Diagnostic Doctor 16 The Diagnostic Doctor tackles body control modules In our new series, the Diagnostic Doctor, Aftermarket Magazine is focusing on real-world technical problems brought to our readers by their customers. Below, we look at an issue in which a customer with a 2017 Ford Fiesta complained that their driver’s-side front window wasn’t working, and we walk through the diagnostic steps needed to identify the cause. Further detail and background on the topic can be found in a more in-depth article on the Aftermarket website at tinyurl.com/DD0626, where you can also submit your own diagnostic dilemmas to the Diagnostic Doctor, which we will review for potential inclusion in future editions of Aftermarket Magazine. Acustomer with a 2017 Ford Fiesta comes into the workshop complaining that their driver’sside front window isn’t working. At first glance, this could involve a failed motor, a faulty switch, wiring damage or a module failure. Traditional diagnosis might involve removing trim panels and chasing wiring – a time-consuming process with no guarantee of a quick answer. However, on newer vehicles that use body control modules, complex diagnosis starts with understanding inputs, outputs and data flow rather than chasing wires. In these cases, a diagnostic scanning tool is necessary. So, with our Snap-on Triton Gen 3 scan tool connected, step one should be a pre-scan of the vehicle. In this example, no diagnostic trouble codes were present. So next, we accessed the driver’s door module on the scan tool, and step two is to use functional tests. We navigated to: Functional Tests > Actuator tests > Front window down output. From here, the window motor can be commanded ON or OFF directly from the scan tool. To simplify analysis, we used the ‘Custom Data List’ feature, deselected all parameters and selected only ‘Drivers window up’ switch and ‘Drivers front window switch – Drivers door’. Returning to the list view,
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