PDAS/ABS warning - a solution

Dave Wilkinson · Nov 11, 2004

Many of you will probably remember the continuing problems I have had with my C4 and the annoyingly consistent occurrence of the PDAS/ABS alarm when driven any distance. Over the summer the problem seemed to get worse (i.e. you could driver shorter and shorter distances before the dreaded alarm struck. I discovered that the problem was definitely temperature-related but that didn't help diagnose it.

In desperation I recently booked the car in to JZ Machtech to let Steve have a go at it. Interestingly, Steve insisted on looking at the ignition system before attempting to look for more complicated issues "" he said that many cars had displayed similar problems that were caused through HT tracking. Low and behold, he discovered that both the coils were showing very bad tracking damage, as were both the distributor caps and rotors. I'll post some pictures of the old parts on my web site later in the week if anyone is interested.

Having replaced both coils, distributor caps and rotors as well as a couple of "less than perfect" cable ends (sum total almost £400) is seems like the car is behaving at long last. I managed the drive home from JZM without once seeing the age old problem!!! I'd still like to get a few more trips under the belt before getting too enthusiastic "" but it's looking good.

Regards

Dave

Dave Wilkinson · Nov 11, 2004

If anyone is interested I have put some pictures on my web site of the offending articles causing my PDAS/ABS problems. You can follow the link to http://www.computamedic.co.uk/Porsche/PDASABS.htm. If you click on the lower image it will give you a higher resolution picture and you can clearly see the tracking on the distributor cap and rotor. The inside of the cable plug looks like a piece of 3 month old cheese!!!

Regards

Dave

Dave Wilkinson · Nov 11, 2004

Maurice,

I've no idea on the mileage. I have no evidence to suggest they have EVER been changed (the service history is patchy at best and non-existant for several years) so it doesn't surprise me that they were in the state they were.

I've been through more loops than you can imagine with subjects like wheel diameters, speed sensors, etc. etc. but all the symptoms I had could not be dynamic since I often got the PDAS/ABS alarm when the car was standing still!!! The car has got 18" wheels so if there were going to be a problem it would be a permanent problem.

Regards

Dave

Jamie Summers · Nov 11, 2004

I think this is more common than you might think. My (just purchased) 964 had a very similar problem with tracking and arcing - again diagnosed and sorted by JZM - hmmmmm, suspicious ...............

Jamie

Dave Wilkinson · Nov 12, 2004

Jamie,

Maybe that's why Steve is getting so good at spotting the symptoms!! He told me that he'd seen several cars with similar problems and that's why he homed in on the coils and distributors before looking for anything else. Prior to the JZM visit I'd had the car in with another (unnamed) independent who had spend two full days checking out wiring, connectors, relays, wheel sensors, hammer diagnostics, ABS diagnostics etc. etc. but obviously never thought to look at the coils and distributors. At the end of the day there is no substitute for good old experience.

I guess the good part is that I now know that much of the rest of the electronics are in good shape too.

Regards

Dave

plhorner · Nov 12, 2004

Please excuse my ignorance, being a lowly 3.2 owner I don't have to worry about diagnostics and ABS on my car. However, my brother in law has a 964 C2 Targa which is suffering from similar symptoms that you describe. Ironically its just had new dizzy caps and rotor arms but I'm not sure wether the coils were changed- problem still occurs. Anyway I digress, what is PDAS?

Guest · Nov 12, 2004

I think its the Alarm Phil.

Dave Wilkinson · Nov 12, 2004

Phil,

PDAS is Porsche's acronym for Porsche Dynamische Allrad Steuerung - which is the German description for the traction control system fitted to the C4 as standard.

Given my experience I guess it would be a good idea to have a look at the tops of the coils and see if there is any tracking evidence. It looks like my coils were tracking to the LT supply (rather than earth) and I suspect THAT is the main reason why it was causing a problem with the ABS/PDAS system. The ABS and PDAS systems are linked and controlled via a dedicated computer - and it's this computer that causes the alarm when it senses anything amiss (or THINKS there is something amiss) and getting 15,000 volts shoved up it's backside would make anything think there was something amiss!!!

Best regards

Dave