Electrical Load Idle-Up Signals

The PCM receives several electrical load signals from various components. The PCM will adjust the engine idle speed, and sometimes the ignition timing, when receiving the electrical load input. The PCM will signal the Idle Air Control (IAC) Valve to open the idle air passage. Opening the idle air passage slightly will maintain an engine speed that provides a desirable idle. The PCM will return the engine to the original idle speed when the electrical load signal is removed. Depending on options, the vehicle will have at least some of the following electrical load inputs:
^ HVAC blower motor switch - This input affects engine speed and ignition timing.
^ Rear window defogger switch - This signal passes through an electrical load diode before reaching the PCM. This input affects engine speed and ignition timing. The electrical load diode is taped to the wiring harness and is located behind the PCM, below the glove box.
^ Exterior lights switch - This input affects the engine speed. On M/T equipped vehicles this signal passes through an electrical load diode before reaching the PCM. The electrical load diode is taped to the wiring harness and is located behind the PCM, below the glove box.