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 a overdrive cancel signal.
When a malfunction of the auto-cruise control circuit occurs, the transmission 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)

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

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 "LOCK"(OFF) position before connecting or disconnecting scan tool MB991502.





1) Connect scan tool MB991502 to the data link connector.
2) Start the engine. (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 "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-117 <2.4L Engine> or C-119 <3.0L Engine> by backprobing.





1) Do not disconnect connector C-11 7 <2.4L Engine> or C-119 <3.0L Engine>.
2) Turn the ignition switch to "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 "LOCK"(OFF) position.
Q: Is the voltage normal?
YES: Go to Step 5.
NO: Go to Step 4.





STEP 4. Check connector C-117 <2.4L Engine> or C-119 <3.0L Engine, at PCM and C-25 at inter mediate connector for damage.
Q: Is the connector 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-21 by backprobing.





1) Do not disconnect connector C-21.
2) Turn the ignition switch to 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 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-117 <2.4L Engine> or C-119 <3.0L Engine> terminal 75 and autocruise control-ECU connector C-21 terminal 3.
Q: Is the harness wire in good condition?
YES: Go to Step 7.
NO: Repair it.





STEP 7. Check connector C-21 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.