If A/C is turned on while engine is at idle, ECM will signal the Auxiliary Air Control (AAC) to increase idle speed. During hard acceleration, ECM cuts off the A/C power relay circuit to disengage A/C clutch for several seconds to aid acceleration.
Informs ECM when A/C system is on. ECM responds by increasing idle speed to improve idling and reduce emissions. During heavy engine load, ECM will also open the A/C clutch relay to disengage A/C clutch.
A/C Thermo Control Amplifier
Informs ECM of A/C system evaporator outlet temperature. Input helps determine cooling fan operation.
Throttle Position (TP) Sensor & Idle Switch
The TP sensor has a potentiometer which varies output voltage in response to changes in throttle position. This information is relayed to ECM in form of an input voltage signal on the 3-terminal TP sensor harness. TP sensor also has the ability to inform ECM of the rate of changes taking place in throttle plate movement. TP sensor is attached to throttle body housing and is actuated by movement of the accelerator pedal.
The idle switch is an integral part of the TP sensor. Switch is closed at idle and open during all other conditions. Switch is used to inform the ECM when the throttle is closed for fuel-cut on deceleration. Switch also has a full throttle position used only on vehicles equipped with an automatic transmission control unit.
Monday, May 4th, 2009 AT 5:40 AM