Inspection Procedure 15: Vehicle Shifts Differently With A/C Engaged

INSPECTION PROCEDURE 15: Vehicle Shifts Differently with A/C Engaged




















CIRCUIT OPERATION
^ When the A/C is turned ON and the dual pressure switch is closed, PCM (terminal number 83) receives battery voltage and then determines the A/C compressor has been signaled to engage.
^ When the A/C compressor is engaged, the PCM increases line pressure and briefly delays shift points to compensate for the additional engine load.

COMMENT
The cause is probably a faulty dual pressure switch circuit or a defective PCM.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CASE:)
^ Malfunction of the dual pressure switch
^ Damaged harness, connector
^ Malfunction of A/C system
^ Malfunction of the PCM

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

STEP 1. Using scan tool MB991502, check data list item 65: Dual Pressure Switch.

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 run at idle.
3 Set scan tool MB991502 to data reading mode for item 65: Dual Pressure Switch.
^ When the A/C is in operation, the scan tool MB991502 display should be "ON."
^ When the A/C is not in operation, the scan tool MB991502 display should be "OFF."
4 Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the switch operating properly?
YES: It can be assumed that this malfunction is intermittent.
NO: Go to Step 2.

STEP 2. Check dual pressure switch connector A-36 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 damaged components.

STEP 3. Measure the power supply voltage at dual pressure switch connector A-36.





1 Disconnect the connector A-36 and measure at the harness side.
2 Start the engine and run at idle.
3 Operate the A/C.





4 Measure the voltage between terminal 2 and ground.
^ Voltage should measure battery positive voltage.
5 Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the measured voltage battery positive voltage?
YES: Go to Step 10.
NO: Go to Step 4.

STEP 4. Measure the power supply voltage at automatic compressor controller connector C-14 by backprobing.





1 Do not disconnect connector C-14.
2 Start the engine and run at idle.
3 Operate the A/C.





4 Measure the voltage between terminal 4 and ground by backprobing.
^ Voltage should measure battery positive voltage.
5 Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the measured voltage battery positive voltage?
YES: Go to Step 8.
NO: Go to Step 5.

STEP 5. Check intermediate connector C-212 and automatic compressor controller connector C-14 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 6.
NO: Repair or replace the damaged components.

STEP 6. Check the harness for short circuit to ground between dual pressure switch connector A-36 terminal 2 and automatic compressor controller connector C-14 terminal 4.








Q: Is the harness wire in good condition?
YES: Go to Step 7.
NO: Repair or replace the harness wire.

STEP 7. Using scan tool MB991502, check data list item 65: Dual Pressure Switch.

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 run at idle.
3 Set scan tool MB991502 to data reading mode for item 65: Dual Pressure Switch.
^ When the A/C is in operation, the scan tool display should be "ON."
^ When the A/C is not in operation, the scan tool display should be "OFF."
4 Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the switch operating properly?
YES: It can be assumed that this malfunction is intermittent.
NO: Check the air conditioning system.

STEP 8. Check intermediate connector C-212 and automatic compressor controller connector C-14 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 9.
NO: Repair or replace the damaged components.

STEP 9. Check the harness for open circuit between dual pressure switch connector A-36 terminal 2 and automatic compressor controller connector C-14 terminal 4.








Q: Is the harness wire in good condition?
YES: Go to Step 14.
NO: Repair or replace the harness wire.

STEP 10. Measure the switch output 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 Start the engine and run at idle.
3 Operate the A/C.





4 Measure the voltage between terminal 83 and ground by backprobing.
^ When the A/C is in operation, the voltage should measure battery positive voltage.
5 Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the measured voltage battery positive voltage?
YES: Go to Step 15.
NO: Go to Step 11.

STEP 11. Check intermediate connectors C-25, C-212 and PCM connector C-117 <2.4L Engine> or C-119 <3.0L Engine> 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 12.
NO: Repair or replace the damaged components.

STEP 12. Check harness for open circuit or short circuit to ground between dual pressure switch connector A-36 terminal 1 and PCM connector C-117 <2.4L Engine> or C-119 <3.0L Engine> terminal 83.








Q: Is the harness wire in good condition?
YES: Go to Step 13.
NO: Repair or replace the harness wire.

STEP 13. Check the dual pressure switch.
Q: Is the switch operating properly?
YES: Go to Step 14.
NO: Replace the dual pressure switch.

STEP 14. Using scan tool MB991502, check data list item 65: Dual Pressure Switch.

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 run at idle.
3 Set scan tool MB991502 to data reading mode for item 65:
Dual Pressure Switch.
^ When the A/C is in operation, the scan tool display should be "ON."
^ When the A/C is not in operation, the scan tool display should be "OFF."
4 Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the switch operating properly?
YES: It can be assumed that this malfunction is intermittent.
NO: Replace the PCM.

STEP 15. Check PCM connector C-117 <2.4L Engine> or C-119 <3.0L Engine> 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 14.
NO: Repair or replace the damaged components.