1990 928 S4
My Tire Pressure warning light was constantly coming on. I had to inflate the rear tires to over 44 lbs. to get the silly light to stay off. While doing my pre-race inspection, Marc Thomas commented that my rear tires were wearing too fast in the middle, a sign of over inflation. I told him about the Tire Pressure warning and he suggested I bypass the RDK computer. The RDK warning system was installed on the 928 from 1990 to 1993.
I had read that the RDK computer remembers it prior setting, so I inflated the tires to 44 lbs. and checked to make sure the Tire Pressure warning light was off. I then disconnected the battery.
The RDK computer is located on the driver's side, under the dash. Marc had made up a bypass wire for me (for sale at DEVEK for $15 including instructions). I would be easy enough to make, you just have to get the right male plug ends, but for $15 it wasn't worth a trip to Radio Shack and figuring out which plugs I needed.
I stuck my head under the dash and found the plug. I had to release the clip on the wire side and pivot the plug out. I then installed the bypass wire in plugs 2 and 13. I then taped up the exposed end, and used nylon ties to secure it in place.
I then reconnected the battery and checked the Tire Pressure warning light. I was still off. I then deflated the rear tires to 38 lbs. and rechecked the warning light. It was still off.
The whole process took about 15 minutes.
The RDK Bypass wire installed
Copyright 2000, George A Suennen