Cruise Control Description and Operation L61
Cruise Control System Overview
The cruise control system is used to control vehicle speed to a user-selected
value and an accuracy of +/- 2 km/h (1 mph) on a flat level road
(+/- 2 percent grade). The cruise control can be set at speeds at or
above 39 km/h (24 mph) with a lowest tap down speed of 32 km/h
(20 mph).
The cruise control system consists of the following:
| • | The cruise brake switch |
| • | The cruise clutch switch (manual transaxle) |
| • | The cruise control module |
| • | The cruise control switches |
| • | The cruise control throttle cable |
Unlike other systems, this system is fully electronic and does not require vacuum
or a vacuum servomotor to control movement of the throttle. To control throttle movement,
a cruise control throttle cable connected by a cable strap from the cruise control
module pulls on the throttle cam at the throttle body. The cruise control module uses
an electronically controlled stepper motor to move the throttle cable.
A lash learn feature is utilized in the cruise control module. The module uses
electronic circuits and software to learn the amount of lash (slack) in the cruise
throttle cable eliminating the need for manual adjustments when a non-adjustable cable
is used. The cruise control module can learn up to 4 mm (0.16 in) of
lash and updates, or readjusts, every 30 seconds. Vehicles with an adjustable
cruise control throttle cable will need to be adjusted. Refer to Cruise Control Throttle Cable Adjustment
.
Cruise Control System Diagnosis
Depending on the cruise control complaint, the PCM DTCs that would affect cruise
operation mentioned in Cruise Control System Operation should be diagnosed and corrected
first. If no DTCs exist, but a cruise control system problem does, the Cruise Control
System Check chart should be the starting point. This will either locate the problem
or will refer to a chart located in this section which will aid in diagnosis.
The scan tool can be used to help diagnose an inoperative cruise control system
or other faults related to the system. The scan tool displays CRUISE ENABLED, a PCM
commanded state which allows cruise to operate. The scan tool also displays CRUISE
ENGAGED, an actual feedback which tells the PCM the cruise control module is taking
control of vehicle speed. When the cruise control module is taking control of vehicle
speed, it will supply a ground to circuit 396 and CRUISE ENGAGED on the scan
tool will display YES. The scan tool can also display the stop lamp switch status
for automatic transaxles or the cruise clutch switch status for manual transaxles
as Cruise BRAKE/CLUTCH SW.
Important: An open or short to ground in the cruise engage input circuit will not affect
cruise operation. However, a short to voltage will cause an inoperative cruise control
system. CRUISE ENGAGED on the scan tool would always read NO if a short to voltage
condition occurs. This scan tool feedback will only update with the engine running.
Important: The cruise control module will not allow cruise operation if the cruise enable
input circuit is always low. The cruise control module must detect ignition voltage
anytime the vehicle is traveling less than 32 km/h (20 mph). If the
cruise control module detects a low voltage state when vehicle speed is below 32 km/h
(20 mph), it will not engage cruise for the rest of the ignition cycle even
if the fault corrects itself.
Important: CRUISE ENABLED on the scan tool displays the PCM commanded state, not a feedback
state.
With the vehicle in park and the engine running, CRUISE ENABLED and CRUISE ENGAGED
should read NO on the scan tool. With the cruise control set, CRUISE ENABLED and CRUISE
ENGAGED should read YES. If CRUISE ENABLED still reads NO when the cruise is attempting
to be set, the PCM is not allowing cruise and that condition should be diagnosed first.
If CRUISE ENGAGED continues to read NO on the scan tool when the cruise is attempting
to be set, the cruise control module can not control vehicle speed and that condition
should be diagnosed next.
Cruise Control Description and Operation
The cruise control system is an integration of the cruise control module and
PCM. Cruise control inputs from the cruise brake, cruise clutch (manual only), cruise
on/off, cruise resume/accel, cruise set/coast, and stop lamp switch go directly to
the cruise control module. Vehicle speed is sent to the cruise control module from
the PCM. The PCM creates a square wave vehicle speed signal by pulse width modulating
circuit 817 to ground. The cruise control module monitors the voltage on circuit 817,
which it pulls up to 5 volts through resistance. The lower the vehicle speed,
the longer the pulse width modulated on-time (lower the voltage on circuit 817).
The following list is the criteria that the cruise control module must detect before
it will control vehicle speed:
| • | Must have an ignition voltage supply and ground. |
| • | Must have ignition voltage at the cruise on/off switch input. |
| • | Must have zero volts at the stop lamp switch input. |
| • | Must have detected a set/coast switch transition from zero volts to ignition
voltage and back to zero volts within 1.4 seconds when all conditions to enable
cruise have been met. |
| • | Must have zero volts at the cruise enable input when vehicle speed is
over 32 km/h (20 mph) (PCM is allowing cruise to enable). The cruise
control module must also see ignition voltage on the line when vehicle speed is under
32 km/h (20 mph). If the cruise control module does not detect this,
it will NOT allow cruise for the entire ignition cycle. |
| • | Must have a valid vehicle speed signal from the PCM at or over 39 km/h
(24 mph). |
In order for the cruise control module to allow cruise operation, it must also
have an enable input from the PCM. When conditions have been met to allow cruise operation,
the PCM will supply a ground to circuit 83, which will signal the cruise control
module that the PCM has detected all of the correct enable criteria to allow cruise.
This enable command can be viewed on the scan tool as CRUISE ENABLE. The cruise control
module will not allow cruise operation until it sees zero volts on the cruise enable
circuit. The following list is the criteria for the PCM to allow the cruise control
module to control vehicle speed:
| • | Vehicle speed must be at or over 32 km/h (20 mph). |
| • | Engine speed must be below the high RPM cutoff. |
| • | The transaxle must be in a cruise gear (D4, D3 or D2 automatic only). |
| • | The clutch pedal must be fully released. Ignition voltage must be present
at the brake/clutch switch input (manual only). |
| • | The PCM must see one valid cruise clutch switch transition from ignition
voltage to zero volts and back to ignition voltage once in the ignition cycle (manual
only). |
| • | The PCM must see one valid stop lamp switch transition from zero volts
to battery voltage and back to zero volts once in the ignition cycle (automatic only). |
| • | Vehicle acceleration or deceleration rate must be within acceptable limits. |
| • | Traction control must NOT be active. |
| • | No PCM DTCs that would affect cruise operation can be set: |
| - | Engine coolant temperature circuit |
| - | Engine coolant overtemperature |
| - | Stop lamp switch circuit |
| - | Transaxle range switch circuit |
Once the cruise control module receives correct voltage levels at the various
inputs, it will engage cruise control and supply a ground to the cruise engage circuit 396.
This lets the PCM know that the cruise control module is taking control of vehicle
speed. CRUISE ENGAGED on the scan tool will display YES when the cruise control module
is taking control of vehicle speed.
Cruise Control Description and Operation Component - L81
Stop Lamp Switch
The stop lamp switch operates the vehicle stop lamp and generates signals to
control several electronic modules on the car. The switch is a normally open switch
when the brake pedal is in its rest position. When the brake pedal is pressed, the
pressure on the stop lamp switch plunger is released, the switch is closed, and the
brake lights turn ON. If the cruise is ON at the time the brake pedal is pressed,
the stop lamp switch is closed, and the cruise will not engage.
Steering wheel theft deterrent systems can possibly cause the switch to get
over adjusted. If you notice that the customer's switch is over adjusted, fix the
adjustment, verify that the customer has used a steering wheel theft deterrent in
the vehicle, and inform the customer that the stop lamp switch can become over adjusted
when they use a steering wheel theft deterrent system.
Cruise Brake Switch
The cruise brake switch disables the cruise control function when the brake
pedal is pressed. If the vehicle has the cruise control option, then a cruise brake
switch can be found on the brake pedal. When the brake pedal is pressed, this switch
opens, and a signal is sent to the ECM to disable the cruise. The cruise brake switch
is normally closed supplying 12 volts when the ignition is ON and the brake
is OFF. A scan tool should display ON when the brake pedal is depressed and should
read OFF with the brake pedal released.
The cruise brake switch consists of battery voltage sent through a brake switch
to the ECM. When the brake is not applied, the brake circuit sends voltage to the
ECM. As the brake is depressed, and voltage is removed, the ECM will disengage the
cruise function. The cruise/brake switch acts as a redundant disable for the cruise
when the brake is applied. If the ECM detects a brake circuit fault, the cruise will
disable. If the cruise brake switch is stuck closed when the vehicle has cycled 2 times
from 0-55 km/h (0-34 mph) and vehicle speed decreases more
than 4 km/h (2.5 mph) per second, cruise will be released.
Cruise ON/OFF Switch
The cruise ON/OFF is a normally-open push-button switch that allows the driver
to engage/disengage the cruise control system. When the button is ON, the light-emitting
diode (LED) will illuminate, and voltage will be applied from the underhood fuse block
(UHFB) through the coil assembly (roll connector) to the ECM cruise ON/OFF input.
Engine Control Module (ECM)
The engine control module (ECM) is a hybrid design microprocessor based computer
that is the main component of engine control system. Included in the tasks of the
ECM is to control the cruise control system. The ECM processes switch inputs indicating
that the vehicle driver has requested cruise control. At this point, the ECM regulates
throttle angle and other factors to maintain a constant vehicle speed. The ECM also
receives inputs directly from the cruise/brake switch, and the brake switch to deactivate
cruise control, and return vehicle control to the driver.
Accelerator Pedal Position Sensor
The accelerator pedal position (APP) sensor is a part of the new electronic
throttle control system on this vehicle. There is no longer a cable linking the accelerator
pedal to the throttle butterfly. Instead, the pedal position sensor relays the desired
throttle position to the ECM. The ECM then commands the throttle motor to move the
butterfly to the desired position.
The APP system employs 2 independent potentiometers. One is redundant,
and exists to diagnose the first, and also to serve as a temporary back-up in case
the first potentiometer fails. When the accelerator pedal is at its normal resting
state, both of the potentiometers read a low value. Under wide-open-throttle (WOT),
both of the potentiometers read a high value. It is important to note that the voltage
on the signal wire of potentiometer 2 should always read half the value of
the voltage on the signal wire of potentiometer 1.
This sensor communicates a desired vehicle speed to the ECM when cruise control
is requested by the driver.
Throttle Position (TP) Sensor
The throttle position (TP) sensor is mounted on the throttle body assembly.
The sensor is comprised of 2 potentiometers with common supply and ground circuits,
and independent signal circuits. As the throttle opens, the signal wire on sensor 1
reads a higher voltage, and the voltage on signal wire for sensor 2 decreases.
This is used as a feedback device to allow the ECM to compare the throttle body's
present location to where it is commanded to be.
This sensor is also used with the throttle motor to correctly position the throttle
butterfly to maintain the vehicle speed commanded by the cruise control input. An
error with the TPS system will disable cruise operation.
Cruise Control Description and Operation System - L81
Cruise Control System Overview
The cruise control system is used to control vehicle speed to a user-selected
value and an accuracy of +/- 2 km/h (1 mph) on a flat level road
(+/- 2 percent grade). The cruise control can be set at speeds at or
above 39 km/h (24 mph) with a lowest tap down speed of 32 km/h
(20 mph). The cruise control system consists of the following:
| • | The cruise brake switch |
| • | The cruise control switches |
Unlike other systems, this system is fully electronic and does not require vacuum
or a vacuum servomotor to control movement of the throttle plate. To control throttle
movement, the ECM will electrically control the throttle plate during cruise control
mode as well as during all other engine running conditions.
Cruise Control Description and Operation
The cruise control system is an integration of the cruise control switches,
brake switches, and ECM. Cruise control inputs from the cruise brake switch, cruise
ON/OFF switch, cruise RESUME/ACCEL switch, cruse SET/COAST switch, and stop lamp switch
go directly to the ECM. The following list is the criteria that the ECM must detect
before it will control vehicle speed:
| • | Must have ignition voltage at the cruise ON/OFF switch. |
| • | Must have ignition voltage at the cruise brake switch input. |
| • | Must have zero volts at the stop lamp switch input. |
| • | Must have a valid vehicle speed signal from the TCM over the CAN link
at or over 39 km/h (24 mph). |
| • | No DTCs must be present that would interfere with the ability to control
the throttle plate correctly or would interfere with the ability of the driver to
disengage the cruise control under any circumstance. These would include any APP senor,
brake switch, serial data communication, ECT sensor, system voltage, TP sensor, throttle
actuator, transaxle range switch, or vehicle speed circuit. |
| • | Must have detected a SET/COAST switch transition from zero volts to ignition
voltage and back to zero volts within 0.06-1.4 seconds when all conditions
to enable the cruise have been met. |
Once the ECM receives the correct voltage levels at the various inputs and the
other criteria has been met, it will engage cruise control. The ECM will not disengage
cruise control unless:
| • | A brake transition is detected. |
| • | Transmission is placed in a non-cruise gear (P, R, or N). |
| • | Vehicle speed drops below 32 km/h (20 mph). |
| • | Vehicle speed exceeds 161 km/h (100 mph). |
| • | The vehicle is accelerating or decelerating too quickly. |
| • | The traction control is active. |
| • | The engine coolant temperature is too high. |
| • | Any of the DTCs mentioned above have set or a fault is detected in any
of those circuits. |
Cruise Control System Diagnosis
Depending on the cruise control complaint, the ECM DTCs that would affect cruise
operation mentioned in Cruise Control Description and Operation should be diagnosed
and corrected first. If no DTCs exist, but a cruise control system problem does, the
Cruise Control System Check chart should be the starting point. This will either locate
the problem or will refer to a chart located in this section which will aid in diagnosis.
The scan tool can be used to help diagnose an inoperative cruise control system
or other faults related to the system. The scan tool displays CRUISE SWITCH, CRUISE
SET/COAST, and CRUISE RESUME/ACCEL inputs for the cruise control switch states. The
scan tool also displays BRAKE SWITCH (stop lamp switch) and CRUISE BRAKE SWITCH states.
Cycling these switches while monitoring each parameter may lead to the cause of an
intermittent cruise control condition.
