System Description

The cruise control system associated with diesel engines includes the following components:
^ The powertrain control module (PCM)
^ The electronic throttle system
^ The vehicle speed sensor (VSS) buffer
^ The multifunction lever
^ The brake release switch The PCM operates in the following manner:
^ The PCM receives commands from the multifunction lever.
^ The PCM receives vehicle speed information from the VSS buffer.
^ The PCM sends information to the electronic throttle system in order to control vehicle speed.

Brake Release Switch
The PCM uses an electronic brake switch which contains one normally open contact and one normally closed contact. These switch contacts are part of the zero adjust brake switch.

When the brake pedal is depressed, the two brake switch contacts change input states at the PCM. The PCM then shuts off all of the cruise control outputs to the electronic throttle system.

Clutch Release Switch
For vehicles equipped with a manual transmission, the clutch release switch is on the clutch push-rod. When the clutch pedal is depressed, the clutch release switch activates and interrupts the voltage supply to the cruise control circuit in the engine control module, and disengages the cruise module.

Vehicle Speed Sensor
The VSS generates the vehicle speed signal at the transmission. The VSS buffer translates the vehicle speed signal.

The VSS mounts to the automatic transmission assembly. The VSS produces an AC signal. The frequency of this signal is proportional to the transmission output shaft speed. The AC goes to the VSS buffer for amplification and for conversion to a digital square wave that represents the vehicle speed in terms of pulses per mile (PPM). The VSS buffer provides a 4000-PPM signal.

This 4000-PPM signal is available to the PCM, and the speedometer in the instrument cluster.