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Andyrt200

Brake warning lights on after fluid change

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I changed most of the brake pipes & rebuild the front callipers on the E39 recently so all the fluid was drained out very thoroughly. Unfortunately it was only when fitting the last front pipe to the distribution block / ABS unit that I noticed the extra pump for the traction control connected to the fluid reservoir & ABS unit. It occurred to me then I wasn’t going to be able to get the fluid flushed through that. But then I did some checking & found that wasn’t the only problem, it seems I should have kept the brake pedal pressed down a bit too.

 

So I did all I could do with out the proper kit to run the pump though the bleeding sequence & just blead the rest of it very thoroughly. 

 

It seemed fine, luckily we have a big smooth field / lawn so I was able to give the traction control & ABS a good testing, they worked fine, all seemed good. 

 

It was ok for about 200 miles till the ABS, traction control & the regular brake warning lights all came on together. 

 

There were a few fault codes but after clearing them “51 Pressure sensor, line” keeps coming back. 

 

I tried giving the traction control & ABS an even more thorough workout in the field to see if any bubbles that could be in there could get forced through. They did get a bit of a work out but the lights kept going off & coming on, entertaining when you are turning sharply with throttle wide open making the traction control work for a living, the light coming on clearly indicated the traction control was off! Nor did the ABS work with the lights on, they did both work fine when the lights went out. In the end I just turned the traction off & messed about doing donuts & drifting for quite a while, the new suspension really has made a big difference!

It was great fun but I do still need to fix it. 

 

I guess if there is a tiny bit of air trapped in the pump circuit it could be messing with the pressure sensor. The brakes are working far better than they ever have before with so much new stuff so I don’t think there is any air still in there. 

 

When I looked at the live data yesterday when it was still hot from messing about in the field it seemed to read sensible value, apart from occasionally going from 0 to -1 when the engine wasn’t running. The three warnings lights also randomly went on & off as its sat with the ignition on but the engine not running, but the pressure sensor reading  fluctuating from 0 to -1 wasn’t at the same time as the lights going on & off so I’m not sure if it’s connected or not. 

I had a look again this morning before driving it & oddly it was reading a minimum of about 8, but would still read ok when pressing the brake pedal.  We went out in it, the lights all went off & on randomly while driving but checking the pressure on our return it read a constant crazy high number over 100 (maybe 192 but I can’t remember off hand) constantly with no change when pressing the brake pedal. 

 

The one other thing I did while working on it was to disconnect the main big multi pin plug from the ABS unit as I had read in TIS you should do that before doing any welding on the car. 

 

I have rechecked that plug a few times but it made no difference to anything, including the current crazy high pressure reading. 

 

I guess maybe the best thing to do is to take it somewhere that they have the correct kit to plug in to blead the ABS unit properly? 

 

Or is there something else I can try before taking it to a garage, I really don’t like taking any of my cars to leave with anyone if I can possibly avoid it! 

 

I suppose it’s possible the pressure switch has gone funny, though it seems more likely it’s connected to the recent work.  

 

 

 

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So I’m even more confused after more some more checking. 

 

The three brake warning lights are now on most of the time. 

 

The error message keeps coming back as “51 Pressure sensor, line” but if I look at the live data it sometimes shows 0bar sometimes 291bar, however when it shows 0bar is never related to the lights being off, so it seems something else is going on. 

 

I think 291bar can indicator a faulty sensor. If I find a time it’s showing 0bar & unplug the pressure sensor the reading jumps to 291bar, then back to zero when plugged back in. Fiddling with the small plug & wiring for the pressure sensor has no effect on the reading. 

 

However if I push down on the big multi pin plug on the front of the ABS unit I can make the pressure sensor reading jump about to all the different odd readings I’ve been seeing. Which is strange as the pressure sensor is on the other side of the ABS unit & its wiring seems to be completely separate. But it’s clearly happening so something strange is going on. 

 

That big multi pin plug is the one I disconnected to do the welding, probably should have just left it alone! I have double checked the pins, they are nice & clean. It’s hard to see anything of the connections inside the plug but again they seem fine, its all very clean, I tried blowning them out with an air line but it’s still the same. 

 

It really seems like the connections inside the ABS unit to the plug have been damaged. If I hold the base (on the ABS unit) of the multi pin & press it down there is no effect on the reading. But if I just press down on the top of the plug that changes the readings. 

 

The ABS unit is very close to the exhaust manifold & the heat shield stops just below it for some reason. 

 

The troube is assuming it is the connections inside the ABS unit any second hand unit is likely to just the same having been through many extreme heat cycles. I guess a new unit is a very expensive thing to fit to find it wasn’t that at all! 

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2 hours ago, amazighman said:

You can get the ABS module refurbished for a quite reasonable sum

 

Ah right thanks, seems I have the common trifecta or 3 lights of doom from the ABS unit being too close to the exhaust manifold then...

 

Thanks for the tip, I see some people have opened theirs up, but I think I’ll probably go for the send it off option. 

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May not be relevant, but... my last car was a much-beloved E34 540 with ASC+T option - earlier incarnation of the traction control which was in 2nd gen in the e39.

 

So as it turned-out, I had my local BMW dealer do complete brake fluid changes ea.2yrs not just because I understood it required plugging-in to cycle the abs system valves in the right way but also because - since it was a standing BMW service recommendation and they do (should!/did!) discount older model service - local dealer (Wellsway, Bath - recently swallowed by Dick Lovett, sadly) would do the job for just c.£56+vat.

 

Yes, really -  only 3yrs ago when last used; I couldn't buy the fluid for that, let alone waste a Saturday morning jacking each corner in turn, wheel off, skin knuckles to crack bleeders/ supply beer to bored mate to actuate pedal.

 

Now - it well may be true that good diy info+practice works with the e39 abs:  I haven't read-up on that myself. But I'd suggest  if in doubt, call nearest dealer for brake fluid change/bleed quote - if you want it, it might be a pretty cheap check-out/reassurance before pitching-into full ABS repair

 

Good luck & please let us all know what you find.

Edited by Huff

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7 hours ago, Andyrt200 said:

 

Ah right thanks, seems I have the common trifecta or 3 lights of doom from the ABS unit being too close to the exhaust manifold then...

 

Thanks for the tip, I see some people have opened theirs up, but I think I’ll probably go for the send it off option. 

There is a guy on eBay providing repair service for 70 ish pounds , he used to work for BBA reman and he knows his stuff. Used him before and he is good tbh.

https://m.ebay.co.uk/itm/BOSCH-5-3-5-7-ABS-ECU-PUMP-CONTROLLER-MODULE-REPAIR-SERVICE-AUDI-BMW-Merc-ETC/292619021160?hash=item442173eb68%3Ag%3ALycAAOSwcaFZECgd&_nkw=bmw+e39+abs+module+repair&_from=R40&rt=nc

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6 hours ago, Huff said:

Good luck & please let us all know what you find.

 

I will report back. I may well get the fluid changed again by someone with the correct kit to pug in to cycle the pump, just for  peace of mind if nothing else. 

 

But for now I’m reasonably sure it is the wiring inside the ABS unit. I can shake the whole unit & it makes no difference to the pressure reading so I’m assuming it’s not bubbles. Just pressing down on the part that needs rebuilding makes the pressure sensor reading change. I have rebuilt things like that before & could picture what was happening inside. 

Then 

13 hours ago, amazighman said:

You can get the ABS module refurbished for a quite reasonable sum

 

That lead me to 

that confirmed exactly what I suspected about broken contacts/ wires inside. So hopefully it will fix it. 

Looking at other related threads it seems generally accepted getting the ABS unit rebuilt is no bad thing anyway as it going to fail sooner or later anyway! 

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