The wiring appears to be the same for '89 and '90. But most important finding is that for both years, T23 pin 8 is connected to ground with a note on the diagram 'only if RDK is installed'.

The RDK controller communicates with the Digital Instrument Cluster through T23, pins 6 and 7. There is one RDK fault, code 9, that reports a bad warning bulb in the instrument cluster. For a car not equipped with the RDK factory option, the bulb would probably not be installed at the factory.

So, maybe the cluster is seeing ground at T23 pin 8 and assuming the RDK is installed, so it checks the bulb and reports the result to RDK, but since it gets no reply from the RDK controller, it assumes a 'system fault' which is reported to the driver by the digital display.

So, you might want to disconnect T23 pin 8 and see what happens with the RDK controller disconnected. Disconnecting pin 8 from T23 disables the cluster from seeing factory wired ground at Plug #3, pin 15 (Tire Pressure).

 

Really? I did pull pin 8 from T23 along with pin 14 and got that CONTROL OFF error message you displayed from the owners manual.

Pin 8 in the diagram is related to the RDK warning icon, is it not?

Nonetheless, I can pull that one pin and leave 14 connected and then as you said, pull out the RDK connector from the controller.

I was hoping to leave all connectors in place and pull just one or two pins and be done with it but I realize the system is far more complex then it being that simple.

Thanks for the new idea. I'll get to this when I get back to the car tomorrow and report.

 

I was just suggesting that if RDK was a factory option, there must be a way to configure the car that way.

It could also be, but less likely, that the Digital Cluster thinks there's a RDK 'Sytem Fault', when the RDK warning bulb is installed and no ground at T23 pin 8.

 

Borland:

Are you ready this report ... it worked!!!

I just pulled pin 8 from T23 and voila, no more RDK cluster display of any kind. And no warning icon either.

All the while I was able to leave connected the main RDK connector to the control unit.

This is way simpler than even having to make a bridge or disconnect anything else.

Hopefully now everyone will consider this alternative. It does not disable the system. It just stops displaying any RDK messages or icon which is the end result for all.

Good call.



PS: Now if only I could get that central locking issue resolved. Still working on it on another thread. Central locking button unlocks each time it is depressed but does not LOCK.

 

ROW '89 MY S4 had RDK as option M482 with flat disks. All or at least many ROW '89 GT had it as standard with CS wheels. They use same dash circuit board and most likely control unit but wiring harness is different. Pulling pin 8 seems like correct way to do RDK delete but will it work on all '90-95? They use several different harness part numbers.

 

Change of status....

I forgot that the "real" test of disabling the RDK would be when "underway." I started the vehicle and let it run thinking that because I had no display message, the system was disabled.

Not so. As soon as I shifted into gear and started to drive off, sure enough ,the same old irritating message appeared, Tire Pressure Loss.

So, apparently simply pulling Pin 8 from T23 is not the solution. How discouraging. Back to the bridge solution then unless someone knows which wire(s) actually do stop the RDK error messages from reaching the cluster display.

 

What happens if you disconnect the RDK controller with pin 8 also disconnected?

 

Just back from testing your suggestion...

Sure enough, with RDK main harness disconnected from the unit and pin 8 out at T23, no more messages.

So I take it the recommend bridge for this connector is unnecessary if it works this way?

To bad I have to pull the harness from the RDK controller. Where would you suggest stuffing it? And should the now open end be sealed somehow?

 

That's probably the better solution, as the current draw between the 2 and 13 jumper is several miliamps even with the ignition off.

Just wrap the RDK connector in a small plastic baggy and wrap tape around it to seal it off. Then use a nylon tie wrap (nylon cable tie) to hold it up under the dash.

Can you say how easy it was to access the T23 connector? It's located on the outboard side of the drive foot well. Does the connector half with the ground wire (pin 8) side, pull down after separating the connector, enough to facilitate removing the terminal?

 

Real quick.....To confirm Kevin's results, I removed the RDK disabling 2-13 jumper from my '90 S4, and also disabled RDK by removing the ground wire (BR) from T23, pin 8.

It would have been much easier to simply cut the brown ground wire at T23 where it exits the connector. So, you might want to go that route instead.

Here's how I did it.....

First, connector T23 is located under the dash on the outboard side of the driver's foot well. I found it much easier to work on connector T23 if I unbolted the mirror memory controller mounting plate.

The mounting plate is only held in place by one bolt one one end, and one nut/washer on the other end. These fasteners are easy to access with 10mm wrench. Just remove the nut and washer, then loosen the bolt. Letting it hang down allows the T23 connector to also drop down as shown.



To separate the T23 connector, there is a ribbed pull lock on the side. It pulls out in two stages. Here's the lock tab pulled out at first stage (about 1/2"). You can pull it out with your fingers. The next step actually forces the connector apart.



It's a tough pull, so I used an adjustable wrench...



The pull comes out this far to separate the two halfs..



Here's the female end apart with the pin 8 brown ground wire (BR) removed from the connector. The wire in the photo looks yellow due to the flash, but it is actually very brown.



But before I could pull the pin 8 terminal, I had to separate a plastic wire guide from the back of the female half (shown separated in above photo). The wire guide locks in place, so I used some cut off tips of nylon cable wraps as spacers to help pull the two apart.

I made a modified terminal extraction tool to extract the pin 8 terminal. It's basically a standard 0.093 extractor tool with a piece of aluminum wrapped around it. The 0.093 tool is the same outer diameter as the terminal, so it is too small to work. Wrapping the piece of aluminum around it makes it suitable. The aluminum piece is inserted in the connector and the tool allows the terminal to be pushed out. For the aluminum, I doubled up (folded on the insertion end) a piece of aluminum sheet from a Coke can.





Now with the Diagnostic Tester again. I get this result instead.. Notice the ABS is the same as with the 2-13 jumper.