Voytek

After one day of checking it out, I have found the following interesting behavior of our (or maybe only my) electrical system:
1. With ammeter between Battery negative strap and car body, after turning ignition key ON and then turning it OFF and removing it, making and braking the ammeter probe connector can detect latched draw probably in most circuits, short of those which depend speed, acceleration /deceleration sensing, braking, etc.).
2. Even with interior lights OFF (these draw ~600mA each!!) and doors closed, door red lights draw jointly ~400 mA until the timer times out (about 10 sec).
3. Timer will not time out with hatchback door open - so close it and test current draw from inside, otherwise you will be reading extra 400 mA.
4. There is a relay (I do not know which one) that is armed as soon as ignition key is turned and then turned back and removed. This load draws about 80 mA, until door switch is cycled (door open and closed again). So, cycle the door or consider extra 80 mA in your reading.
5. I have some "latched" 80 mA load. With all steps outlined above, the drain current is around 100 -110 mA (still too HI) until ammeter probe connector is interrupted. Then drain is only 20 -30 mA with all other solid state devices connected:
-Radio,
-Alarm Unit,
-LE ECU,
-Cooling Fan & Flap Control Unit,
-Cooling Fan Amplifier, and
-Central Information Unit.
This problem goes away with electrical system connector Q disconnected (Cooling Fan & Flap Control Unit and Cooling Fan Amplifier are powered via this connector, however openign those unit connectors makes no difference).

Is 80mA latch draw an inherent problem with all 928 S4’s with flap control, or unique to my installation?

So, now the challenge is to go thought rest of connector pins and see which load latches. Problem is there are no more electronics powered directly from the battery bus via connector Q, and relays have different failure modes (once seal contact welds it usually cannot be broken by power cycling 100% times).
Any ideas?

SharkSkin

You can try disconnecting the pins on connector Q individually. There are at least two ways to do this; they both start with removing the ground strap:

1) Take digital pics of connector Q, enough so you have a record of where ALL the wires go. Disassemble the connector and connect the wires individually to the panel. Set up for your test as before when you narrowed it to connector Q. Pull the wires one at a time until the load disappears. Take notes. Connect it all back up and do it again, disconnecting wires in a different order. Repeat until you are satisfied that you know exactly which wire(s) are responsible.

2) Make a number of short (3"-4") jumper wires, each with a male spade connector at one end and a female spade connector at the other end. Use these to jumper connector Q to the panel and test as in (1) above... advantage being you don't have to disassemble the connector. I have a set of these that I use for troubleshooting relays, and they are great for providing a spot to connect test leads, manually making/breaking circuits, etc.

Voytek

Thanks Dave,
I will try it today. I have used male-female a single spade jumper on A connector but as Your say one should jumper them all before unplugging. I also misidentified Flap Control Unit by disconnecting Ignition Control Units - very smooth!!). So, it may be still Flap Control Unit (now I know it is on the passenger side, under the cover between seat and door). Maybe that is nature of this box to become latched with 80 mA draw when Bus X power is removed bur Bus 30 power is till ON?

T_MaX

FWIW, that control unit receives input signals from temp sensors, switches, flap motor, it helps control the rad fan(s) speeds (via the final stage), after run and controls the flap position.

Voytek

Thanks Curtis - yes there is quite a lot of inputs to it, including hood locked (or unlocked) input! It looks like I have found that mysterious 80 - 90 mA latch drain. It is that Cooling Air Flap Control Unit, specifically the second connector with:
- output signals going to cooling driver amplifier (2),
- Bus 30 input,
- Bus X input,
- Flap Motor control disk interface (4), and
- GND.

It appears that when X is OFF (ignition key out), Bus 30 still powers "latched" circuit, probably for that after shutdown fans "ghost" control. It never clears until Bus 30 is cycled. It appears to be normal operation since is draws ~ 80-90 mA (rather than few hundreds mA).

Maybe John Speake could fix that, could You John (other than pulling fuse out would be great)?

So, when you have early S4, and you do not watch how you test, you may end up with reading of 580 - 590 mA when system is as healthy as new:
1. Doors red lights - ~400 mA total (when testing with hatchback open and all interior lights turned off),
2. Relay (I am not sure which one), becomes armed when Bus X is turned ON, but only gets turned OFF when doors are open and then closed - ~ 80 mA (after lights timer elapses, otherwise normal draw + 400 +80 mA)
3. Flap Control Unit (if you have one) - ~80 mA till Bus 30 is cycled (after lights timer elapses), and combined with
4. Normal draw ~ 20 - 30 mA.

So it appears that ~100mA becomes normal draw in S4 with flaps control. This should prevent start, with almost any battery, by 4th weeks of not riding.

T_MaX

I forgot about the input from the hood switch :/ Good catch! When the hood is opened it shuts down the "after run" as a safety measure.

It appears that when X is OFF (ignition key out), Bus 30 still powers "latched" circuit, probably for that after shutdown fans "ghost" control. It never clears until Bus 30 is cycled.

Forgive me, it's been a while, what cycles Bus 30?

What about the alarm? Did you check to see what it draws when armed?


"output signals going to cooling driver amplifier"= Final Stage

Voytek

Hi Curtis,
Yes, alarm is not a problem. I have disconnected this load via electrical system connector - still 80 mA latch. The same way, I have tested all direct Bus 30 loada (via fuse or not), and I have identified that 80 mA latch goes away only when connector Q is disconnected, and specifically 2nd connector on the Flap Control unit. You are right, there is no ability to cycle Bus 30. I did it by playing with ammeter probes (in and out of ammeter) to clear the latch. So, it is solid state logic that is kept alive by Bus 30 once Bus X comes on. I guess there is not much we can do, but keep car running and deal with extra 80mA drain (or remove fuse with flaps open).

SharkSkin

BTW, bus 30 is direct to battery...

John Speake

Hi Voytek,
Have you determined that if the Fan ouitput stage box is disconnected, there is still the current drain ?

Voytek

HI John,

Yes, I have unplugged the Output Stage and drain was still there. It was when the second (upper) connector on the Control Unit is removed, there was no latch and drain drops to 20 -30 mA. Put the connector back it, turn the ignition key in and out and the drain is back at 100 - 110 mA. So, it is probably by design, Porsche thought 80mA is small price to pay to run those cooling fans of Bus 30 after key is out. To do that they must have required the box to have some part of the electronics active. There is nothing to shut it off unless there is some kind of timer, or maybe by simply replacing Bus 30 feed with Bus X feed?

John Speake

Hi Voytek,
There is a good write up of the flap/fan system in the MY87 Tech info. Section 9 page 8 states "Fans only run on within approx. 45 minutes after turning off the ignition"

So may be if you wait for that time, the draw current would then drop by the excess 80mA you have noted ?

Voytek

Thanks John,
I will try that. Which MY87 Tech Info You had in mind?

John Speake

Hi Voytek,
It's the "Technical Service Information 1987". They were issued every year to the OPCs ahead of the W/S manual updates. They have more info than eventually found its way into the WS manuals.

Jim Moorehouse sells these with lots of other tech bulletins on his 3 CD set.

Let us know how you get on with the 3/4 hour test !

SteveCo

Guys;
Not to in any way undermine the efforts to define or locate current leaks, I will point out that my local Audi dealer mentioned in passing that most cars on their lot run the battery down when left standing unused for 5-6 weeks. I assume this to be the result of normal current drains...coupled with under-charged batteries, to be sure.

I think it is advisable to consider installing and using a battery tender in any car that remains idle for any length of time. Obviously, finding and fixing current leaks remains a very good ans necessary practice, but it seems to me the 928 can have "normal" drains in excess of 500ma from time to time, leaving one with a dead battery.

While a battery tender is typically standard fare for stored vehicles, I find myself using mine during the "driving season" when the car is to be parked for even a few days. Food for thought.

Regards,
SteveCo in St. John's

John Struthers

Steve, all,
FWIW update on earlier reply.
I did look up the Battery check and care section in my 82'MY Owners Manual.
Page 74, last paragraph:
"A battery loses its charge when not being used, so if the vehicle is laid upfor any period,
the battery should be charged approx. every 6 weeks to keep it in good condition." blah, blah, blah.
On the other hand the old Ford F-150 can practically hibernate and after cycling the key -I pressure-up the fuel rails after a long Fort nap- she cranks immediately..
No mention of discharging battery's in the Ford Manual. Less stuff maybe ????