Fast Idle System Diagnosis

Fast Idle System Diagnosis

Refer to Engine Controls Schematics Cruise Control and PTO and CPP and Fast Idle Switches .

Circuit Description

Ignition positive voltage is supplied to the FAST IDLE request circuit by the PCM. The PCM monitors the voltage at the FAST IDLE request circuit. When the FAST IDLE switch is depressed the FAST IDLE request circuit is connected to ground and the voltage on the circuit is pulled down to near 0 volts. The PCM will activate or deactivate the FAST IDLE system as follows:

* The PCM will activate the FAST IDLE system if the following conditions exist:

- The PCM FAST IDLE parameters are programmed into the PCM
- The engine is running
- The vehicle speed is 0 km/h (0 mph)
Refer to Power Take-Off Fast Idle and Fast Idle System Programming Programming and Relearning.

* When the FAST IDLE system is activated the following actions are taken:

- The pre-determined engine speed is reached
The engine speed is controlled by the throttle actuator control (TAC) module. The engine speeds are determined by the PTO Options data list values that have been selected on the scan tool. Refer to Power Take-Off Fast Idle and Fast Idle System Programming Programming and Relearning.
- The FAST IDLE lamp control circuit is grounded by the PCM and the lamp is turned ON

* The PCM will deactivate the FAST IDLE system and turn the FAST IDLE lamp OFF if any of the following exist:

- The engine is not running
- The FAST IDLE switch is depressed and the voltage on the circuit is pulled down to near 0 volts
- The vehicle speed is above 0 km/h (0 mph)

Test Description

The number below refers to the step number on the diagnostic table.
3. The specific Fast Idle engine speed options can be displayed and modified on the scan tool and are to be used as a guide to determine if the Fast Idle system is functioning properly. Refer to Power Take-Off Fast Idle and Fast Idle System Programming Programming and Relearning.