struan

Hi folks, I have just acquired a 91 s4. It is really nice, just one small problem.
The tyre pressure warning keeps coming on showing all 4 tyres not at correct pressure.
I have checked pressures with 3 different devices but can not sort this out.
Does any one know how I can rest the system. Thanks.

FredR

No idea what happens in your part of the world but on my late 90 S4 to get the alarm signal to cancel needed silly high tyre pressures [about 45 psig I seem to remember] - this was more a problem during our hot season.

I "solved" the problem by jumping the RDK contacts effectively eliminating the system. Maybe you have a logic problem on your system causing the alarm to illuminate?

I think the general consensus on the RDK system is that it is more trouble than it is worth but ...?

Rgds

Fred

RKD in OKC

Do you have the Owner's Manual?

It tells you how to set the RDK. It involves setting the tires at a specific low pressure, driving a block or two. Setting them at a specific high pressure, driving a block or two, then setting them at the correct pressures. After doing this my RDK worked great on my 90 GT. Warning me twice of low tire pressure due to a nail and never falsing. Got tire fixed reset, then good.

A couple of times my mechanic set the RDK using the hammer. They always went off falsely within a couple of weeks. Had to go thru the reset according the the Owner's Manual to make them work properly.

I bugs me when I hear about people not liking the RDK because it doesn't work right. I never had any problems and it worked great when I set it according to the manual.

jcorenman

The RDK works fine, the most common problem is that folks swap wheels and wonder why it stops working.

The RDK sensors are mounted in the wheels (two sensors per wheel), not on the tire valve, so the first question is whether the wheels are original and the sensors are present. Without sensors, the tire-pressure warning always comes on. It can be jumpered, as noted.

The S4 came with 16" wheels, and the RDK sensors were positioned accordingly. Fitting 17" wheels with RDK sensors (from a GTS for example) requires a different mounting bracket to move the sensors out 1/2".

The sensors used in 90-91 were 2.5 bar and 3.0 bar in the rear- following the factory's pressure specification (which many of us believe is misguided). For the GTS this was changed to 2.5-bar sensors all around. So try 38psi all around and see what gets displayed. The sensors are pressure-switches, not analog transducers. They are either "on" or "off".

So the next thing to check is the sensors: Pull the wheels, clean up the inside of the rim and check the sensors, they will be stamped with a part# and/or pressure.

FredR

The main dealers could not solve the problem on my S4 even though they used the procedure in the manual and the hammer. The problem seemed to manifest itself more during out hot summers- why I have no idea to this day given it is supposed to trigger on "low" pressure. To keep the alarm off needed pressures that were "bone jarring"- and that was just not acceptable for me given they seemed to work much better when the pressure was around 38 psig- probably what Jim is alluding to.

When I purchased my current GTS the system was already defeated for whatever reason so never got to test it with the GTS wheels fitted [that generally I do not use but still have]. That they lowered the set pressure of the sensor for the GTS is interesting but it did come with a bit wider [255] rubber.

Rgds

Fred

struan

Hi again, thanks for the suggestions. I am away from home for a couple of days, so won't get to play with my pride and joy until the weekend.
It does have the original wheels, and I'm sure I noticed the owners manual in the glovebox.
My first 928 was an 80 manual and was void of all the electronic wizardry that this new acquisition has.
So please excuse what may be a dumb question. What is RDK, and where will I find the contacts to jump, if I get desperate and go down that path.
Thanks again.
I will report back with success or otherwise in due corse.

RKD in OKC

RDK is Porsche Acronym for Tire Pressure Monitor.

928cs

RDK: ReifenDruckKontrolle

jcorenman

Jumpering the RDK is more likely than not, but is easily reversible. Picture is here, post #2 (along with some additional discussion):
https://rennlist.com/forums/928-foru...to-repair.html

struan

Well here I am, early Saturday morn in my part of the world.
Happy to report I found the book of words (owners manual) and following the procedure therein I have reset the system and all is working as it should.
Thank you all for your help, much appreciated.
Such a beautiful day, I may just open the sun roof and go for a wee test drive. Fun, fun ,fun.

Dictys

Does anyone have a picture how the RDK unit is fixed between the mirror control and ABS Unit?

I wish to refit my RDK unit, but can't see how the unit fits in, i.e the on bolts the bracket around the ABS seem to short to fit both the RDK unit and the mirror control.