Inspection Procedure 16: Transaxle Won't Downshift Under Load With Auto-Cruise Engaged.

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 CASE:)
^ 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 control-ECU 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 MB991502.





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 control-ECU 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: It can be assumed that 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. Measure the signal voltage at PCM connector C-117 <2.4L Engine> or C-119 <3.0L Engine> by backprobing.





1 Do not disconnect connector C-117 <2.4L Engine> or C-119 <3.0L Engine>.
2 Turn the ignition switch to the "ON" position.





3 Measure the voltage between terminal 75 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 6.
NO: Go to Step 4.

STEP 4. Check inter mediate connector C-25 and PCM connector C-117 <2.4L Engine> or C-119 <3.0L Engine> for looser, corroded or damaged terminals, or terminals pushed back in the connector.








Q: Are the connectors and terminals in good condition?
YES: Go to Step 5.
NO: Repair or replace the damaged components.

STEP 5. Check the harness for open circuit, short circuit to ground or damage between PCM connector C-117 <2.4L Engine> or C-119 <3.0L Engine> terminal 75 and auto-cruise control-ECU connector C-21 terminal 3.








Q: Is the harness wire in good condition?
YES: Go to Step 6.
NO: Repair or replace the harness wire.

STEP 6. Measure the signal voltage at auto-cruise control-ECU connector C-21 by backprobing.





1 Do not disconnect connector C-21.
2 Turn the ignition switch to the "ON" position.





3 Measure the voltage between terminal 3 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 7.
NO: Go to Step 8.

STEP 7. Check auto-cruise control-ECU connector C-21 at for looser, corroded or damaged terminals, or terminals pushed back in the connector.





Q: Are the connector and terminals in good condition?
YES: Go to Step 10.
NO: Repair or replace the damaged components.

STEP 8. Check inter mediate connector C-25 and auto-cruise control-ECU connector C-21 for looser, corroded or damaged terminals, or terminals pushed back in the connector.








Q: Are the connectors and terminals in good condition?
YES: Go to Step 9.
NO: Repair or replace the damaged components.

STEP 9. Check harness for short circuit to ground between PCM connector C-117 <2.4L Engine> or C-119 <3.0L Engine> terminal 75 and auto-cruise control-ECU connector C-21 terminal 3.








Q: Is the harness wire in good condition?
YES: Go to Step 10.
NO: Repair or replace the harness wire.

STEP 10. Using scan tool MB991502, check data list item 66: Overdrive Off Signal (Auto-cruise control-ECU 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 MB991502.





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 control-ECU 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: It can be assumed that this malfunction can be intermittent.
NO: Replace the PCM.