Inspection Procedure 27

Improper Idle Speed When the A/C is Operating (A/C load signal)

A/C Load Signal Circuit:

CIRCUIT OPERATION
- The PCM increases the engine idle speed by driving the throttle actuator control motor when the automatic compressor-ECU sends an "A/C on" signal to the PCM.
- 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 load signal". The PCM receives this A/C load signal from the A/C-ECU through terminal No. 78, and determines the idle-up speed according to the 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.
- PCM failed.

DIAGNOSIS




STEP 1. Check connector C-112 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 PCM connector C-112 by backprobing.




1. Do not disconnect connector C-112. 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. 78 and ground.
- If atmospheric air temperature is 15 °C (59 °F) or less, the voltage should be 1 volt or less.
- If atmospheric air temperature is 18 °C (65.4 °F) more, the voltage should be 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 PCM. Then confirm that the malfunction symptom is eliminated.

NO: Refer to Introduction To Heater, Air Conditioning And Ventilation Diagnosis.