PDAS or ABS System Failure C4 1990
 

Hi Everybody,

it me again. I have another issue with my PDAS system. After excellent postings on my last thread I was able to track down an issue.

https://rennlist.com/forums/search.php?searchid=7679547

The new issue seems now a PDAS or ABS system Failure.( PDAS is the Transverse-Longitudinal Interlock warning light). Most recently I have intermittent an illumination of the PDAS, ABS and Central Warning Light combined with the horn. This combination of warnings are an indication of component failures either in the ABS system or PDAS system and with that both systems are disabled.

The strange thing is some times it does not show up at all, sometimes it shows up when I drive. Today for the first time it came up when I started the car. As soon I turn of the car and start again it is gone and most of the time it does not come up again.

I am not sure if I really have a component failure or just a lose connection or similar.

The electronic control does every time when you start the car a system check if all components in the system are working properly including the wheel speed sensor as soon you reach 7 km/h. Since I drive most of the time without issue its hard for me to track it further down.

Any ideas what it could be:

Electronic Control unit, wheel speed sensors, dual differential solenoid valve, slave cylinder, inter axle diff lock, transverse diff lock, transverse accelerometer or longitudinal accelerometer ?????????

I am thankful for any hint.

Thanks Orry

Last time i had the problem i replaced the ignition coils and the problem went away (after having replaced and cleaned many other components). And for a P-car part they're relatively inexpensive - usu around $50 or so.

Suggest you have the trouble codes scanned to confirm PDAS or ABS problems. It's very common for those lights and others to come on intermittently from leaks in the ignition system, typically coils or wires. Tons of posts here, usually referred to as "Christmas trees" where most/all warning lights come on.

Next, would consider inspecting long. and lat. sensors in the front end of the console. They tend to jam with metalic debris. Lots of posts here on that issue too.

I had a similar problem, it threw a code 34 that flagged the expensive 7 pin relay on the ABS pump. I got out cheap, Porsche wanted $175 for the relay, I found it for $65.

The important thing is to have the codes scanned, you can waste a lot of hours hypothetically guessing what it could be, I was thinking everything you are thinking now, and all of those components are mucho expensive if you buy them new.

I have a 1990 C4 that xmas tree lighted up when I first got it and it turned out to be the floormat pressing up against the brake pedal.

Make sure the floormat is secured away from the pedals! Cheapest and easiest troubleshooting tip yet!

Hi there, this may help - check the level of your brake fluid and make sure it's topped up to the limit. I had those same lights coming on after I had to replace the switch on the high pressure brake/clutch system. Another tip with the C4 - make sure your battery is in top condition. When my battery was below par, the central locking would suddenly unlock the car as a safety measure. Good luck anyway!!

Tried bleeding the brakes and PDAS system?

I had same problem a few weeks ago, turned out to be nothing more than a loose connection on the brake reservoir level float! It is amazing what little you need to set this thing off!!!

Hi guys,
My Porsche is a 964 C4 (1990). From time to time I had the PDAS and ABS warnings on together with the buzzer but it was not full time situation so I kind of ignored it. The past couple of weeks is nearly constant and I mean nearly cause it did happen 2-3 times to work normally. One more thing to add is that when all warnings lights are on ABS is NOT working and propably not the PDAS (traction control) as well.
So after reading around I bridged the 30 + 87 pins of Relay 34. NO warning lights and ABS is back on working.
My question..... does this mean that the R 34 is the problem and needs to be replaced. Will this fix the problem? If thats the case then I order it as soon as possible.

Thanks

Sounds like you found the problem!

Many thanks for your reply njansenv. Did you have the same problem? Have you tested it?
Unfortunately is not a cheap relay.......especially when it needs to be shipped to cyprus so need to double confirm it before buying one.
Anyone who actually tested the bridge of 30+87 pins? Does that prove that its the relay 34 faulty?

Glad I found this thread... maybe more answer will come up... I had all my lights light up twice already. Hope it's no biggie. ugh.

Bridging 30+87 will effectively do what the relay does. The relay 'receives' an input to connect those two pins. Joining them will permanently do what the relay is intended to - not a long term fix, but a good troubleshooting method.

I have a 1989 C4 with this problem. I have unplugged the relay 34 and when I lightly shake it, it sounds as if something is loose inside. Has anybody had this before? Would it mean that the relay 34 must be replaced as it would appear?