05 Mar 2024

Is it there or not?

Intermittent 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 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 the stall event. If not, I could then determine if injector pulse ceased due to a loss of a cam or crank sensor signal.
As you can see from Fig.3, the cam and crank sensor signals remained and the injector control was the first to be lost, thus resulting in a stall of the engine. The engine computer was no longer providing injector control to keep the engine running. Since proper cam position signal remained during the stall it was unlikely to be a 5v reference fault, as the 5v reference is used to power the camshaft sensor. At this point, from the evidence I had retrieved coupled with the fault code I initially found, I was highly suspicious of an internal engine computer fault.

There are no problems, only solutions
Due to the current issues surrounding the supply of electronic parts in the UK I was not able to obtain an engine control module directly from the dealership. I had only one option which was to locate a used control unit and carry out cloning of the original control module.

This process requires removal of the engine computer from the vehicle and connecting a programmer directly to the ECU. Please refer to Fig.4. You are then required to read the flash and the EEPROM internal to the computer and transfer that data from the suspect’s faulty original ECU into the donor ECU. Please refer to Fig.5 and Fig.6.
By going through this process, you are effectively making an exact copy of the original ECU, allowing all the immobiliser and coding data to be transferred so you can simply connect the ECU back to the vehicle without any further programming being required. This will only rectify a hardware-related fault. If there was a software-related issue, then you will effectively copy the fault onto the donor unit. I was confident this was a hardware-related issue rather than a software-related problem. Once I had cloned the ECU, I left the engine idling to attempt to re-create the original complaint. I can confirm the donor ECU I cloned had fixed this intermittent fault as the stalling no longer occurred.
With intermittent faults, the best way to tackle them is to gather as much data as you possibly can, performing as little work as possible. This will then stop the hours and hours of stripping parts off needlessly to carry out inspections that are not required. A solid foundational knowledge of how systems operate on today’s complex vehicles also provides a strong advantage. Logic can then be used to narrow down the possibilities that could cause the fault as we have done in this diagnosis and repair.