Fast Idle System Description

Fast Idle System Description

Fast Idle

Fast Idle (UF3) is available on heavy duty engines equipped with cruise control. The purpose of fast idle is to increase engine idle speed. The system is controlled through the steering wheel mounted cruise control switches. Upon activation a signal is sent through the body control module (BCM) to the engine control module (ECM) commanding an increase in engine speed.

The instrument panel will indicate the fast idle system is active by displaying a message across the driver information center (DIC).

Fast Idle Enable and Disable

To enable the fast idle system, perform the following procedure:

1. Engine running.

2. Park brake set.

3. Transmission shifter in P (park) or N (neutral).

4. Press and release the cruise control ON/OFF button.

5. Press and release the cruise control SET button.

When the procedure is followed the engine idle speed will increase to approximately 1,200 RPM.

The manual fast idle system will be disabled if any of the following procedures are performed:

* Brake applied

* Cruise control CANCEL, ON/OFF, or SET buttons depressed

* Park brake released

* Accelerator pedal depressed more than 25%

* Clutch applied

* Ignition switch turned to the LOCK/OFF position