A vehicle is experiencing intermittent cruise control functionality. A review of the wiring diagram shows the cruise control module receives inputs from the brake pedal position (BPP) sensor and the vehicle speed sensor (VSS). Which of the following is the most effective initial diagnostic step to narrow down the potential cause?
- AConnect a scan tool and monitor live data for BPP sensor and VSS readings.
- BPerform a resistance check on the cruise control switch.
- CInspect the cruise control module for physical damage.
- DCheck for continuity of the cruise control module power and ground circuits.
Show answer & explanationAnswer & explanation
Correct answer: A. Connect a scan tool and monitor live data for BPP sensor and VSS readings.
Since the cruise control module relies on accurate input from the BPP and VSS, monitoring their live data with a scan tool is the most effective initial step. This allows the technician to immediately see if these critical inputs are present and accurate, especially when the intermittent fault occurs. If the inputs are correct, the issue lies elsewhere; if they are erratic or missing, the problem is likely with one of those sensors or their circuits.
Why the other options are wrong
- B. A resistance check on the cruise control switch is a static test and might not reveal an intermittent issue. Furthermore, the question highlights BPP and VSS as key inputs.
- C. Inspecting for physical damage is a visual check and less likely to reveal an intermittent electronic issue with inputs.
- D. While power and ground are essential, checking them first doesn't address the specific input dependencies of the cruise control that are explicitly mentioned as critical.
Live Data (Scan Tool)
Real-time display of sensor inputs, actuator outputs, and calculated values from vehicle control modules, used to observe system operation and diagnose intermittent faults.
- Displays data in real-time.
- Useful for dynamic diagnosis.
- Helps identify faulty sensors/actuators.
Memory trick: To see what the module 'sees', watch its live data stream.