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www.aftermarketonline.net NOVEMBER 2021 AFTERMARKET 27 Test plan The main power supplies were from several fuses in the engine bay fuse box, most of which were fed power when the engine control relay was energised. This also then turned on the fuel pump relay and allowed the low- pressure fuel pump in the tank to operate. I now had information to write up a test plan. My plan was to check low fuel pressure as it was easily done by a Schrader valve on the top of the engine. If there was nothing I could now be confident to test the fuses for power and the engine control relay and the fuel pump relay for correct operation as these items linked all my faults together. Upon connecting a gauge to the fuel system and turning on the ignition, I had no fuel pressure coming from the tank, so I was happy to now test at the fuse box. I checked the fuses which were supplied power from the engine control relay and all had nothing, so I moved onto the engine control relay. Upon touching the relay to remove it to test its inputs, a click was heard and the engine started to buzz indicating there was power being supplied to components. A quick circuit check showed the relay to be faulty and intermittently latching correctly internally so a new relay was fitted and the system retested. I now had power at all the fuses required and the low fuel pressure was now correct as the in tank pump was being energised. Looking to Fig.3, a check of live data now showed the correct voltages. A fault code clear was then done and upon cranking the engine it now fired into life, with only the EGR fault code remaining. After some checks this was found to be seized. The vehicle was then rebuilt and handed back to the customer. Starting fresh To summarise, a faulty relay caused all the problems. Having seen similar fault codes on the previous vehicle I mentioned, it would have been very easy to go down the same path. However, starting fresh and applying methodical thinking and a plan of action with technical information found the fault quickly and accurately. Always confirm the cause of the problem and don’t rely on what you have seen before as it may not always be the same. Right: Fig 3. PASSION FOR TECHNOLOGY. EMISSION CONTROL COMPONENTS FOR EMISSION CONTROL FROM PIERBURG – FOR CLEAN AIR AND THE ENVIRONMENT www.ms-motorservice.com/emission-control