BradB

I have had my Brake Pressure light come on the last few days upon starting my '96 C4S. It will stay on about 30 seconds then go off.

All I know about it is what I read in the owners manual. It refers to a Brake Pressure Switch that might be bad if the light blinks. (it doesn't) That switch, btw, costs $200 at the dealer.

Anyone had this situation come up and subsequently rectified it? Not sure where to start and hate to have the dealer "hunt" around.

Note, the brake pads are fairly worn and due for replacement soon, though the sensors never wore through. Any connection with the pressure and the amount the pistons are now protruding due to thin pads?

I have another DE coming up in 60 days and I don't want this nagging light to become a real issue just before my event.

Phil

check your brake fluid level

STLPCA

Brad
Since you'll be chasing my tail, please replace your pads before Putnam.

Unless you burn into the sensors, they are reusable (if you want to & you're careful removing them).

No help on the light other than the obvious - check level & bleed/flush system.

Luis A.

Brad,

I recently researched the subject as I wanted to bleed as much brake fluid as I could out of the system in my C4S.

Your car has a pressure accumulator used to assist braking force just like a vacuum assist device would in a NA car. My understanding is that due to packaging constraints in the front end of the 4WD cars plus occasional positive manifold pressure in a turbocharged car, Porsche went the route of the brake pump/pressure accumulator approach on the Turbo/C4/C4S cars.

The pressure accumulator is located in the trunk on the passenger side and it's about the size of an orange. The pump which provides the pressure for this system is located in the nose of the car, in front of the battery and covered by a plastic piece.

This thread on the 964 board provides some useful info as well.

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=4;t=000864" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=4;t=000864</a>

Ray Calvo

From experience with a 1990 Audi Coupe Quattro that also had hydraulically assisted brakes, I would tend to agree with Luis. That car had similar warnings; took longer and longer times for the brake warning light to go out after a cold start. Cure was to replace the pressure accumulator.

As a check, just before a cold startup might pump the brake pedal a few times. I would bet that after 1-2 pumps (maybe immediately) the brakes will feel like they lost power assist. Might compare it to how many pumps it takes to lose power assist immdiately after shutting off the engine after a drive.

Get it fixed before going to a driver's ed. Last thing you want to do is lose power assist while braking at 140 MPH.

nels415

If I recall reading the manual, the brake pressure light appears on when the car is started until the pressure builds up. Then you can drive off. I've had my light appear on for over a year and just got back from a DE yesterday. My brakes seem fine.

-nelson

Autobahn

Brad,

as Nelson mentioned the pressure needs some time to build up. as long as the light goes off there is no problem with your brakes.
no need to worry.