Refer to
VSS and Cruise Control
schematic.
Diagnosis
The following table will diagnose the Cruise Disable and Cruise Engaged circuits. Refer to the Electrcial Diagnosis portion of the service manual when diagnosing the remaining cruise control system circuits.
Circuit Description
The stepper motor cruise module communicates with the PCM over three circuits (cruise engaged, cruise disabled and VSS output). The cruise enable status tells the PCM if the cruise control system is enabled. The VSS output is the speed signal from the vehicle speed sensor through the PCM and used by the cruise control module. The cruise disable line allows the PCM to disable cruise under the various conditions described below:
| • | Engine is not running. |
| • | Transmission is in park, neutral or reverse (auto trans.). |
| • | Transmission is out of gear (manual trans.). |
| • | Safety fuel cut-off is active. |
| • | If the PCM detects any one of the above conditions, it will interrupt the ground at the cruise disable input circuit and disable the cruise control. |
Diagnostic Aids
| • | This table will not diagnose any other cruise control system circuits other than those connected to the PCM. For diagnosis of the remaining circuits, refer to the Electrcial Diagnosis portion of the service manual for cruise control diagnosis. |
| • | An Intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation. |
| • | The cruise control system may disable if actual speed is less than 15 mph (24 km/h) than commanded vehicle speed; i.e. towing a trailer, or climbing a steep grade. |
| • | Minimum vehicle speed for setting the cruise control system is 25 mph (40 km/h). |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
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The A Powertrain On Board Diagnostic (OBD) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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The vehicle must be driven in the enabling criteria listed above in order for the PCM to allow the cruise control to be enabled. When the vehicle is out of this criteria, the scan tool will read stepper cruise Disabled.
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The cruise speed set has to be above the minimum speed (25 mph/40 km/h) required for cruise operation. Drive vehicle in an area where enough room is allowed for cruising.
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If the vehicle was in the enabling criteria for cruise operation, the PCM should have read stepper cruise Enabled even if cruise was not requested. CKT 83 provides a ground to the cruise control module. This step checks for an open or shorted cruise disable circuit.
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The PCM is allowing cruise operation and the cruise module is telling the PCM that the cruise is engaged. If the vehicle will not maintain the set speed, then the malfunction is in the cruise control module or is a throttle linkage problem.
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Even though the cruise module can maintain the set speed, the cruise control module may not tell the PCM that it is controlling vehicle speed. This step determines if the malfunction is an open cruise engaged circuit or a malfunctioning cruise control module.
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The PCM senses if the cruise control module is controlling the vehicle speed by applying 12V on the cruise engage circuit displays Yes on a scan tool when the cruise control module grounds the circuit. A cruise engaged circuit that is shorted to ground will always display Cruise Engaged asYes on the scan tool.
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The replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to PCM Replacement/Programming and to the CKP System Variation Learn Procedure .
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If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No |
Was the A Powertrain On Board Diagnostic (OBD) System Check performed? | -- | Go to A Powertrain On Board Diagnostic (OBD) System Check | ||
Does the scan tool display Cruise Enabled? | -- | |||
Set the cruise control to the current speed. Does the scan tool display Cruise Engaged as Yes? | -- | |||
Does the test light illuminate? | -- | |||
Does the cruise control system maintain the set speed? | -- | Go to Cruise Diagnosis | ||
6 | Does the cruise control system maintain the set speed? | -- | Go to Cruise Diagnosis | |
7 | Repair the short to battery positive voltage in the cruise disable circuit. Is the action complete? | -- | -- | |
8 | Check the cruise disable circuit for a poor connection or an open and repair as necessary? Was a repair necessary? | -- | ||
Depress the brake pedal enough to disable the cruise control system. Does the scan tool display Cruise Engaged as NO? | -- | |||
10 | Check the cruise engage circuit for a poor connection or an open and repair as necessary. Was a repair necessary? | -- | ||
11 | Repair the short to ground in the cruise engage circuit. Is the action complete? | -- | -- | |
Replace the PCM. Refer to PCM Replacement/Programming . Is the action complete? | -- | -- | ||
Operate vehicle within the conditions under which the original symptom was noted. Does the system now operate properly? | -- | System OK, Refer to Diagnostic Aids |
