Inspection Procedure 27

A/C Switch 2 Signal Circuit:

Connectors:

or PCM increases the engine idle speed by driving the IAC motor when the automatic compressor-ECU sends a "A/C on" signal to the module.
- The automatic compressor-ECU detects how the air conditioning is applying load to the engine, and converts the information to a voltage signal (High voltage = low load, Low voltage = high load). This voltage signal is called "A/C switch 2 signal". The ECM or PCM receives this A/C switch 2 signal from the automatic compressor-ECU through terminal No. 65 or terminal No. 61 , and determines the idle-up speed according to the high or low air conditioning load.

TROUBLESHOOTING HINTS (The most likely causes for this case: )
- Malfunction of the A/C control system.
- Open or shorted circuit, or improper connector contact.
- ECM or PCM failed.

DIAGNOSIS

STEP 1. Check connector C-118 at ECM or connector C-115 at PCM for damage.

Q: Is the connector in good condition?

YES: Go to Step 2.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.

STEP 2. Measure the output voltage at ECM harness side connector C-118 or PCM harness side connector C-115 .

1. Do not disconnect the connector C-118 or C-115 .
2. Start the engine and run at idle.
3. Turn the A/C switch "ON".

4. Measure the voltage between terminal No. 65 or No. 61 and ground by backprobing.
- If atmospheric air temperature is 15° C (59° F) or less, the voltage should measure 1 volt or less.
- If atmospheric air temperature is 18° C (65.4° F) or more, the voltage should measure battery positive voltage.
5. Turn the A/C switch "OFF".
6. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage within the specified range?

YES: Replace the ECM or PCM. Then confirm that the malfunction symptom is eliminated.
NO: Refer to Introduction To Heater, Air Conditioning And Ventilation Diagnosis.