DJF1

Ok... so under the drivers foot rest right? There are 2 screws on the side of it. I tried to yank it out and its not moving. Is there a technic here or I'm missing more?

Rob Edwards

Not under the driver's footrest. The ABS brain is above the footrest. Red arrow is pointing to the bail for the harness connector. Disconnect the battery before pulling teh connector or badness will ensue.

Should you ever need to remove the footrest, in the pic below, there's a machine screw under the black plastic cap obscured by the letter 'A' in the pic. Pop that off, remove the screw. Easy peasy.

TheoJ

hi, despite of what is said in the beginning of this thread: if your car has a RDK, find a diag tool and connect to the RDK (!) not to the ABS/PSD box. By turning the wheels you will see that the RDK shows ABS sensor impulses. And yes: a bad RDK box may cause ABS errors. There is one more possible issue: since the 928 has a digital dash, a frequency converter is used, FCU, relay XIX. This "relay" may cause errors if it pulls down the ABS signal.

Test with the RDK diag and diagnostic tool: drive the car slowly and watch the counters increment at a regular pace. If not, you can see which one is falling behind. Makes troubleshooting easy. In case of a sensor malfunction, the ABS/PSD unit (928.618.120.01) will show a fault in the ecu error-log. Be aware, the old style ABS (928.618.118.01) is a no-diag design.

Regards

hallowzeve

Howdy all,

Some more notes on this issue:

I swapped out the $peedo relay for a new one. no change.
I tested the resistance at all three plugs in the barrel for all four wheels, all good..
Visually inspected the front (In my case speedo drive ) drivers abs sensor and all related wiring- in extremely good condition.
Unplugged ABS computer by the dead pedal and fenderwall - all very clean.
I notice a couple things when I start it up.
Key ON:
Green light on psd lights up and goes out. No messages on dash

Engine started - immediate messages for a couple of seconds then Tire pressure system warning
Then PSD system off warning, then Airbag system off warning
all without moving the car.

Theo - Not having the diag tool is the problem I think we're all facing. I'm hoping someone is planning on bringing one to Thirdcoast here in TX in Nov. At the very least to delete the airbag code.

Isn't there a troubleshooting procedure somewhere on this. Does anyone have the pet they could share?
It's a pretty annoying issue and I feel like I'm shooting in the dark, any thoughts or suggestions welcomed.
Cheers,
Bil

hallowzeve

Oh and I don't have the oem tires and wheels on there. Do I need to bypass the rdk somehow?
Thanks
bil

Bertrand Daoust

I don't think there is any relation between the RDK and the PSD system.
Neiher between the PSD and Air bag system but...

Yes you can bypass the RDK and see then.
https://rennlist.com/forums/928-foru...or-to-rdk.html

What size of wheels and tires do you have?

Edit: Just notice that everything happen when the car is not moving so can't be anything related to wheels and tires size.

DJF1

ok.... so guess what it was.. the stupid fuse. Number 28. Now you will tell me, isn't that the first thing you checked? LOL... no! It was a great education though just to see where things are. I'm really happy that it was such an easy and cheap fix. Now everything work. Well not everything as I'm still working on some crazy gremlins, like the battery drainage. My multimeter registers only 0.14 and yet if I leave the battery on all night its going to be dead in the morning. I even did one by one the fuses, but could not find anything. Now ofcourse, my central locking is not working, mirrors and the sunroof has a ghost. All were working last time I checked! On quick question though. With the key off are the windows, sunroof etc supposed to be working or not?

TheoJ

yes, RDK and ABS/PSD are related, so is the FCU relay. Take the schematic, follow the little lines. The Airbag is not related. The RDK uses the speed pulses for each wheel to measure speed and log a pressure error at a certain speed. But if the RDK has a malfunction, the signal might become corrupt and the PSD will act on it by shutting down. Same for the FCU relay. Typically the FCU relay failure will make speed appear zero on the dash.

Fuse28? The ABS fuse ! Why not start there first .... LOL.
regards

hallowzeve

OK DJ, You're not alone.

I wish mine was as easy as a fuse, though it wasn't much better.
I was going back and re-reading the threads on this issue and realized I'd only looked at the abs sensors wiring, and/or a grounded condition. I went back in and pulled the abs sensor and it was completely caked with shavings. I cleaned it up oiled up the barrel and replaced it.
I also replaced the FCU, cleaned every ground point I found (inlcuding the one at the wheel)
Jumpered the RDK and replaced the abs sensor.

I now have the speedo back. I do still have a psd and airbag error.

I'd actually rather the airbag stay off. Now on the to PSD - since this car only has 56k on the clock, I'm sure it's been neglected.
Thanks for the help guys.
bil

TheoJ

Airbag may need a reset which will require a diagnostic tool. No other option.
PSD: check if the pump ruins and stops in a few seconds. That inducates it is pressurized. Often the pSD is ignored wehn doing maintenance and it needs fresh fluids every 2 years.

regards

Bertrand Daoust

Thank you Theo for the clarification on the RDK and ABS/PSD relation.

cold_beer839

Bumping this old thread since my problem was fixed.

Reference non-working speedo, odometer, cruise control, ABS non-working fault light, PSD non-working warning.

Ended up being a loose connection behind the ABS relay in the fuse panel. When driving the car an occasional bump would set off these warnings/faults and the next bump would turn them back off. Knew it was a connection issue, but it was hard to find. Had to finally tap out and have Brad at Digital Chassis in Durham NC fix it.

Chuck Z

Ditto.

My ABS/PSD issue turned out to be a faulty relay diagnosed and replaced by Jim Burton at Hendrick Porsche!

Rob Edwards

Chuck-

ABS Relay XV on the CE panel, or one of the relays on the ABS pump? Just curious.

Chuck Z

I don't know for sure. I pick the car up tomorrow. Will report back then.