With Automatic Transmission

Circuit Description
The Powertrain Control Module (PCM) receives Electrical Load Idle-up signals from the HVAC blower motor, exterior lighting (headlights), and the rear window defogger circuits. When the electrical load idle-up signal is present, the PCM increases the Idle Air Control (IAC) valve opening. Increasing the Idle Air Control valve opening enables the engine to maintain the idle speed necessary to compensate for the additional electrical load. The idle-up signal of the rear window defogger circuit (four door vehicles only) passes through an electrical load diode. The electrical load diode is located below the glove box, behind the PCM.

Diagnostic Aids
If the scan tool indicates that the IAC Duty Cycle is increasing, but the idle quality is unsatisfactory, inspect the IAC system for proper operation.

Check for a faulty electrical connection to the PCM.

An intermittent malfunction may be caused by a fault in one of the Electrical Load Idle-up circuits. 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.

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step checks whether the PCM is responding to the electrical load idle-up inputs by commanding the IAC valve to increase the IAC Duty Cycle percentage. The IAC Duty Cycle parameter on the scan tool should increase 2 to 3 percent when operating the accessory. If the scan tool does not indicate an increase in the IAC Duty Cycle when the accessory is turned ON, the PCM may not be receiving the idle-up signal.
7. This step checks for a fault in the circuit between the PCM and the electrical load diode. The electrical load diode is located below the glove box and behind the PCM.