m750rider

I have a 1991 S4 with a digital display that occasionally acts up.

On hot days, the digital display loses the ability to display the information correctly - it puts up too many pixels and obliterates the normal information - ODO or speed on the left, whatever is selected in the middle, and trip or timer on the right. Sometimes it will just display horizontal lines instead of too many pixels. A good rap to the top of the pod usually fixes it, at least for a while.

It is definitely temperature related as it never happens in winter driving, only hot summer. The AC system works fine and cools the car properly, but even after cooling down, it can happen. Apparently it is warmer inside the pod than in the driver's seat.

The digital information and calculations still work, it is not lost during the period of the crazy display, mileage still builds, fuel mileage, ave speed, all that stuff comes back just like nothing happened. Everything else on the dash works fine. Just the electronic display is bad.

I'm sure someone has had this happen to them - what causes it and what is the fix?

Thanks

Bilal928S4

I would say, check the four connectors in the back of the pod.

Tom in Austin

If it just takes cleaning up the connectors that's a good outcome b/c actual degredation of the LED display is a difficult thing to fix

Alan

Check your voltage @ hot idle at the jump post... I have seen this with low voltage conditions. Summer is much worse for this - especially when you live somewhere hot.

It could be this AND contact issues in the pod connectors - so I'd look at both

Alan

m750rider

After driving for over an hour in a warm summer afternoon I checked the voltage at the jump post yesterday and got 13.47 V at idle. My gauge was showing about 12.5 at that time but I knew it reads low. I assume this is OK and low voltage is not the cause.

I've looked on the wiring diagrams and haven't found where the digital display shows up. I did find the "info switch" but not sure if that is what I am should be looking for. Which connector on the instrument panel would be suspect?

Thanks

Leon Speed

Replace the battery strap, clean the battery connections and replace the fuse(s) for the digidash.

If you remove the pod you will find that the digidash has four large connectors on the back.

Ed Scherer

Converting Porsche 928 Interior Lighting to LEDs includes some photos of the instrument cluster and instructions for disconnection and disassembly that you might find useful.

The wiring diagrams for the instrument cluster (like the one for my '90) treat the cluster as a black box; you see the connections to it, but not the internal details.

The four connectors mentioned earlier are these:



and they attach to the edge of PC boards in the cluster:




If you dig into the instrument cluster deeply enough, you'll eventually get to this point:



The info display unit when removed looks like this:



and connects via this blue connector on the back:



Reseating all of the connectors mentioned above (and, ideally, applying some DeoxIT to all of the electrical contact points while you're at it) might fix the problem you're describing. Be especially careful when disconnecting the four connectors on the back of the cluster; the locking mechanism used isn't all that obvious and you can break stuff if you don't understand how it works; see the document I linked to above for instructions.

m750rider

Thanks. Your link reminded me that I had seen those pictures before and they are helpful.

Does the blue connector on the digital module plug into the PCB when closed up? Looking at your pictures that seems to be the case.

The module itself is still available from Porsche - there is one in the US and one in Germany. I am tempted to replace it, because I am not counting on the connectors being the problem, but I would like to know if the module is the display driver or if the PCB is the driver.

Also, if I replace the module, do I lose the odometer mileage and start at 0 or is the ODO function stored elsewhere?

m750rider

I fixed this problem last week by replacing the digital dash display module. Porsche had one in stock and I decided to get it before it become unavailable. On my 91 S4 anyway and the software version on it, I did not lose the mileage.