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BY Frank Massey I think it is very easy, with the fast pace of technology, to focus on the present while forgetting the lessons of the past. With that in mind, I’m going to take a review of current measurement and its application, past, present and future. My interest in current measurement goes back to the 1980s, when control systems were very simple when compared to the present day. They did however have similar responsibilities. I was already using oscilloscopes for our diagnostic tests as serial diagnostics were in their infancy. Our focus was on wave form profile and event synchronisation, for example cam, crank sensors, injector and ignition events. This proved to be a successful process. I will explain why a little later. As our reputation increased, we attracted more trade work. As is the case today, blame was often directed towards the PCM. As our trade customers were often reluctant to bring the complete vehicle to us, we became involved in off-car PCM testing. This was an automated function test of the PCM’s ability to control actuators. We quickly became aware of false pass and fail results which, when tested on the problematic vehicle, proved to be current flow-related. This raised our interest and concern, and we realised that a suitable in-situ test process needed to be found. In those days, all our electronic test tools came from the electronics sector as no satisfactory test tools were available within 20 AFTERMARKET NOVEMBER 2021 TECHNICAL www.aftermarketonline.net CURRENT MEASUREMENT, PAST, PRESENT AND FUTURE Oscilloscopes at the ready everyone, as in this issue Frank is looking at current measurement the motor industry, unlike today. We were directed to the hall effect current clamps so common within the PICO and other range of test kits. Importance To qualify the importance of the process, I will explain a very interesting fault from way back in the early 1990s.The vehicle; A BMW 850 V12 which employed two synchronised PCMs, each controlling one bank. The car came to us running on one bank with one ignition coil completely burned out due to excessive current flow. We carefully checked the wiring for shorts, ordered a genuine new coil, swapped the PCM over to the faulty bank and successfully ran the vehicle on that bank. We then sent the PCM off for repair. When refitting to the vehicle, we observed it run on all cylinders for 5-10 seconds before burning out the other coil. Why was this? To condense quite a lengthy story, it transpired that the original faulty PCM allowed a current runaway within the coil primary circuit which did not show up under off-car bench simulation. This was the exact problem encountered with the network 500. By this time, all our off-car testing had ceased in favour of event and current path analysis using a scope with the vehicle intact. Intervention I have recently covered current flow in the ignition primary circuit (please refer to my two-part series in the Fig.1