Home » GM 6.5 » GM/Detroit 6.5L ENGINE CONTROLS – Cruise Control Diagnosis

GM/Detroit 6.5L ENGINE CONTROLS – Cruise Control Diagnosis

Circuit Description
The cruise control multi function lever is wired directly to the PCM. The cruise on/off, set/coast and resume/accel signals are inputs to the fuel control portion of the PCM. These inputs allow the PCM to control and hold a requested speed. The cruise can be disengaged at any time by applying the brakes. This input is sent to the PCM by the cruise control brake switch.

Diagnostic Aids
If the cruise is inoperative, and no cruise control or brake switch DTCs are stored, check for the following conditions:
• A malfunctioning cruise multi function switch/ wiring harness (opens or ma lfunctioning connections).
• The clutch pedal switch is stuck in the open position.

Other conditions that will not allow the cruise control to engage that do not pertain to the cruise system.
• The vehicle speed is below 25 MPH (if the cruise control is already set, the cruise will disengage at 20 MPH).
• The vehicle is in 4 wheel drive low.
• Any DTC that puts the vehicle in Back Up Fuel Mode (Back Up Fuel Mode affects the fuel control portion of the PCM). Refer to the appropriate DTC.
• More than one accelerator pedal position (APP) DTC is set.

Test Description
Number(s) below refer to step number(s) on the Diagnostic Table.
3. This step checks for ignition voltage to the cruise control switch.


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