Inspection Procedure 16

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

Part 1 Of 2:

Part 2 Of 2:

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:
^ MB991958: Scan Tool (MUT-III Sub Assembly)
^ MB991824: V.C.I.
^ MB991827: MUT-III USB Cable
^ MB991911: MUT-III Main Harness B

STEP 1. Using scan tool MB991958, check data list item 66: Overdrive Off Signal (Auto-cruise ECM Signal).

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1) Connect scan tool MB991958 to the data link connector.
2) Start the engine and prepare to test drive the vehicle. (Operate the auto-cruise)
3) Set scan tool MB991958 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: It can be assumed that this malfunction can be intermittent.
NO: Go to Step2.

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-57 <2.4L Engine> or C-59 <3.0L Engine> by backprobing.

1) Do not disconnect connector C-57 <2.4L Engine> or C-59 <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 PCM connector C-57 <2.4L Engine> or C-59 <3.0L Engine> and inter mediate connector C-28 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-57 <2.4L Engine> or C-59 <3.0L Engine> terminal 75 and auto-cruise control-ECU connector C-20 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-20 by backprobing.

1) Do not disconnect connector C-20.
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-20 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 auto-cruise control-ECU connector C-20 and inter mediate connector C-28 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-57 <2.4L Engine> or C-59 <3.0L Engine> terminal 75 and auto-cruise control-ECU connector C-20 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 MB991958, check data list item 66: Overdrive Off Signal (Auto-cruise control-ECU Signal).

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.