For 1990-2009 cars
Cell 20: Idle Air Control
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

This signal is sent from the A/C compressor control module. The powertrain control module (PCM) detects whether or not the A/C system is operating via the A/C compressor control module. The extra load the A/C system demands from the engine requires a higher idle speed. When the PCM receives the A/C ON signal, it will activate the Idle Air Control (IAC) valve and the idle speed will increase.

### Diagnostic Aids

An intermittent malfunction may be caused by a fault in the A/C sensor circuit. Inspect the wiring harness and components for any of the following conditions:

• | Backed out terminals.

• | Improper mating of terminals.

• | Broken electrical connector locks.

• | Improperly formed or damaged terminals.

• | Faulty terminal to wire connections.

• | Physical damage to the wiring harness.

• | A broken wire inside the insulation.

• | Corrosion of electrical connections, splices, or terminals.

Use a scan tool in order to monitor the A/C switch parameter. When the A/C switch is in the ON position and the blower speed is in any speed except OFF, the scan tool should read ON. When the A/C switch is OFF, the scan tool should read OFF.

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. This step checks for an open or a short to ground in the YEL/BLK wire, or a faulty PCM.

2. This step checks for a faulty PCM or for a faulty A/C compressor control module.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn OFF the ignition.
2. Disconnect the A/C compressor control module electrical connector.
3. Turn ON the ignition.
4. Using a DMM, measure the voltage from the A/C compressor control module connector cavity 1.

Does the DMM read within the specified value?

B+

Go to Step 3

Go to Step 4

3 |

1. Turn OFF the ignition.
2. Reconnect the A/C compressor control module electrical connector.
3. Start the engine.
4. Press the A/C switch to ON and move the blower speed selector switch to any position except OFF.
5. Using a DMM, back probe the A/C compressor control module connector cavity 1.
6. Measure the voltage.

Does the DMM read within the specified value?

0 volts

System OK

Go to Step 5

4 |

1. Check for an open or a short in the A/C ON signal circuit between the A/C compressor control module and the PCM.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 7

Go to Step 6

5 | Replace the A/C compressor control module. Refer to Air Conditioning. Is the action complete? | -- | Go to Step 7 | --
6 | Replace the PCM. Refer to Powertrain Control Module Replacement Is the action complete? | -- | Go to Step 7 | --
7 | Operate the vehicle within the conditions under which the original symptom was noted. Does the system now operate properly? | -- | System OK | Go To Diagnostic Aids