964_944

Good morning all. I've had my 1991 964 C4 Cabrio for about two months now. Had some small bugs initially as the car and I got to know each other, but it's been running like a champ since resolving a vacuum leak that caused some stalling and hesitation.

Last Friday morning I had to do an emergency stop that engaged the ABS. Everything worked perfectly afterward, and the car was fine until today (Monday) when the "Brake" and "Differential" lights have come on and stay lit. The owner's manual says its a situation of low brake booster pressure and to wait for pressure to build up - but does not specify how long to wait.
Of course I read all of this AFTER I drove the car around for a 15 minutes and everything seems to be fine - no soft pedal or anything - but the lights never extinguished. I would think that would be adequate time for the pressure to build.

I don't see any evidence of leaks or anything in the front trunk area. Any ideas? Brake fluid is about 1/8th of an inch from the "Min" level - could it be something as simple as adding a bit of DOT4? Running the engine and pumping the brakes a few times?

Thanks!

911URGE

Yes, it could be that simple. Low fluid level will trigger an alert. No need to pump the pedal after adding fluid. The sensor is in the cap of the brake fluid resevoir. Although if the fluid did get to low you may need to flush the booster pump and accumulator.

Do you hear the booster pump running when you turn the key on?

Rocket Rob

Welcome to Rennlist. You want to keep the brake fluid level at the "max". I have found that if it is below that level, then you can get these warning lights.

964_944

Thanks! Hey Rocket Bob, Nashua, eh! I'm right up the road in Amherst, we should connect some time! I'm an NCR-PCA member, but don't make too many events as my schedule has not allowed it. I am working on a 944 to run DE and Auto-x - hopefully next season.

964_944

Well the problem seems to have fixed itself. Went out again and no more lights. I'm going to go ahead and add some brake fluid just in case, but so far so good.

Rocket Rob

Top up your reservoir. The lights will come on again if you don't.

964_944

Reservior topped up. Noticed that the lights do tend to stay on longer than the others. I wonder if it was a case of me driving off before they went out. If I wait an extra 5 seconds, they seem to go out and I'm good to go.

Rocket Rob

My ABS light takes a while to go out too. I have gotten used to it. Typically, the lights go out before I leave the parking space or garage. I have never timed it but I would say it takes 10-20 seconds.

BlueHeeler

I thought a light or two is supposed to stay on until you hit 3K revs.

Turbohead

sound like your pump is good I would flush and bleed the entire system. Start bleeding with the bomb first.by turning the key on and opening the bleeder valve.(only a couple of seconds)
I do have these parts if you need them but I don't think you will.
Elliot

Computamedic

Only if you have the common "clock" problem!! A bad solder joint in the clock will cause the alternator charge light to stay on until the engine hits the 3K revs but it's fixable with a soldering iron and about 10 minutes work.

If the hydraulic system is working as intended the booster pump should stop after something like 20 seconds after an overnight stop. If it takes longer it's a sure sign that the primary hydraulic circuit needs bleeding.

My car took almost a minute and a half for the pump to stop before the hydraulic bleed. Now it's 20 secxonds.

Regards

Dave