brake precharger

Trying to diagnose the front brakes locking up on their own, after a quarter mile drive. I searched with no luck. I suspect the precharger as it seems to be only the fronts. If I replace the precharger with used Ebay part will a dealer need to program it? Anyone had a similar problem? The car has 5.7, PSM.

You should be able to unplug the brake precharge pump to test out your theory. I believe it has a two-pin plug. Of course you will get PSM errors with it unplugged.

I have disconnected the precharger and the lights come on, and the brakes seem fine. I see an Ebay used part for $70. or so and will order it, but have seen somewhere that it may require a dealer to program the new part. Also, if I install a new part can I preload with fluid to help with bleeding, have seen that a special tool (durometric?) is needed to run ABS during the bleed process. Thanks for you response.

I have disconnected the precharger and the lights come on, and the brakes seem fine. I see an Ebay used part for $70. or so and will order it, but have seen somewhere that it may require a dealer to program the new part. Also, if I install a new part can I preload with fluid to help with bleeding, have seen that a special tool (durometric?) is needed to run ABS during the bleed process. Thanks for you response.

Disconnecting the plug disables the entire PSM system. Because the brake precharge is only a pump, it only runs when the PSM system wants it to. So I don't think the precharge pump is the issue you are having. If you disable PSM with the dash switch with the precharge pump plugged in, do you still get the brake lockup? Have you scanned the ABS/PSM for fault codes?

The switch on the dash doesn't have any effect.

My obd doesn't read the Porsche evidently. I'm working on that.

Quotes source post: 17189916

Ah, yes, that makes sense. Turning PSM off with the dash switch does not really turn it off, instead it puts it into a passive mode and PSM reactivates when you step on the brake. Unplugging the precharge pump disables it completely. I will suggest two things that probably won't make any difference. This process fixed random PSM errors for me: There is a pressure sensor on the ABS unit. Unplug it and replug it in case the contacts have some corrosion. There's a big multipin plug on the ABS unit. Unplug it and replug it in case the contacts have some corrosion. Pay attention to how the plugs work, the big one has a sliding lock that needs to be slid open. Prying it off will break it. IMO, the problem you are having is in the ABS unit not the precharge pump. They ABS units are pretty cheap on ebay, too. I would find a way to read the trouble codes first. And, if you remove the ABS unit or the precharge pump you will need to use Durametric or a similar tool to bleed the ABS system.

Will do. Thanks so much. I feel like I've been beating my head against the wall. The brake switch at the pedal was my next move, I hate throwing parts at a problem.

The PSM OFF switch does as the label says and switches PSM off well and proper. After switching PSM off it does not reactivate even when the car is no longer stable but it does not switch off the ABS...

codes: 4460 pressure sensor 4480 booster pump The replacement precharger arrived, and am told it won't require re programing the system. Not clear on where the pressure sensor is.

There are a lot of different variations of the ABS/PSM in these cars. The pressure sensor is screwed in to either the ABS unit or the precharge pump - depending on which variation you have.

5.7

What I meant is there are 17 different part numbers for the 5.7 ABS/PSM modulator and they are all a little different.

The ABS pump part # 996 355 755 54 I'm unable to find an exact replacement, see some that appear the same, usually as a boxter part.

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That part# cannot be correct. It probably should be 996-355-955-54. Did you read it off the label on your ABS unit?

Hmmm. I did. Stamped on top.

OP', your 996 has PSM which has different hardware from one with ABS. Differentiate between the two.

My 966 is an '02 year model c2, 6 spd. 3.6, with PSM, the edmunds identifies it as the "5.7" version ABS. The # stamped on the metal ABS block is "996 355 755 54". I have searched for hours and have not seen one w/ exact same #, plenty that look alike. I have driven the car 100+ miles trying to diagnose. It changes from applying front brakes to rears, sometimes no sign of anything wrong with PSM off, the next time I drive it the brakes start dragging inside of 3 miles. Same with PSM on (once they start to drag, it is a matter of yards before they are almost locked, cured by cracking the lines, the fronts brakes at the precharger, the rears at the ABS block) Sometimes it lites up the PMS ABS DRIVE TO WORKSHOP, most of the time no lights. Yesterday I drove it 8 miles to inspection station, had to stop twice to crack the lines, inspection no problem, no codes, drove the long way home (15 miles), no problem until I turned into the drive, 50 yards to the shop and it was locking up as I pulled into the shop. I have replaced the switch under the brake pedal, I ordered the precharger but by the time it got here the rears started. I have seen forum posts that show separating the ABS fluid side from the switching side. I'm leaning toward problems in the switch control side (no leaks), but it appears that is the side that requires ecu matching at the dealer. My preference is to know the parts are the correct ones and the old ones are the problem before I go to the dealer. Millersports read the codes for me, 4460 pressure sensor and 4480 booster pump. Am I right that the small connector on the abs is for the parking brake? Could it be the pressure sensor (4460)? Sorry for the rant, this thing is getting on my nerves. Thanks for any suggestions. Also, if anyone has seen or heard of this problem, I'd sure like hearing about it. It's burdensome feeling so special.

OK, the number stamped in the metal is the part# of the casting, not the part# of the actual complete ABS unit. It seems you don't have a Durametric cable? If you did you could read the actual ABS unit part#. Also, if you replace the ABS unit you or your mechanic will need a Durametric or PIWIS to bleed it. I do not think any of the other scanners will work. This is a picture of my ABS unit. It's not the same as yours because this is an '01 Turbo. See that round thing on the bottom right of the ABS unit, under the larger pipe, with the small bundle of wires? That's the pressure switch and it's not available separately. The actual ABS unit part# is also on a bar code label that's stuck on the bottom of the ABS unit. At least it is on mine. I do not believe that the ABS unit needs to be coded to the car, or that it even can be coded to the car. It must be the matching part number. There are only three things that typically cause brakes to apply when not desired. One, clogged brake flexible hoses. Two, master cylinder not returning all the way after using the brake. Three, problems with the ABS unit. Because you unplugged the precharge pump which disables the ABS and the problems went away, the most likely cause is the ABS unit. I'm not trying to give you a hard time about the part#'s . The Bosch 5.7 ABS is a family of systems used on every Euro car made from 1998-2010 and none of them are interchangeable. Porsche part#'s for the ABS units all start with 996-355-955 and the last 2 numbers are the variant: 02, 03, 04, 05, 06, 27, 28, 29, 31, 40, 41, 42, 46, 47, 51, 52, 53, 54, 55, 57, 58, 59, 61, 63, 93 are all valid part#'s and are all different. According to the parts catalog an '02 C2 with PSM should use a 996-355-955-54, but the only way to be sure is to either read the bar code label or interrogate it with Durametric. Why don't you call Parts Society or another Porsche specific dismantler and ask for an ABS unit for an 02 C2 with PSM and see what they have?

theprf- I hope you can see that the 955 is 755 on this block. I have seen others I believe, on Ebay, but no "54". I think 56 was as close as i got. Otherwise, my unit looks like yours, which means nothing I suppose. I agree with your supposition on brakes applying without input and agree that the abs (control or pump unit) must be the problem. Thanks for the info on part#'s. Right, I do not have a durametric (or a cable)(I only have a mac) not sure with my limited IT skills it would do me any good to have it. I'm sorry to say I'm pushing on this post. file:///Users/Administrator/Desktop/ABS%20Pump%20failure%20after%20Laguna%20Seca%20-%20has%20anyone%20experienced%20this%3F%20Possible%20solutions%3F%20-%206SpeedOnline%20-%20Porsche%20Forum%20and%20Luxury%20Car%20Resource.html This link raises a few more questions. If I get it right, he could replace the hydraulic (non-matching #) side of the abs keeping his switching side and not need to program the unit/ecu? Of course, he knew the hydraulic side was the problem (leak). I tend to think it more likely the switching side is my problem, but not sure how to confirm one or the other. Will call Parts Society as you suggest, have a couple of other calls out. It really puzzles me why I can't find anyone with any similar experience, even mechanics. Thanks for your input here. This is my first Porsche and love it, but if I can't keep it running I can't afford to drive it. Might have to go back to M-cars.

I think your ABS problem is mechanical in the valve block, probably because of corrosion or something like that making the valves stick. The black brake fluid in the reservoir suggests that it was not changed, perhaps ever. I can see the pressure sensor on your ABS unit. Did you try to unplug and replug it? Porsche Atlanta's web site says that the -52, -54 and -62 ABS units are all replaced with a new part number 996-355-955-BX which suggests that those three numbers -52, -54 and -62 are close enough that any might work in your application. I can't believe that there are no wrecked 2002 C2's with PSM around. Someone has to have your ABS unit.

I hope you are right, tho the fluid isn't old. Prev. O. was billed for fluid flush @39,678 miles (current 44,000 ), during 40,000 mi. service 4/6/18, fluid looks good. A close look shows the pressure sensor is unplugged. Have driven up to 15 mi with normal operation (dash lights on) with it disconnected. Later drove a few miles disconnected and they started binding. Just returned from 12 mile drive with it disconnected. At about 8 miles I stopped and reconnected p. sensor. Approx. 2 mi later the rears started binding. Popped the rear brake line and drove home, still disconnected. I have seen the "BX" number, will go back. "I can't believe that there are no wrecked 2002 C2's with PSM around. Someone has to have your ABS unit" Agree, their is one out there.