Envoy 4WD V8-5.3L VIN P (2004)
Cruise Control: Description and Operation
CRUISE CONTROL DESCRIPTION AND OPERATION
Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions at vehicle speeds above 40 km/h (25
mph). Steep grades may cause variations in the selected vehicle speeds.
The following are the main components of the cruise control system:
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The powertrain control module (PCM)
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The On/Off switch
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The Resume/Accel switch
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The Set/Coast switch
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The TCC/brake switch
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The stop lamp switch
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The throttle actuator control (TAC) module
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The vehicle speed sensor
Cruise Control Engaged
The TAC module monitors the signal circuits of the following cruise control switches:
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On/Off
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Resume/Accel
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Set/Coast
The cruise control switches are located on the multifunction/turn signal lever.
The PCM will engage and adjust vehicle speed based on the information received from the TAC module via the UART serial data link. For further
information on the TAC system, refer to Throttle Actuator Control (TAC) System Description in Computers and Control Systems 4.8L, 5.3L, and
6.0L.
Ignition positive voltage is supplied from the 10 ampere CRUISE fuse to the cruise control switch via the ignition 3 voltage circuit. When the
normally open cruise control On/Off switch is turned On, the switch closes and the TAC module detects a high signal voltage on the cruise control on
switch signal circuit. When the normally open Set/Coast switch is pressed, the switch closes and the TAC module detects a high signal voltage on the
cruise control set/coast switch signal circuit. To engage the cruise control system, turn the On/Off switch On and momentarily press the Set/Coast
switch. The TAC sends a UART message to the PCM, in order to confirm that the cruise control enable criteria has been met.
The PCM will engage the cruise control system and record the selected vehicle speed. The PCM sends a class 2 message to the instrument panel
cluster in order to illuminate the cruise control indicator. Pressing the accelerator pedal, while the cruise control system is engaged, will allow the
driver to override the cruise control system in order to accelerate the vehicle beyond the current set vehicle speed. When the accelerator pedal is
released, the vehicle will decelerate and resume the current set vehicle speed. The driver can also override the current set vehicle speed via the
Set/Coast switch and the Resume/Accel switch. When the cruise control system is engaged, pressing and holding the Set/Coast switch will allow the
vehicle to decelerate from the current set vehicle speed without deactivating the cruise control system. When the Set/Coast switch is released, the
PCM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged,
momentarily pressing the Set/Coast switch will allow the vehicle to decelerate at 1.6 km/h (1 mph) increments for each time that the Set/Coast is
momentarily pressed, with a minimum vehicle speed of 37 km/h (23 mph). When the normally open Resume/Accel switch is activated, the switch
closes and the TAC module detects a high signal voltage on the cruise control resume/accel switch signal circuit. Activating and holding the
Resume/Accel switch, when the cruise control system is engaged, will allow the vehicle to accelerate to a greater vehicle speed than the current set
vehicle speed. When the Resume/Accel switch is released, the PCM will record the vehicle speed and maintain the vehicle speed as the new set
vehicle speed. When the cruise control system is engaged, momentarily activating the Resume/Accel switch will allow the vehicle to accelerate at 1.6
km/h (1 mph) increments for each time that the Resume/Accel switch is momentarily activated, with the maximum acceleration total of 16 km/h (10
mph) over the current set vehicle speed. Momentarily activating the Resume/Accel switch, after the cruise control system has been disengaged by
pressing the brake pedal, will recall the previous set vehicle speed that is recorded in the PCM.
Cruise Control Disengaged
The PCM disengages the cruise control operation based on the information received from the TAC module. The TAC module monitors the signal
circuits of the following switches:
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The On/Off switch
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The TCC/brake switch
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The stop lamp switch
The TCC brake switch and the stop lamp switch are incorporated into an assembly and are mounted to the brake pedal bracket. Pressing the brake
pedal while the cruise control is engaged will disengaged the cruise control system. The TAC module monitors the stop lamp switch signal circuit and
the PCM monitors the TCC brake switch/cruise control release signal circuit. When the brake pedal is pressed, the normally closed TCC brake switch
opens and the normally open stoplamp switch closes. The TAC module detects a high signal voltage on the stop lamp switch signal circuit and the
PCM detects a low signal voltage on the TCC brake switch/cruise control release signal circuit. The TAC module sends a UART message to the PCM
indicating the status of the stop lamp switch. The cruise control system will disengage when the cruise control On/Off switch is turned Off. The
vehicle speed stored in the memory of the PCM will be erased when the cruise control On/Off switch is turned to Off, or the ignition switch is turned
