Your best bet , take it to a qualified repair shop . You have no idea how complex this is ?
Having a scan tool hooked up to check for DTC'S - diagnostic trouble codes should be the first step in the diagnostic procedure .
Powertrain Control Module (PCM) Diagnostic Trouble Code (DTC) Index
DTCs
Description
Source
Action
P0500
Vehicle Speed Error
PCM
REFER to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.
P0579
Cruise Control Multifunction Input A Circuit Range/Performance
PCM
Go To Pinpoint Test C .
P0581
Cruise Control Multifunction Circuit High
PCM
Go To Pinpoint Test C .
P0833
Clutch Pedal Switch B Circuit
PCM
Go To Pinpoint Test D .
P1572
Brake Pedal Switch Circuit
PCM
Go To Pinpoint Test B .
P1703
Brake Switch Out of Self-Test Range
PCM
Go To Pinpoint Test B .
All other DTCs
-
PCM
REFER to the Powertrain Control/Emissions Diagnosis (PC/ED) manual to continue diagnosis.
Then reading up on how it works should be done .
Principles of Operation
The speed control system is controlled by the powertrain control module (PCM). The speed control system is designed to maintain a selected vehicle speed between 48 and 200 km/h (30 and 124 mph). The speed control system is controlled by the steering wheel mounted switches (ON, OFF, SET+, SET-, and RESUME), the stoplamp switch, clutch pedal speed control deactivator switch (manual transmission), and the speed control deactivator switch. The steering wheel mounted switches are hardwired to the PCM through the clockspring.
The speed control functions include:
- turning the speed control system on.
- setting and maintaining the desired vehicle speed.
- accelerating the vehicle speed.
- decelerating the vehicle speed.
- turning the vehicle speed control system off.
- cancelling the speed control.
Pressing and releasing the ON switch turns the speed control system on. Pressing and releasing the SET+ or SET- switch while the vehicle is traveling at the desired speed activates the speed control system.
Tapping the SET+ or the SET- switch while in the set mode increases or decreases the maintained vehicle speed by 1.6 km/h (1 mph) per tap, respectively. If either button is pressed and held, the vehicle speed continues to accelerate (SET+) or decelerate (SET-) until the button is released.
Pressing and releasing the OFF switch, or switching the ignition switch to the OFF position, turns the speed control system off. Applying the brake pedal puts the speed control system into the standby mode. Pressing the RESUME button when the speed control system is in the standby mode causes the vehicle to accelerate to the last set speed. RESUME does not function if the OFF button is pressed or if the current vehicle speed is below the minimum operational speed.
The clutch pedal speed control deactivator switch is used on vehicles equipped with a manual transmission. When the clutch pedal is applied with the vehicle speed control system engaged, the normally closed switch opens and signals the PCM to deactivate the speed control.
The speed control deactivator switch is provided as an additional safety feature. When the brake pedal is applied, an electrical signal from the stoplamp switch is sent to the smart junction box (SJB), which then sends a message to the PCM to deactivate the speed control system. Under increased brake pedal effort, the speed control deactivator switch opens and removes the voltage signal from the PCM input circuit, deactivating the speed control system.
Whenever the speed control system is engaged and active, a speed control icon on the instrument cluster is illuminated.
The inputs to the PCM are:
- Output shaft speed (OSS) sensor
- Transmission range (TR) sensor
- Speed control switch
- Clutch pedal speed control deactivator switch
- Speed control deactivator switch
- Accelerator pedal position sensor
- SJB
- Parking brake
The outputs of the PCM for the speed control system are:
- Speed control indicator lamp
- Throttle command
The speed control system throttle position is completely controlled by the PCM through the electronically controlled throttle body. Speed control electronics are contained entirely within the PCM.
When the speed control system is active, the PCM corrects for deviations in the actual vehicle speed by proportionally moving the throttle plate. The PCM modulates the throttle to minimize error between actual, and desired, vehicle speed.
The PCM strategy uses the throttle control for smooth accelerations.
The PCM sends a message over the controller area network (CAN) to the instrument cluster whenever the speed control telltale should be turned on or off.
In the event of an OFF command or a deactivation request from any source, the speed control system carries out a deactivation and immediately returns the throttle to the idle position.
The speed control system provides self-diagnostics. The speed control is disabled anytime an error is detected in the system. No cluster telltale or message center messages are displayed when faults occur. Fault codes are logged by the PCM.
An electronically controlled throttle system fault also causes the speed control system to be disabled and a warning telltale (wrench light) or a message center message is displayed.
Additionally, the following conditions cause the speed control system to deactivate:
- Transmission gear selector in a position other than D or OD (automatic transmission)
- Vehicle clutch pedal is applied
- Speed control set speed is over-ridden with the accelerator pedal for a period longer than 5 minutes
- Vehicle speed loss from set speed of greater than 16 km/h (10 mph) occurs
- Vehicle speed falls below the minimum allowable limit of 48 km/h (30 mph)
- Parking brake is applied
- Speed control switch is pressed or stuck for longer than 2 minutes
Inspection and Verification
- Verify the customer concern.
- Visually inspect the following for obvious signs of mechanical or electrical damage.
Visual Inspection Chart
Mechanical
Electrical
- Smart junction box (SJB) fuse 18 (10A)
- Circuitry
- Speed control switch
- Clutch pedal speed control deactivator switch
- Speed control deactivator switch
- Stoplamp switch
- Powertrain control module (PCM)
- If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
- Verify the speedometer operates correctly without speed control by test driving the vehicle. If the speedometer does not operate correctly, refer to Section 413-01 .
- Verify the stoplamps operate correctly with the ignition switch in the ON position. If the stoplamps do not operate correctly, refer to Section 417-01 .
- Verify the parking brake warning indicator is operating correctly. If the parking brake warning indicator does not operate correctly, refer to Section 413-01 .
- If the cause is not visually evident, connect the diagnostic tool to the data link connector (DLC) and select the vehicle to be tested from the diagnostic tool menu. If the diagnostic tool does not communicate with the vehicle:
- check that the program card is correctly installed.
- check the connections to the vehicle.
- check the ignition switch position.
- If the diagnostic tool still does not communicate with the vehicle, refer to the diagnostic tool operating manual.
- Carry out the diagnostic tool data link test. If the diagnostic tool responds with:
- CAN circuits fault; all electronic control units no response/not equipped, refer to Section 418-00 .
- No response/not equipped for PCM, refer to Section 418-00 .
- System passed, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs, and carry out the self-test diagnostics for the PCM.
- If the DTCs retrieved are related to the concern, go to the Powertrain Control Module (PCM) Diagnostic Trouble Code (DTC) Index.
- If no DTCs related to the concern are retrieved, GO to Symptom Chart .