Diagnostic Aids

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

The cruise control system can be inhibited or disengaged for a number of reasons. These reasons may be a normal function of the vehicle or as a result of action the driver has taken. The cruise control system may also be inhibited or disengaged because of a fault in a vehicle system. The K20 Engine Control Module has a scan tool data list available that can help identify what may have caused a cruise control inhibit or disengage. The scan tool ECM Cruise Control Disable History Data list identifies conditions that will inhibit cruise control. When the cruise control system is inhibited the cruise control system will be prevented from engaging when requested by the driver, or the cruise control system will disengage, if the driver was actively utilizing the system.

When attempting to diagnose the system, it is important to discuss with the customer the conditions under which the apparent malfunction occurred. This is critical to help identify those scenarios where the inhibit or disengage is the result of a driver action or normal system response and clarify how the function works. It is also critical to identify when the apparent malfunction occurred when attempting to replicate the condition. The parameters in the scan tool ECM Cruise Control Disable History Data list can be used to help isolate what is causing an inhibit or disengage condition. The scan tool ECM Cruise Control Disable History Data list has parameters that identify the last eight causes of an inhibit and the last eight causes of a disengage. For each Cruise Control Inhibit History and Cruise Control Disengage History parameter, extra information is included in additional parameters: Odometer at First Malfunction, Odometer at Last Malfunction, Diagnostic Status, Malfunction Counter, and Ignition Cycles Since Last Diagnostic Event. The scan tool parameters are a rolling snapshot of the last eight inhibit and disengage reasons, however, if the same condition causes an inhibit or disengage, the reason will not be logged in the next parameter. Instead, the Malfunction Counter parameter will increment and the Odometer at Last Malfunction parameter will update with the most recent odometer value that the condition occurred. When diagnosing an inhibit or disengage concern, especially in the case of an intermittent condition, these parameters are useful in helping determine the cause. Recurring causes will have a larger number in the Malfunction Counter parameter and will likely have a wide variance between the Odometer at First Malfunction and Odometer at Last Malfunction value, indicating the condition has occurred over a period of time driving the vehicle.