Inspection Procedure 15
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 code to be set:)
^ 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 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 properly7
YES: This malfunction is intermittent.
NO: Go to Step 2.
STEP 2. Check connector A-25 at dual pressure switch for damage.
Q: Is the connector in good conditions
YES: Go to Step 3.
NO: Repair or replace it.
STEP 3. Check the power supply voltage at dual pressure switch connector A-25.
1. Disconnect the connector A-25 and measure at the harness side.
2. Start the engine and run at idle.
3. Measure the voltage between terminal 2 and ground.
^ 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 9.
NO: Go to Step 4.
STEP 4. Check the power supply voltage at A/C-ECU connector C-16 by backprobing.
1. Do not disconnect connector C-16.
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 be battery positive voltage.
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 8.
NO: Go to Step5.
STEP 5. Check connectors C-16 at A/C-ECU and C-111 at intermediate connector for damage.
Q: Are the connectors in good condition?
YES: Go to Step 6.
NO: Repair or replace it.
STEP 6. Check harness for short circuit to ground between dual pressure switch connector A-25 terminal 2 and A/C-ECU connector C-16 terminal 4.
Q: Is the harness wire in good condition?
YES: Go to Step 7.
NO: Repair it.
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: This malfunction is intermittent.
NO: Check the air conditioning system.
STEP 8. Check connectors C-16 at A/C-ECU and C-111 at intermediate connector for damage.
Q: Are the connectors in good condition?
YES: Repair harness open circuit between A/C-ECU connector C-16 terminal 4 and dual pressure switch connector A-25 terminal 2.
NO: Repair or replace the defective connectors.
STEP 9. Check the switch output voltage at PCM connector C-116 by backprobing.
1. Do not disconnect connector C-116.
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 be battery positive voltage.
^ When the A/C is not in operation, the voltage should be 0.5 volt or less.
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 14.
NO: Go to Step 10.
STEP 10. Check connectors C-116 at PCM and C-111, C-122 at intermediate connector for damage.
Q: Are the connectors in good condition?
YES: Go to Step 11.
NO: Repair or replace it.
STEP 11. Check harness for short circuit to ground or open circuit between dual pressure switch connector A-25 terminal 1 and PCM connector C-116 terminal 83.
Q: Is the harness wire in good condition?
YES: Go to Step 12.
NO: Repair it.
STEP 12. Check the dual pressure switch.
Q: Is the switch operating properly?
YES: Go to Step 13.
NO: Replace the dual pressure switch.
STEP 13. 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: This malfunction is intermittent.
NO: Replace the PCM.
STEP 14. Check connector C-116 at PCM for damage.
Q: Is the connector in good condition?
YES: Go to Step 13.
NO: Repair or replace it.