Ok, after allowing the vehicle to stand for a good hour I establish that the current flow doesn’t drop below 340 mA. Different makes and models display a variety of shutdown characteristics and plenty of time must be given to allow full sleep. I now set about pulling the fuses one at a time, until I identify which circuit is responsible for this stubborn discharge. This is not always easy to do, as some fuse boxes are located in hard to access places and often the alarm can be set off as you move around the car. This Audi was not too bad though and soon I am on to the culprit. As soon as fuse 15 is pulled, the drain could be seen to disappear and after several repeats of the same test I am happy that I am heading in the right direction.
My next step is to study some vehicle data and establish exactly what consumables are powered via fuse 15. I am now faced with just three possibilities, as fuse 15 supplies the instrument cluster, seat and mirror position memory module and the air-condition module. The instrument cluster is relatively easy to remove and disconnect and fortunately I strike lucky first time. Whilst watching the scope trace as I disconnect the instrument cluster I can see the current drop instantly. BINGO!
Keeping the customer “in the loop” is important for obvious reasons and as I had reached the limit of her agreed initial spend, I invite her to call in and see my findings. Even the untrained can gain an incite into the complexities and with some explanation, she was able to understand what had been found. I offered her the option of a replacement instrument cluster or the somewhat cheaper alternative, of a relay fitment, which would serve to kill the circuit at switch off. I explained that there maybe some minor implications, like the time and date would reset at start-up, but this was a small issue for her and she opted for the relay to be fitted.
Once I had fitted the relay, I needed to confirm the fix and after performing the same test as before, I was disappointed to see that a 360 mA current draw still remained. Back to square one! Well not exactly, after a few moments pulling fuses, I quickly established that the fuse that supplies the engine ECU was responsible for this new drain. Time for a cup of tea and some thought!
As often happens in our job, the cup of tea can work a kind of magic and as I return to the Audi I am pleased to see that the current trace has dropped to almost zero. I measure the time taken from doors locking, to full sleep and it is exactly fifteen minutes. A quick look at my amps clamp to make sure it still has a green light and my confidence starts to return once more. I still need to repeat the test and after seeing the same result several times, I can finally claim the fix.
The following image shows an uninterrupted 33 minute, 20 second capture of current flow. At half way, the point of complete sleep is clear to see.
