Hi everyone. Summer in the UK has arrived at last!

I have read through the archives on this, but need help on diagnosis if anyone has a minute. Just spent £1500 on a service and ain't got much left this month....

Problem - Intermittent ABS/Diff/! warn with buzzer, now every trip, as soon as car gets up to speed -not necessarily on 1st brake application. Stays on after ! is cancelled, until engine off.
Brakes feel good under normal, heavy braking. Occasionally at slow speed stops, pedal feels temporarily wooden and ?pulses/judders under foot.

Following my own investigation: has had plenty of long enthusiastic drives (500 mile weekend), brake fluid steady at max, contacts on reservoir cleaned, were dry. 3 or 4 pumps on the pedal will bring on the lights as usual. Diff lock test works, (but won't switch on while warns are on.)

Just had 12k service at OPC - nothing on inspection/hammer apparently, apart from rear caliper slides lifting. Carried out rebuild rr calipers (inc drilling out/retapping seized bolts) and bleed system. Result - nada, except brakes now squeak! <img src="graemlins/crying.gif" border="0" alt="[crying]" /> Not the best 1.5k I ever spent, maybe...

For those of you still reading, my questions re next step (at an independent specialist):
1. NSR disc backshield is absent - would a cooked ABS sensor show on the hammer?
2. Any point in doing DME reset?
3. Could this be a sticking caliper slide on the front?

Any help much appreciated - those red lights are burning my eyes!!
BTW stock wheels and tire sizes, new Toyo Proxes allround.

 

Hi,
I'm suprised you're seeing warning lights with no faults logged - I thought the two were pretty much tied together.
I assume the pulsing / juddering you refer to at low speed is not simply the ABS?
Broken ABS sensors will cause the warning lights - but I believe will also show up on the hammer.

One thing I'm not sure I understood from your post - do you think the brakes are working normally (even though you get warning lights) or does it also feel like something is wrong?

Dave
90 C4

 

Dear Johnny,
How old is the brake fluid. You removed the caliper so did you have the complete system flushed and bled using the maint manual procedures and the bosch hammer.
The hammer will pick up a failed sensor. Please tell me they hooked up the hammer to PDAS/ABS control unit and not the diagnostic plug. You need a special adapter at the control unit to check this system up. Only DME, Airbag and HVAC are checked at the diagnostic plug.
DME reset is a waste of time.
Warn lights mean logged faults or an induced christmas tree effect caused by ignition shielding problems in the engine bay.
Why do I feel that your mechanic tried to read the PDAS/ABS system from the diagnostic plug?
Ciao,
Adrian
911C4

PS: Please explain what you mean by getting up to speed. What speed is this? Time delays like this tend to suggest wheel speed sensor, diff lock (however you have tested them) or the control unit itself. However need to know the exact sequence of warn lights first.

 

Er, £1500 for a service!!??
So, after the £400 + VAT service, what did you have done?
I take it they did loads of other bits as well.

I'd be interested to see what you get for £1500 at an OPC.

 

Hi,
I'm guessing 12K service at OPC starts higher than £400 + vat....

But - would also be interested in what you got for your money. Mine is at an independent now for it's 12K service, and I've given them a whole list of extra things I want done (new dist belt, new transmission oil, new door seal etc. etc...). I still don't expect mine to cost me more than £1K.

Dave
90 C4

 

Thanks everyone.
Adrian- preliminary phone call suggests that they DIDN'T use the ABS diagnostic connection - I'm not sure they even knew about it for the 964. They'll probably try and sell me coolant for it next..sigh....
Will let you know - the technician is to 'call me back'

John and Dave - am still at work, but will give you the breakdown (literally....)when/if I get home. I was expecting £800ish - I think I've got VAT on the VAT...

 

Johnny

Is there a 'specialist' near you? IMHO I really do believe that a good 'specialist' will do a better job, for less money, than an OPC.

BR
Piers

 

No word from Porsche dealer. Adrian, the light comes on at about 20+mph.

John/Dave
The service was rendered so expensive primarily by the brake work -£220 labour + £95 parts (s/plate kit, repair kit, damp plates x2) plus machine shop work (drilling out seized stud £45.

Next was 2 MOT fails : steering rack gator (£55 labour)and split front upper strut mounts both sides (labour £130 , parts £140 )
All inc vat btw.

So we're at £700 already, before they even changed the oil. Wey-hey.

The service itself :£365 labour, tappet tool £20(now we have to supply tools?, service kit £90,11 litres of mobil 1 single malt £90, plus a fiver in misc things. (like draining my (full) window wash reservoir of blue stuff and re-filling it with orange stuff with Porsche written on it.) Total for 12k service: £565 inc vat.

All so I can say FMDSH not FSH when I sell it. Are those two little letters worth it? Oh yes, and they did a half assed wash n' wipe too. Hmmm

Piers - I suspect you are right. If Brian Miller has a hammer, he's getting a call pretty soon.
I hope that I'm going to get some free work from the dealer, if indeed they did try and diagnose my ABS fault without plugging their ****ing computer into the right ****ing slot.

 

Johhny

welcome to the world of frustrating 964 ownership!! Its not the car thtas the problem - its some of the people working on them!!

My solution involves buying some tools and doing the 'basic' DIY stuff myself.

I'll let you know how I get on.

 

Dear Johnny,
I need to know exactly which lights come on. The sequence. At approx 20mph we are most likely looking at a speed sensor, diff lock or control unit. The fact that the ABS seems to work even with the lights on suggests a PDAS system component failure. This reduces us to diff locks, control unit or solenoid valve.
However to start with please give me the sequence of lights and all the lights that come on.
Ciao,
Adrian
911C4

PS: There is heaps of this in the archives. Also it is much easier for me if you do this via email and I keep the board updated. I cannot visit every day and this may cause you some frustration. The last person I helped it took a month or so to fix the problem. Cannot be done on this board. It is up to you.

PSS: What size tyres are you using. Please give full dimensions

 

Good to see you're on the hunt again Adrian! Sorry I can't help here Johnny but if anyone can it will be Adrian. He solved mine which revolved around my PDAS/ABS systems and they weren't just fault issues but deliberate skullduggery to fob my 964 onto me. Once Adrian had worked it out with me though, it's turned out to be the best dam%$d car I've ever had.

Kris
'89 C4

 

Have been reading your posts in the archives Kris. Hope my story doesnt turn out as nightmarish as yours sounded!

Like you did, I will correspond with Adrian via e-mail, and update the board accordingly.

As an update, the problem is more predictable now, allowing me to test it out today: odd things, feeling like ABS that's not very well, occur when the brakes are applied at speeds up to 22mph, after that the warn lights come on, and the brakes work normally but without ABS. Sounds like a complex fault where ever it is, but hopefully Adrian will help me get through it!

 

Good Luck!!!

CHeers,
Kris

'89 C4
'89 BMW 535I
'89 300ZX TT

It was a good year....

Flat 6, Inline 6, V6

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

There are a couple of things that can cause your problem.
First is that there is air in the brake booster and accumulator circuit. This system is rarely bled when the brake fluid is changed. The air causes pressure variations which may bring on the warning lights. You probably need to get your dealer to bleed this circuit as the pressure in this circuit is 180 bar.
You may also still have air in the brake circuit.

Second is a faulty pressure switch.
Both of these can be diagnosed by the dealer, it requires the pressure gauge to test.

The Bosch Hammer connects to the diagnostic plug to test the PDAS/ABS. The Bosch ABS tester connects directly to the ABS computer using a break-out box. This tester is rarely used.

 

Thanks GMS.
However your advice appears to go against Adrian's impression of how ABS faults are diagnosed on a C4:

[quote] Only DME, Airbag and HVAC are checked at the diagnostic plug. <hr></blockquote>

I appreciate all of this help. But I need to know exactly what the procedure should be here - if Porsche should have used the ABS/PDAS plug and didnt, then they may have advised me to have £400 worth of brake work that probably I didn't need.
I'm (still) waiting for their technician to speak to me - I also don't think they flushed/replaced the brake fluid.