Cruise Control Description and Operation 3.4L
Cruise control is a speed control system that maintains a desired vehicle speed
under normal driving conditions at speeds above 40km/h (25 mph). However, steep
grades may cause variations in the selected speeds. The main components of the cruise
control system are:
| • | The cruise control module assembly |
| • | The cruise control switches |
| • | The cruise control release switch |
| • | The powertrain control module (PCM) |
| • | The stoplamp switch assembly |
| • | The vehicle speed sensor |
The cruise control system has the capability to adjust speeds and disengage
the system based on the activation of the following cruise control switches:
The cruise control module controls the operation of the cruise control system.
The cruise control module monitors the signal circuits of the cruise control switches.
When the normally open cruise On/Off switch closes with a switch activation, the
cruise control modules detects a high voltage on the signal circuit. The cruise
control module activates the cruise control system.The set/coast switch and the
resume/accel switch will not operate the system when the cruise control module has
not activated the system based on the cruise control on/off switch signal circuit
.
The cruise control module monitors the cruise control set/coast switch in order
to determine when to capture and maintain the vehicle speed. The cruise control
module monitors the vehicle speed signal circuit in order to determine the desired
speed. The PCM pulses the vehicle speed signal circuit at 4000 pulses per minute.
After an initial set speed has been established, the cruise control module also
uses the cruise control set/coast switch signal circuit in order to tap down the
set speed when the cruise control module detects a switch activation.
The cruise control module monitors the cruise control resume/accel switch signal
circuit in order to determine when to resume the previous set speed. This feature
only works within the same ignition cycle and as long as the cruise wasn't turned
off using the cruise control On/Off switch since the last cruise engagement. After
the set speed has been resumed, the cruise control module also uses the cruise control
resume/accel switch signal circuit in order to tap up the set speed when the cruise
control module detects a switch activation.
The cruise control module assembly has a controller and an electric stepper
motor to vary the throttle in each different cruise control mode. Two components
in the module assembly help to do this. The electronic controller and the electric
stepper motor. The controller monitors vehicle speed and operates the stepper motor.
The stepper motor operates in response to the controller, to maintain the desired
cruise speed. The electric stepper motor moves a strap that is attached to the cruise
control cable which moves the throttle linkage.
Cruise Control Engaged
The cruise control module grounds the cruise engaged signal circuit when cruise
control is engaged. The PCM monitors the cruise engaged signal circuit in order
to determine when the cruise control is engaged. The PCM sends a class 2
message indicating that the cruise control is engaged to the instrument panel cluster
(IPC ) (Buick Only). The IPC illuminates the cruise indicator. The cruise control
module, cruise cancel signal circuit, is a circuit used by the PCM to inhibit cruise
control when conditions inconsistent with cruise operation are present.
Cruise Control Disengaged
The cruise control release switch and stoplamp switch are used to disengage
the cruise control. A release switch assembly and a stoplamp switch assembly are
mounted on the brake pedal bracket . To disengage the system the driver presses
the brake pedal. The speed of the vehicle at brake actuation will be stored in
the memory of the cruise module. The cruise control module uses that stored speed
when the cruise control system operation is resumed.
Cruise Control Inhibited
The PCM determines when the vehicle operating conditions are not appropriate
for cruise control operation. The PCM inhibits the cruise control operation when
any of the following conditions occur:
| • | The vehicle speed is less than 40 km/h (25 mph). |
| • | The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear. |
| • | The engine RPM is high with fuel cut-off. |
| • | The vehicle speed is too high. |
| • | The battery is either overcharged or undercharged. |
| • | The antilock brake system/traction control system is active for more
than 2 seconds |
When any of the conditions listed above are present, the PCM removes the ground
from the cruise control inhibit signal circuit. The cruise control module monitors
the cruise control inhibit circuit in order to disable the system. The PCM compares
the status of the cruise control inhibit signal circuit to the status of the cruise
control engaged signal circuit. If the cruise control engaged signal circuit indicates
that the cruise control module has cruise control engaged while the the PCM is inhibiting
cruise control operation, the PCM sets a DTC. The PCM also sends a class 2 message
indicating that the cruise control is engaged to the IPC indicator, (if equipped).
Another feature, internal to the cruise control module is the lash learn feature.
The cruise control module has the ability to learn and electronically compensate
for up to 4mm of lash in the non-adjustable cruise control cable. The cruise control
module maintains this adjustment and updates this information every 30 seconds.
