968norway

Hi, at start up, the pump starts but I get a warning light for the brake system if the car has sat for a day. Doesn't seem to happen after 1/2 a day. I understand that the system could gradually lose pressure when standing for a while. Is this normal?
Thanks

tdiquattro

Perfectly normal, but can be improved by bleeding the 4wd system and curing any slow leakes. Sometimes the actuators on the diff's can have leaky seals/connections.

There was a note about a failed accumulator causing the pressure to not hold up correctly. But I don't see that in a sealed system?

968norway

Ok, thanks, I am still familiarizing myself with the car. It is always nice to know what 'normal' is. It's going in for some brake work on monday, so there will be an opportunity to check things then.

tbennett017

Get a copy of Adrian Streather's book on the 964.It will help you a lot.

FeralComprehension

+1 Tom Bennett.

Behr 964

I get this same thing on my C4. Light comes on if left for more than a day or so. The longer it's left the longer it takes to go out. Just living with it.

968norway

I have Streather's book, very informative. I guess I haven't gotten to the part where it tells you things like this.

FeralComprehension

Send me a PM with your email and I'll send you Streather's PDAS article. Very informative.

(Offer open to all; I didn't write it...)

GilesHanna

Hi Guys.
Just looking to add to this.
Can has been driving beautifully.
Now warning lights are coming on and often staying on.
Brake pedal will go hard.....not good!
Often hard from cold and takes a little while to soften....30 seconds.
Booked into my tech next week to be looked at.
My question is. He is suggesting an accumulator, but I've suggested he does a proper brake fluid change and bleed.....after electrical diagnosis.
B. Fluid has not been done for about 2 1/2 years as I was advised it had been done prior to my ownership.
My concern is in replacing the accumulator, he'll do a decent bleed which means I could be spending £1000 for a part I may not essentially need....
Is appreciate some info.
NB I'm not trying to self diagnose, however 15 years in the car service industry. I tread carefully with diagnosis.

Harry Apps

Ignoring Clutch and Diff locks bleeding; full flush and bleed required at 10 bleed points for brakes - 8 (Calipers), 1 Accumulator and 1 Dual Solenoid Valve Block (these 2 in trunk).

GilesHanna

Thanks for the reply.
Anymore information appreciated.
Do the accumulators fail often? Not that I can see?
Reading your info I think this is my best first option.....and damn cheaper!
Is this a set procedure ? Common fault/cure . Thanks all.

fasterlaster

If the warning lights that are coming on are only the diff/brake then I would highly recommend doing a full brake bleed first. Components do fail, but this system is known to have that behavior of alarms if things are amiss in the fluid area. If that does not fix it then start to address it systematically with one o f the trouble shooting flows. Brakes are important, don't ignore the warning signs

Goughary

My accumulator failed. I had similar issues that you posted. Here's my advice...

First, most shops, including Porsche shops, have no clue how to bleed these cars, so hand it to your guy if you like, but if I were you, somehow without pissing him off, familiarize yourself with the DIY procedure in the DIY section on rennlist (I think it's Ricardo's, at least that's the one I use) and go talk to the guy about his procedure and make sure he knows the entire process. I think the latest dura metric that most shops use will activate the diff locks, but that's recent, and until very recently, if they didn't have a Bosch hammer, which many don't, they would leave the diff locks out of the procedure and you wouldn't be the wiser...so be sure they can do the whole job and that they know how, or do a full bleed yourself.
Once you have gone through a full bleed , let the car sit overnight, and in the morning put the key in and turn it to on without starting the car, listen to the accumulator pressurizing. Time it. It should take 45-60 seconds. If it takes a lot longer, you likely need to replace it. If it pressurized in the right amount of time, drive it for a week or so, and keep checking every so often. Of that time increases again to 1.5-2 mins like mine did, then you likely need to replace it....

Like others have said, diff lock seals can go bad and there are other places that may need attention, but the accumulator is you most likely culprit. But if it pressurizes within a minute, there shouldn't be any issue and move on to the next likely culprit.

Good luck with the search for the solution. Many of us w C4's have been there. Don't replace stuff *****-nilly, cuz that gets way too expensive fast. And very frustrating when it doesn't solve the problem. Just keep searching and asking questions and the answers will come. These cars seem complicated but 9 times out of 10 there is an easy solution...

LM964

Try this (something I will get round to at some point).

https://rennlist.com/forums/964-foru...procedure.html

GilesHanna

Thank you, Thank you guys!