON."
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: This malfunction can be intermittent.
NO: Go to Step 2.

STEP 2. Check the auto-cruise system. Check the auto-cruise system.
Q: Is the auto-cruise system operating properly?
YES: Go to Step 3.
NO: Repair it, then check the symptom.

STEP 3. Check the signal voltage at PCM connector C-116 by backprobing.





1. Do not disconnect connector C-116.
2. Turn the ignition switch to the "ON" position.





3. Measure the voltage between terminal 75.and ground by backprobing.
^ Voltage should be battery positive voltage.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 5.
NO: Go to Step 4.





STEP 4. Check connector C-116 connector for damage.
Q: Are the connectors in good condition?
YES: Replace the PCM.
NO: Repair or replace it.

STEP 5. Check the signal voltage at auto-cruise control-ECU connector C-107 by backprobing.





1. Do not disconnect connector C-107.
2. Turn the ignition switch to the "ON" position.





3. Measure the voltage between terminal 3 and ground by backprobing.
^ Voltage should be battery positive voltage.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 7.
NO: Go to Step 6.








STEP 6. Check harness for short circuit to ground, open circuit or damage between PCM connector C-116 terminal 75 and auto-cruise control-ECU connector C-107 terminal 3.
Q: Is the harness wire in good condition?
YES: Go to Step 7.
NO: Repair it.





STEP 7. Check connector C-107 at auto-cruise control-ECU connector for damage.
Q: Is the connector in good condition?
YES: Replace the auto-cruise control-ECU.
NO: Repair or replace it.