Brake pressure sensor
 

Anyone here replaced their brake pressure sensor--if so , was it as simple as removing the part and threading a new one in? Thinking I have a bit of trouble in that area

The pressure switch on the ABS module, right?
You'll need to get the ABS/Brakes bleed with the factory (or similar) computer that can open/close the solenoids in the ABS module.

I have no experience with the BPS, but there is this thread for TESTING it:
- How to test the brake pressure sensor (1)

http://www.bimmerfest.com/forums/att...1&d=1325966017

E39 have a brake pressure sensor? Is it tripped if there is a leak in the system?

I'm no expert, but, how the BPS is used by the system is explained in this PDF.
- BMW_30-PAGE_DSC_COMPONENTS.PDF (1.69 MB, 3562 views)

Let us know if that answers the question though ...
http://www.bimmerfest.com/forums/att...1&d=1363581439

You can read the output of that sensor in INPA. Should read ~150 bar when you stand on the brake pedal.

Thanks all--I gues I can't just unthread the part and put another in then--I was thinking about going to a pick and pull and getting one on the cheap and seeing if that cleared everything up--the Trifecta that is

Pull the codes and/or start testing the wheel speed sensors.

Thing is, when you pull out the pressure sensor, you don't want air to be sucked in. Then the fun begins...

While the BPS error 81 is often implicated in the trifecta, as mentioned in the referenced thread, I don't know of a single case reported here on Bimmerfest where that error code correctly pinpointed the problem.

In fact, I had the error code myself; and it turned out, like all the (known) others, to be a bogus reading, due to the fact that the diagnostic tools just can't tell a bad sensor from a bad computer indication of the sensor reading.

Luckily, you 'can' test the BPS without having to remove it, using just a DMM and a partner, as already explained in the BPS test thread.
http://www.bimmerfest.com/forums/att...1&d=1244440535

The cars brakes act funny from time to time--sometimes when I get on them with light pressure the pedal seems like it goes unexpectedly down about a 1/4 inch and the car brakes hard when this happens--but it's only happened a few times over the last 6 months since these lights have been on--that is the reason I'm thinking it's the pressure sensor

Quick question. My 97 540i has relatively new pads since I bought the car from the previous owner 65% good since I checked. My breaks seem to be really hard to press down. sometimes if I'm coming to a stop they engage and break but don't seem to stop the car when their supposed to. It takes forever to stop.

I don't know what would cause this, e.g., a leak of brake fluid would show up eventually, and you would think a loss of vacuum at the booster would too.

Testing the BPS seems simple enough with "flying leads" and a DMM; but, if it's intermittent, it might not show all the time.

I would hope cn90, JimLev, RDL, or any of the others more knowledgeable than I can provide guidance.

The pedal isn't hard to the feel--when I stated that the pedal fell 1/4 inch it fell and the cars brake came on to stop the car hard--as if I had layed down on them somewhat--

Poolman, how's the brake booster?
P.S.: Or maybe there's a seal going in the master cylinder?

Doru--hadn't thought about those 2 parts--this all started up back in September when I backed the touring int a tree--never had the lights come on at all and no braking problems--I have replaced tow of the wheel sensors and have tow that haven't been replaced--still have the ones that I remove, one from the front and one from the back. Thinking about using those on the other side and see if it changes anything. The lights will come on for a moment then go away and do that all day long. Sometimes when the weather is with high humidity the lights will stay on for an hour or so --don't know what to think--it's getting warmer here now--that will give me a chance to look more into the cause's.

Poolman-I would also inspect the suction jet pump. That is the Venturi device that's plugged into the intake tube at the F connector. The thin hose is a vent for the fuel pressure regulator. The thicker hose goes to the suction jet pump that increases vacuum (above manifold vacuum) to the brake booster. If any of the hoses are split, if the device is cracked or damaged or if the vac hose to the IM is not attached, etc., you would have these symptoms.

Of course, any of the above would not cause your trifecta but it caused my brake pedal to be low when my suction jet pump was not working right.

If it's the sjp, a quick /sjp F3 in the best links nets this:
- How does the BMW E39 suction jet pump (aka SJP, or sucking jet pump) work (1)
http://www.bimmerfest.com/forums/att...1&d=1320816243

New jet pump on the car about a year or so ago--it's fine--this has to do with the sudden stop that happened when I backed into the large Oak that without respect for my car damaged my tourings rear hatch--shame upon shame on that Oak--anyway the rant's now over and I thank one and all for their kind input

Hey, Poolman, I just thought maybe your piston ends of the brakes start to get pitted by rust - right at the edge of the rubber boot where they start to protrude. Why don't you check these out? This might be in line with what you experience?