Inspection Procedure 28

A/C Switch 2 Signal Circuit:

or PCM increases the engine idle speed by driving the IAC motor when the automatic compressor-ECU sends an "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 24 or 61 , respectively. Then the ECM or PCM 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.
- Improper connector contact, open circuit or short-circuited harness wire.
- ECM failed.
- PCM failed.

DIAGNOSIS

STEP 1. Check voltage at ECM connector C-49 or PCM connector C-54 .
When the following conditions are satisfied, measure voltage between terminal number 24 or 61 and ground. Do not disconnect the connector during this measurement.
a. Engine: Warm at idle
b. Ambient temperature: 25°C (77°F) or more
Standard value: 0 - 3 volts
(A/C temperature control: Maximum cooling position)
Battery positive voltage
(A/C temperature control: Maximum heating position)

If within the specifications, go to Step 2.

If not within the specifications, check the A/C system. Refer to Heater, Air Conditioning and Ventilation

Diagnosis - Introduction to Heater, Air Conditioning and Ventilation Diagnosis.

STEP 2. Check harness connector C49 at the ECM or harness connector C-54 at the PCM for damage.
If harness connector C-49 or C-54 is not damaged, replace the ECM or PCM.

If harness connector C-49 or C-54 is damaged, repair or it. Refer to Harness Connector Inspection.

Then check that the malfunction is eliminated.