Aftermarket December/January 2023

I ntermittent faults are always the most difficult to find. Therefore, when I was tasked with attempting to diagnose and rectify an intermittent cutting-out fault I knew it would not be straightforward. The customer had heard of me via my social media page and local garages who use me for their diagnostic work. The customer complained that the vehicle, a Renault Traffic 2.0L TDI, would stall on its own, intermittently. The vehicle would then start up again as soon as the ignition switch had been cycled. This fault could occur within the hour or take five hours before it would surface again. The customer advised there was no rhythm or rhyme to the fault, and it could occur at any time. Knowing this would be a very time-consuming fault I advised the customer I would need the vehicle for a week to ensure experiencing the fault and carrying out testing thoroughly. The customer was more than happy to oblige, as long as I fixed the fault, so no- pressure then… Initial approach I started by carrying out a full system scan of all the vehicle’s computers. I found in the engine control module a fault code for ‘Computer internal electronic fault.’ Please refer to Fig.1. This was a good starting point as this fault code is very specific and often is caused by an internal control module error, wiring fault to the computer or a component directly related to the computer. However, at the cost of a new engine computer (over £1,200) I needed to pinpoint the fault and not rely solely on the fault code provided. I cleared all the fault codes present in the engine ECU and ran the vehicle in the workshop until it cut out. Once the vehicle cut out, I re-read all the fault codes and the only code which returned was the internal electronic fault as described earlier. I noticed that when the vehicle had stalled, communication was still present and live data parameters were still being displayed by the scan tool. This indicated the engine computer is alive and operating. This was a good indicator that the engine computer is receiving the voltage and ground supply. Without it, communication would not be possible. I needed to confirm this for certain as I cannot diagnose a fault solely on suspicion. To access the engine ECU on this vehicle I needed to remove the bumper, headlight, and security cage around the engine ECU. Before I attempted to remove all those components, as this was very time-consuming, I wanted to use an oscilloscope to check the fuses that feed the engine ECU at the time of the stall. These fuses are on the output 26 AFTERMARKET DECEMBER/JANUARY 2023 TECHNICAL www.aftermarketonline.net IS IT THERE OR NOT? How long does it truly take to find an intermittent fault, and how do you manage to isolate it? BY Ryan Colley, Elite Automotive Diagnostics Fig.1 Fig.2 stage of the engine control relay, therefore if it was the relay that was failing, for whatever reason, I would see the drop-out on the oscilloscope. As you can see from Fig.2, the supplied voltage and ground were constant and did not drop-out. This indicated that the engine control relay was latched and doing its job properly when the fault was present. I now had no choice but to access the engine computer to carry out further testing. By removing the bumper, headlight, and security cage I was able to access the engine computer and its respective wiring harness. Concerned still of a voltage or ground supply issue, I connected the oscilloscope to the engine computer supplies and verified, during the stall, that these were present. Next, I wanted to verify the main inputs and outputs of the computer that could contribute to a stalling condition. I connected to the camshaft and crankshaft position sensor wiring, directly at the engine computer. I also connected to the injector wire using an amp clamp to determine if injector operation remained constant during