Chart C-17 Cruise Control Diagnosis (Functional Check)

Chart C-17cruise Control Diagnosis:

Cruise Control Schematic:

CIRCUIT DESCRIPTION
The stepper motor cruise module communicates with the Powertrain Control Module (PCM) over three lines (cruise engaged, cruise disabled and Vehicle speed Sensor (VSS) output). The cruise enable status tells the PCM if the cruise control system is enabled. VSS output is the speed signal from the vehicle speed sensor through the PCM to the cruise control module. The cruise disable line allows the PCM to disable cruise under the various conditions described below:

^ Engine not running.
^ Transmission out of gear (manual trans.).
^ Diagnostic Trouble Code (DTC)(s) 19, 53 or 65 is present
^ Safety fuel cut-off is active.
^ Transmission in park or neutral (auto trans.).

If the PCM detects any one of the above conditions, it will interrupt the ground at the cruise disable signal (CKT 83) to request that cruise control be disabled.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. The vehicle must be driven in the enabling criteria listed above in order for the PCM to allow cruise to be enabled. When the vehicle is out of this criteria, the Tech 1 will read stepper cruise "Disabled".
2. The cruise speed set has to be above the minimum speed required for cruise operation. Be sure to drive in an area where enough room is allowed for cruising.
3. 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. Circuit 83 provides a ground to the cruise control module. This step checks for an open or shorted cruise disable circuit.
4. At this point, 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 fault is in the cruise control module or is a throttle linkage problem.
5. 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 fault is an open or shorted cruise engaged circuit or a cruise control module.


DIAGNOSTIC AIDS
An "Intermittent" problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.

Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.

Check for:

Poor connection or damaged harness
Inspect PCM harness for open or short to ground in CKT 83, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connections, and damaged harness.