GP White 928 S4

Just an update: Before I left town for a few days I removed the fan amp from the car for inspection. When I got back I reinstalled it as I intended to test the fan controller per the tips above. Ever since then I haven't had the issue, and I've driven the car since. So far the fans are behaving and functioning as designed. We'll see if this gremlin returns again I guess....

Mrmerlin

its a good idea to put deoxit 100 on the connectors of the plug this will enhace connectivity

Bales

Had a similar issue, drove me nuts for a couple of weeks, had to disconnect the battery whenever not using the car. Disconnected everything, cleaned contacts, and reconnected and eventually it ceased, am thinking it was a dirty connection somewhere. Wouldn’t discount it being a relay either as replaced some of those at the same time.

tlebovic

Thanks to this page I was able to diagnose that the Transmission temp sender is stuck closed - 0 ohms resistance at the 2 wires on the intake sensor.

Does anyone know of a way to bypass the Trans sender so that I can use the car until I can get it in to the mechanic after Labor Day?

Thanks
Tom
89 S4 175k miles now...

FredR

Tom,

To my way of thinking your post appears to be a bit difficult to comprehend. May I suggest you submit a bit more detail about what you actually measured and where you measured it. The gearbox temperature sensor gives a switched output that when at 110C the fans will run on at a speed equivalent to a direct voltage applied of 8V. When the temperature drops to 105C the sender should go to open circuit and that input will stop run on.

I assume your problem is that the switch is stuck in the run on position and thus will not stop the fans whn you switch off- correct?. This should be defeatable when you stop by disconnecting one of the pins from the sender circuit Whether it is a good idea to attempt such remains to be seen. Other inputs should keep the fans running and you hould be OK during normal running or so I would think. Run on is also infuenced by the AC pressure sender, the coolant sender and the switch on the inlet manifold sender.

tlebovic

Earlier in this thread Dr. Bob suggested that you can measure the resistance of the transmission sender at the wires going to the Intake manifold sensor since it's wired in parallel with the transmission sensor. Those 2 intake sensor wires , 1 green, 1 brown, is where I measured the resistance, showing near 0 ohms.

I was hoping that someone knew which wire in the spare tire area needs to be disconnected so that the trans sensor reads open and doesn't complete the circuit that switches the fan on.

Hope that clears things up a bit...

Thanks
Tom

FredR

Hi Tom,

Yes it is perfectly clear now- because the measured variable is a simple on/off function there is no logic decision to be made in the controller as I suspected there would be.

The logic simply decides if there is an open value [infinite resitance or a closed contact [no resistance]. The two wires come into contact at terminal three on the PLC box and that item is located in the cover by the side of the passenger seat or so I recall.

To solve your problem as you clearly understand one only needs to interdict the cable from the gearbox sensor and you can do this anywhere from the gearbox to the terminal on the PLC simply by snipping it and then splicing it when you have fixed the issue. As you also clearly understand the simple solution is to undo terminal 32- a 3 pin connector located under the spare wheel cover with 1 cable in the connector. With this intent I went looking for a 0.5mm2 brown cable with a green trace but after playing around for 10 minutes I had to give up as I was covered in sweat- it is very humid this evening!

If the above helps you great if not i will take another look tomorrow if some kind soul does not beat me to it as it is way past my bedtime here..

tlebovic

Thanks Fred. I will check tomorrow after work.

-Tom

Bales

Hoping this may help you: http://jenniskens.livedsl.nl/Technic...9/MyTip922.htm

The first diagram should give you some direction as to what is triggering what, and therefore to bypass what's possible.

tlebovic

So finding the wire was easy enough. It was in a connector shared with something else



I start to pull the connector apart and when my hand jerked back I jostled this connector and a wire broke off right at the edge of the pin



Of course moving it around to see how to open it to get the pins out breaks the other wire at the same point. I guess this is the good news since I could now take the thing to my bench and really look at it.
I figure out how to open it - 2 tabs to pry back on the side to get the top (other side) open and then you need to wedge open the tabs on the side shown to actually get the pins free. Still so far so good.

Of course my little 100 watt iron doesn't get hot enough to melt all the solder inside the pin so I have to break out my circa 1982 propane torch so I can pick out the solder and wire strands.
There was some white stuff at the end of the pin where the wire broke but none of the other wires seemed to be corroded in that way. You can see the ground wires in the top picture and they seem clean.
Back to the car. I prepare the ends, tin them, solder the pins on, insert them, snap the clip on and we're back in business.

Pull the connectors at the intake and don't have an 0 ohms anymore. Success!

20 minute job, including removing and replacing the spare tire in the well - another fun job since I can only get mine in one way - trying to find the right flat spot to put on the right side, ends up a 2+ hour adventure.

Both wires look to be red and green sort of faded to brown and the other plug is green and brown. Does anyone know if the polarity matters? Or what it's for?

Tom
89 S4

FredR

Tom,.

Cannot answer your question at the moment. Yesterday I took a look at the wiring on mine just in case you needed some follow up assistance, I tried to move things around a bit and the top barrell connector literally fell to pieces! Those are weather sealed connectors but why Porsche felt they needed such at that location is beyond me considering they have non weather proof connectors at the same location.

If nothing else I am pleased I discovered this and can rectify it easy enough- no hope for those connectors in the engine bay that carry signals for the ABS system?

tlebovic

Sorry for giving you extra work Fred.

Thanks for looking for me.

-Tom
89 S4

FredR

No problem whatsoever- pleased I found the problem- never seen anything plastic fall apart like that . The connector ferrules were fine so io just slipped some heat shrink sleeves over the ferrules and upon heating it releases some glue as well- purchased te things by mistake but finally they came in useful

As a heads up I found two cables that were brpwn on green- one of them in the barell connector. If your problrm is fixed all well and good you got the right one