Podguy

Power from the battery runs to the top of the fuse panel. There are about five red power leads of different sizes. These can be disconnected. There is a possibility that current is leaking inside the fuse panel. After disconnecting those you should not see any current draw.

One strange thing I found on a BMW was a bad solenoid. On occasion the solenoid would get into a place where there was a connection between the battery and starter. I did not take the solenoid apart since the starter was an exchange, but I suspect there was a burn spot on the wafer inside that was making a connection. When the solenoid was in this position it would drain the battery in a half hour or less. Granted this is more then you are seeing but there could still be some minor drain. The main battery lead goes directly to the starter. Disconnecting there really isolates things.

Good luck - it does sound like you are on the right track.

Ed Scherer

I believe 35 mA is about right. I think 20 mA to 40 mA is normal; my '90 S4 is around 35 mA. Others report similar numbers.

Alan

Yes - anything around 30mA is OK. The best you can do is likely about 15-20mA on a perfect car - few are - usually due to aftermarket stuff (radio, amp, add ons, telephone, age induced leakage etc).

You have stock alarm, ECU memory and radio memory to deal with.

With a stock battery of about 70Ah - 50mA takes a long time to discharge even down to 75% capacity - (e.g. at least 2 weeks with plenty of power left for starting).

Even 75mA did not really explain a 2 day discharge unless your battery / alt had other issues.

Alan

Alan

BTW - pulling all the fuses doesn't eliminate all power draw - not even close.

There are plenty of circuits that are unfused and always powered.

Alan

Ducman82

working on an 88, i am finding the same thing. about a 71ma draw. traced it to the factory alarm connection at the CE "E " plug. disconnect that, bam, down to like 15ma. if that. can the stock alarm have a short that draws to much?

worf928

Alan

FredR

My recent earth leakage issue seemed to be resolved by disconnecting the device that signals whether the rear hatch is closed [or not]. Dave's post above might explain the logic if a false signal kept other circuits in the alarm system energised. The probable reason why this happened [I suspect] was because the latch insert had disintegrated [yet again] as I duly discovered!

GregBBRD

Current draw and dead batteries are completely dependent on battery condition when the car is parked.

70 milliamps will draw a 1/2 charged battery below cranking amps pretty quickly....certainly in a couple of days.

The target we shoot for is 32 milliamps on a stock vehicle.

worf928

I think I wasn't clear on the context here. I didn't imply that there were no more clues. There are always clues. But, once you are past the steps of pulling relays and fuses and move onto the CEL connectors and the direct to battery connections actually finding the circuit and diagnosing the likely cause of the draw can take several hours. Then actually getting to the source of the draw to repair can require hours of disassembly. Then there's the cost of parts. And re-assembly. Funny how most folks want you to put the 928 back together after you've fixed the problem.

I wrote ...

... which is in the context of people paying someone else for the labor and in the context of nearly 100% of the 928s on which I work. That latter context is: not driven daily.

The first X amps of draw down to the ~100 mA range can usually - in my experience - be diagnosed and repair estimated in an hour or two. After that it's very easy to sink several hundred dollars worth of time into diagnosing a specific part or localizing a problem circuit which will then cost high-3- or low-4-figure dollars to fix.

So, in all of my cases once the draw is ~100-150 mA the discussion is of the cost-benefit of correcting that last ~75-100 mA of draw. Since the vast majority of the 928s I see are driven at most once per week and most of those are already on battery tenders most of the time, most of my clients would rather be more diligent about using their tender than in spending labor and parts dollars on what is best described as gambling from an estimate standpoint.

If the context is driven daily, lots of start/stop relative to alternator-charge time then it is vitally important to get below 50 mA. And if you're not capable of doing the labor yourself then it will be expensive and more-so if you don't have access to labor that can really do this type of work.

On the flip side, even with 100-150 mA parasitic draw and a not-old battery you can, with no worries, take a weekend trip, attend SITM, go to the Sunday C&C, etc, if when you get back and then let the 928 sit for 4 weeks or 3 months you put it on the tender. These are the use cases I deal with.

Now, if you're at 250 mA or 832 mA (pick a number more than ~150-ish), you've got a problem that has to be fixed or you can't do the above without worries.

I *have* on several occasions hunted down and killed the parasitic draw to the 20-40 mA range. If memory serves all of those cases resulted in bills in the low thousand dollars ranges including parts and 'while you're in there items' and for those clients it was money they were willing to spend because of their use case.

Last, even with two-digit draw, your battery will last a lot longer if you keep it on a tender when you're going to let it sit for more than a week.

Of course. You have to have a mechanism and procedure for being able to run the car, operate all circuits, stop the car and get your ammeter into the circuit without breaking the connection (or you need an ammeter with a really, really big fuse.) And if you screw-up the last part you get to do it all over again. Of course, of you're looking at draws in the AMPS (plural) range then you can use one of the 'clamp' meters for the first iteration.

jpitman2

I like these ammeters where you have blade fuses - bit more difficult for us bullet fuse users.
https://www.jaycar.com.au/auto-current-tester/p/QP2251
Love the price reduction combined with 'Out of Stock' !
jp 83 Euro S AT 57k

Alan

Dave - yes understood - it can get prohibitive if you are paying someone else to do it, and most wrenches are not keen - because its also not very predictable work - easy to end up with a lot of effort and limited results. But I'm assuming most here will be planning to do it themselves...
With 'good enough' tools, a positive attitude, the discipline to be methodical, a reasonable debug & measurement methodology and sufficient understanding to know what to measure and what experiments to try - you can put a major dent in any excess current - but it will take time & some sleuthing.

Alan

gomez123

I had a draw turned out to be the electric antenna.

SwayBar

Alan, will you be finishing your 928 electrical systems book anytime soon?

And I would like to thank you for what you already have available, for free. It/you has taught me how to navigate and make sense of the wiring diagrams. With that said, I'd gladly pay you for it as it has literally saved me HOURS of frustration.

So yes, I agree that anyone with the motivation to learn, and a disciplined tenacity to solve a problem, can troubleshoot and fix a 928 electrical problem.