Inspection Procedure 27

Incorrect Idle Speed When The A/C is Operating (A/C Switch 2 Signal)

A/C Switch 2 Signal Circuit:

CIRCUIT OPERATION
- The ECM 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 A/C-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 receives this A/C switch 2 signal from the automatic compressor controller through terminal No. 24, and determines the idle-up speed according to the high or low air conditioning load.

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

DIAGNOSIS




STEP 1. Check connector C-121 at ECM 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-121.




1. Disconnect the connector C-121 and measure at the harness side.
2. Start the engine and run at idle.
3. Turn the A/C switch "ON".




4. Measure the voltage between terminal No. 24 and ground.
- 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) 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. Then confirm that the malfunction symptom is eliminated.

NO: Refer to Heater, Air Conditioning And Ventilation - Manual A/C Diagnosis - Symptom Chart.