|Vehicle details:||Audi A6|
|Author:||Dave Hill | www.londonroadgarage.com|
20 A / 60 A DC (low amps) current clamp
30 A (low amps) BNC current clamp
30 A (low Amps) large-jaw current clamp
*At Pico we are always looking to improve our products. The tools used in this case study may have been superseded and the products above are our latest versions used to diagnose the fault documented in this case study.
Recently I was faced with a customer who had completely given up on the idea of her car ever being fixed. The lady owner of a 2001 Audi A6 1.8 Turbo, explained to me how she has always had problems with the battery discharging. In all of the time she has owned the car, she has had to resort to jump starting it most mornings and has also been buying a new battery about twice yearly. She went on to say that an Audi dealer and a local auto electrician have looked into the problem, without success. In fact the dealer had told her that there wasn’t a problem at all, which is worrying. Anyway, this is the kind of challenge I like and I suggested to her that I ought to be able to fix it for her.
The car was presented to me, with a new “Silver Calcium” type battery sitting on the back seat, as the one fitted, although not very old, had already suffered from prolonged periods of total discharge. Using the low amps clamp that comes with the Pico Automotive Diagnostic Kit, I set about finding the cause.
Firstly I find it important to make sure that I am testing the vehicle in its natural state. By that I mean that it is of no use checking for an unwanted or “parasitic” drain, by simply disconnecting the battery terminal and connecting an ammeter. Electrical systems need to go through routines and sequences in order to shut down. Even after market alarms and locking systems will react to a momentary loss of supply that disconnecting the battery will cause. With this in mind, I carefully place a jumper cable between the negative battery post and the main terminal, taking care not to break the circuit and making sure that no small cables are left hanging. I need to use a jumper cable because the vehicles main cable is too thick to fit inside the jaws of the Pico low amps clamp. It is important that the jaws close fully to allow accurate current measurement. Now I am able to confidently see any current flowing from the battery.
My next step is to put the car through the normal routine that it would typically go through at the end of a journey. So I cycle the ignition on and then off, then open the driver’s door. Then, rather than closing the door, instead I manually flick the latch closed, which is enough to convince the vehicle systems that the door is shut (although this is not always the case). With the door now open I have easy access to the fuse box. Using the remote fob to lock and double lock the car I can step back to watch the scope trace.
As I study the waveform, initially I can see the current draw as the indictors flash twice, then I see a lot of disturbance caused by the interior lighting, as they do a “slow fade”. The detail that Picoscope captures, allows me to see the fact that the interior lights are controlled in a duty cycle manner and as the signal settles down we can see the steady current flow that the various control modules are consuming as they go through a routine prior to going to sleep.
In the animated image below we can see just how useful the oscilloscope is when dealing with modern vehicle electronics.
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.
So why was I seeing a different pattern to that which I had seen before, when the instrument cluster was still live? I had pulled the same engine ECU fuse in my earlier test and no drop in current flow was noted. I am not sure to be honest, but I wonder if maybe there is a dialogue between the engine ECU and the instrument cluster at switch off and now that the engine ECU isn’t having a successful handshake with the instrument cluster, it might be waiting a little longer to shut down. It might be the case that this vehicle normally takes fifteen minutes to go to sleep and that the cluster fault was disturbing the sequence. These are just my thoughts. but who really knows hey!
Once again Picoscope has helped me fix a fault that has eluded two other garages. Further proof (if more were needed) that the investment made in buying the scope and taking some training, has been a major step forward for our business.
Before I had the Pico, my preferred tool for this kind of test, was a good old fashioned Avo-meter. The analogue style meters display the current nicely. Looking back though, I think I would waste so much time on modern vehicles, as I can’t go and get on with something productive, like I can with the Pico. Being able set the scope running and leaving it for long periods whilst the Pico gathers data is a real bonus.
Do you still think that your hand held multi meter is up to the task?
May 13 2018
Thank you for your comments.
In many cases I would agree with you, but things are not always so black and white and I certainly don’t live in a utopian world where financial forces are just something that effects other people.
Had there been any safety related concerns surrounding this repair then yes 100% this “workaround” solution would not have been appropriate, but as there were no concerns of this nature and considering the value of the vehicle in discussion I feel that the option to proceed with a cost effective solution was acceptable in this example.
I am always happy to consider new thought processes though so perhaps you could elaborate on your reasoning some more?
May 05 2017
Well, I am not too excited about the fix. Good job for diagnostic, but the relay option should of not been offered. A replacement cluster would of been the only correct option.
September 24 2016
““The time base setting is for 50ms/div.. Why is the time scale displaying 3min20sec/div?”“
The collection time is set to 50 S/div. That is 50 seconds per division & not milliseconds, hence the total screen time of 33 minutes & 20 seconds.
Hope this helps
February 08 2016
The time base setting is for 50ms/div.. Why is the time scale displaying 3min20sec/div?
February 05 2016
Excellent case study I like to test for voltage drop across the fuses to show current flow save removing them and kick starting another module that then has to enter sleep mode
David barzelay- Israel
September 27 2015
It was fortunate diagnostic. That such a failure can Fooled
April 18 2015
brilliant! That fixed mine,it had the same problem thanks! But i got a FUSE light on my dash
October 17 2014
Awesome. never have I read something so detailed and to the point.
July 23 2013
We have a 2003 chevy trail blazer and have been currently experiencing the same problems…my husband said it was the cluster a well but it was to expensive of a fix for us at the moment…now that I am using it for just a few short trips a day I have to jump it everywhere..this was very helpful I will have my husband read an see if this is something he can do.
January 17 2013
I am working with Toyota (forklift brand) in Spain, here, we are facing many problems like this every day. Our procedure to find out the origin of the problem is: 1. Battery test (We test it with an Amperis Battery Discharger), 2. If the battery seems to be ok, we performance an insulation test on the main components (to put away humidity problems)and finally, if the problem was not eliminate, we go directly to the fuses method.
PS: Nice diagnostic Dave Hill. I think this instrument (Battery monitor) is quite interesting. Where i can get information about its applications in the forklift sector?
September 05 2011
Thank you for your information. Its very usefull for me.
I have hyundai trajet 2005 that have a battery problem. I noticed that every time I open the door, the dasboard blingking even I turn off the car. And stop blingking when I close the door. And a few minute before I lock my car using remote control, there are sound and blingking again. It stop while I lock my car with remote control but the led lamp in dashboard still blingking.
What do you thing? Are these the problem that cause the battery discharging?
Thank you for your answer.
March 24 2011
How do you set pico to record an uninterrupted signal of 33 minutes on one picture? Thank you for your answer?
January 12 2011
thanks for sharing this with us all and thanks to the other contributors too I have this fault on a DAF 45 so its given me new thoughts as to how to apply the pico to the job
December 13 2010
Simon, I made a piece of kit out of a battery isolator switch, (the type used by the ambulance service / AA van jump leads etc) using a battery neg cable with female battery terminal connected to one post of the isolator, the other post I attached a battery negative lead with a cut out in the eyelet to the vehicle battery terminal.
This enables me to connect the isolator between the vehicle battery & it’s battery lead. I can then turn the isolator to the on position, start the car, turn on/off as many components as I can find. Turn the engine off with the Pico low amps clamp connected & go & do something else productive while the car goes to sleep.
When I return, the car has run through it’s shut down cycle while the Pico recorded it.
It works well.
November 10 2010
Jon, can you explain your isolator switch again. Are you saying you have made a battery extension lead so you can get an amps clamp around the battery where the cables are tightly routed. Another tip is to knock the bonnet catch over so the vehicle thinks the bonnet is shut and lock the car; should shut down within 15mins on most if not all models
November 04 2010
A good article, we had the same fault on a Bora with the same level of current drain caused by the instruments feeding 12Volts into CAN Low.
We bought a Pico to get to the bottom of it - excellent piece of kit.
A battery isolator switch with a female post connector on allows you to disconnect the battery & run through start & shut down procedures as the car would normally encounter. Stops you letting the smoke out of your jumper wire!
July 27 2009
Another excellent article.
You might find the RS Components PR200 probe useful. (There may be a newer version now).
The jaws are big enough to take 50 mm2 cables, but it will measure down to less than 50 mA on the 20 A range.
Frequency response is from DC to 10 KHZ so it works well with a ‘scope.
Mark Pinfield, Mechanic, Ireland
April 20 2009
Good diagnosis. We have an intermittent battery draw from a 99 Corolla petrol and going to attempt to catch it with the scope
On another note in our garage, we had a 94 1.6 Carina E which failed the NCT(MOT) on high idle emissions. On 4 gas analyser, emissions were pretty random, 5 mins setting up scope and 1 min of taking traces and a tired lambda probe was at fault. The car had no codes as older Toyotas only show lambda fault codes for open heater element circuit. So the scope gave us a 100% confirmation that we were ordering the correct part.
Sheraaz Suliman -KC Auto, Cape Town, RSA
April 08 2009
Good story and thorough diagnosis - thanks for sharing.
GERRY WADE AUTO REPAIRS IRELAND
April 07 2009
Enjoyed your story, great diagnosis. I am considering parchasing a Pico scope and I am looking forward to attending a training course in Bristol in June.
April 04 2009
Great example, good read. I have heard about a BMW which had the same problem, it turned out that the owners neibours key fobs kept ‘waking’ up the vehicle when their cars were used. There is a mod for this on the BMW, however, this owner parked their car in a different place and the fault went away!
April 03 2009
What a brilliant way to put it I will remember that…good diagnosis well done and a good story too it…thanks.
April 02 2009
So 360 milliamp is enough to drain the battery overnight then? Never thought it would. Something new I learnt thanks.
April 02 2009
Hi Terry & everyone.
You raise a good point. The maths would suggest that a battery would not be discharged substantially in just one overnight period. But in the case of this Audi, the lady used the car several times a day but only for very short journeys (the school run type). A few days of this kind of use will see a battery become depleted & once it has done so, it is always going to struggle, unless a periodic fuller charge is applied.
We occasionally see cars that have a perfectly healthy charging system & no apparent drain, yet the battery state of charge is very low, due to insufficient charge cycles.
I explain to my customers that their battery is just like their bank account. You need to put more in than you take out, or you soon become overdrawn! It is an analogy that most people can relate too.
Thanks everyone for the positive feedback.
April 01 2009
Good job. I am still in aw how great the Pico scope is. I will have one soon.
April 01 2009
Well done story. Personable to the point and entertaining.
Modern Car Repair
April 01 2009
Don’t hesitate Chad, just buy it. I have several scopes, from $200 handhelds to a $5,000 Tektronix. The Pico gets used more than all the others combined. I’ve used it just like the author of this article several times. Amp clamps on a good scope are also great for fuel pumps, starters, alternators, pretty much anything that has current draw.
March 31 2009
Good diagnosis and brilliant information thanks.
March 30 2009
Excellent diagnosis and great insight into the fix. Good man!