BY Frank Massey Most of the problems I encounter in my current role are of a simple nature and are often solved with a scan tool or a digital multi meter (DMM). I should point out that the DMM I use is an extremely high-spec example. However, most of the tests I rely on can be conducted with a much more basic tool. An interesting problem arrived in the guise of a Skoda Fabia 1.2 tsi. The vehicle was known to me due to a previous repair to the driver’s window module (J386). On that occasion, a broken power supply in the A post loom was responsible. I should add the passenger window was also faulty, but the owner did not authorise further work. More on this story later. On this occasion the vehicle was towed in as a nonrunner. As often happens, preliminary tests and swap outs had been carried out on my two days off. So, Tuesday AM at the handover it was explained that there was no fuel pump operation, and a new genuine pump had been fitted, without effect. Plan I attached our TOPDON scan tool and conducted a global system scan. My attention was drawn to an absence of the 28 AFTERMARKET OCTOBER 2023 TECHNICAL www.aftermarketonline.net A MONTH IN THE LIFE OF A VEHICLE TECHNICIAN Frank gets tangled up in a Skoda Fabia wiring conundrum, and he finds that when one door closes, a window opens… PCM on the HC CAN network. This directed me to scope the network and check at the PCM and power control module. The network was good, with correct voltage 1.5/2.5 and 2.5/3.5 with clean transition (rise time). So, this was my plan; Simplistically a PCM requires, power, ground, triggers, and outputs to ignition, injectors, and fuel pump to stand a chance of running the engine. Now reverse that logic - Why? It quickly establishes what is missing. We knew the fuel pump was not working, and due to excellent engine access, we quickly established no outputs. It was starting to look like terminal PCM failure. At this point we informed the owner of cost. Despite the vehicle being in excellent condition, he indicated his wish to scrap the vehicle. We offered to purchase the vehicle at scrap valuation of £250 with an online purchase valuation of £2,500. So, we now own the vehicle with no concern for diagnostic or repair cost. Simple path Following my logic plan, I progressed on to check the power and grounds to the PCM. Taking a simple path, which I guarantee will get more complicated later, I began checking the fuse panel in the offside dash panel. Using the fuse guide sticker, I quickly established no voltage at Part seven Fig. 1
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