ABS diagnose/repair

[dave45056]

One day my ABS light came on. I checked it out and sure enough there was no abs... when I slammed on the brakes, everything locked up.
Everyone said it was the wheel speed sensor. When I asked how to check which one, the consensus was "have the codes read at Autozone".
First of all, the autozone does not read abs codes. Also, my car is OBD I, so the code reading is different. So I decided to dig into this a little more.
I took out the passenger side dash cover and glove box. The abs controller is on the right side. Then I disconnected the cable to the controller, and started probing. My connector was not 55 pin like other e36's but I had the Wiring Diagram. I tested for continuity at each wheel speed sensor. I got 1060 ohms at each one except the front right which was at 2 mega ohms. So My problem was indded a wheel speed sensor. I attached a copy of the wiring diagram I used.

I also thought that maybe the pump was bad. There was a lot of information about the ribbon wire in the pump needing to be replaced. I found these 2 links which may help anyone trying this repair:
http://www.staffordnet.net/repairs/b...ump_rewire.htm
http://www.thetremmels.com/bmwabs.htm

Lastly there is a way to force the pump to cycle. This can be used to check it and also bleed air out of the system.
Pull the grey ABS relay from the fuse panel under the hood. Jumper pin 30 to 87 and you should hear it pump away. Bleed the brakes as you normally would, cycle the ABS, then bleed again. Sounds like a lot of fluid, I know. You may need 3 quarts to do it right.
Hope this helps someone out there.

[iananderson02]

activating the ABS via jumping the relay really isn't necessary to properly bleed the system. The best way, BY FAR, is just to do it the old fashoned way:

Get a good old gatorade bottle and drill 2 holes in the cap. one hole will stay open and the other will be sized to accept the proper size clear plastic tubing. size of plastic tubing is determined by whatever size you can get to fit tightly over you bleeder screws.

put a small amount of clean brake fluid in the gatorade bottle and insert the tube far enough that the end of the tube is submerged in the fluid. the other end of the tube is put over te end of the bleeder screw. open the bleeder and have a helper pump the brake pedal up AND down slowly (yes i know this may seem wrong but it's not, trust me, i have 5+ years of BMW specific expierence gained at an large independent BMW shop and this is by far the easiest and best way). the tubing should be routed UPHILL from the bleeder so the bleeder is not the highest point between the calpier and the bottle. the fluid will be pushed out of the bleeder UPHILL through the tubing. because air is lighter than brake fluid the air will naturally rise and will not be sucked back into the system. only a small amount of fluid will be sucked back into the system, this will have no negative consequences.

the bleeding process is essentially complete when NO air bubbles are visible in the stream of fluid exiting the caliper. if you are obsessive like me you should close the bleeder when your assistant is on the downstroke. let the pedal come up after the bleeder is closed and repeat the process maybe 3 times: each time opening the bleeder valve, pumping down slowly, closing the valve before the pedal bottoms out and releasing the pedal (letting it return to the top).

move on to the next wheel and repeat the whole process. you will have great results for little to no cash spent on tools (except a refreshing bottle of gatorade and a good 6 point, 7mm box end wrench). i have used power bleeders made by snap on, blue point, and all the cheap pump till your arm falls off companies (bavarian autosport, bmp etc.) and they all suck compared to this method! Good luck, and really, dont worry about cycling the abs pump, read your bentley manual or bmw tis, its not necessary at all...

-ian

[dave45056]

Ian, Are you saying that you don't need to cycle the abs pump to bleed the system even after removing the abs pump and reconnecting it? At bimmerforums there was a lot of discussion about this. The theory is that if the pump is not actuated, no fluid gets cycled completely thru it. Makes sense to me.
By the way, I like the method you describe to bleed the brakes. Sounds like it will save a bunch of brake fluid. I'm just not sure that it will get it all the air out after doing a pump R&R. Are you sure?

[iananderson02]

While I can't guarantee that this method will work 100% of the time on 100% of all cars I have used this method countless times on e36 (and many other BMW's, and other makes too) cars that had essentially dry brake systems. When all the lines and calipers are removed it doesn't take long for the system to go dry (unless you cap the lines somehow). Dry may be a relative term though, the vast majority of the cars i have worked on did not have the ABS pump removed (several did though and the method above worked with no problems).

On a side note, i'd like to be the first to correct myself. The e36 bentley manual does have notes regarding special procedures for bleeding the brakes of cars with traction control. It says this procedure should be done by a bmw dealer. My experience tells me that this is not at all necessary. At the shop I worked for we never treated any car differently from any other, traction control, abs, whatever. For several years we struggled with a very expensive pressure bleeder only to go back to the old school method above. It always proved to get better results.

Also, the bmw tis states that a special procedure is to be done on e36 cars up to 09/1993 fitted with ASC+T (which includes NO 318ti's, all ti's were made later than this) where the ASC+T pressure accumulator should be bled (it's located under the left front wheel well plastic liner). In reality I don't think this is ever done and I have never seen any problem with not doing so. Also, the bmw tis reccommends this old style procedure I outlined above almost exactly for ALL cars with abs. For non ASC+T cars no mention of any activation of abs pumps exists. For ASC+T cars it is unclear exactly what role the computer plays in the bleeding procedure but it is clear that this standard old style method should be used throughout the procedure.

I would truthfully just try it out. I can almost promise you will see great results. Take a careful test drive after any brake work and carefull check all connections for leaks. I don't think this method is a bid fluid saver, you will still go through 1-2 liters of fluid but either way, be exhaustive, don't skimp on brakes. You can't do without them... Good luck...

-ian

[dave45056]

Thanks for the great information about bleeding the brakes. I had intended this to be a thread about the abs system on the ti, however. Do you have any similar tips about diagnosing/repairing the ABS system? This is where I was having trouble finding information and thought I would share with the group what I had found and done. I also have a Bentley Manual and the TIS, but they say "bring it to the dealer" when it comes to the ABS system.

[318iS]

Originally Posted by dave45056

I also have a Bentley Manual and the TIS, but they say "bring it to the dealer" when it comes to the ABS system.

hahaha thats ridiculous... why the hell would i buy a manual that tells me to take the car to a dealer... isnt the whole point of a bentley manual to avoid expensive dealer rates ? ? ?

[mohaughn]

I don't know what the TIS says, but if you have ABS I have always heard that you have to cycle the pump if the pump is completely dry.. And the right way to do that is with a BMW diagnostic computer. So if a repair manual says to take it to a BMW dealer that is because the right way to do it requires a special tool that the average home mechanic is not going to have... I've never read a haynes, chilton, or bentley manual that suggested using the jumper method instead of a diag. computer. They would get sued when people started frying their electronics from not doing it right.

My ABS has failed on my Ti. I don't remember the exact code but it basically points to the pump having failed. I've always assumed it was the ribbon cable issue but never looked into it any further.

If it was me and I totally removed the ABS pump or put a completely new pump in I would want to make sure the pump was cycled before taking it out on the road.. But I have seen plenty of DIY articles that say to bleed the system, take the car out, slam on the brake to activate the ABS, then take it back and bleed the system again.

[iananderson02]

I understand Bentley's recommendation to take the car to the dealer, no one wants to get sued, but truthfully, we, at the independent BMW specialist shop (who by the way are equipped with the MoDIC BMW factory diagnostic computer and are capable of doing the bleeding procedure the hard/"proper" way), have never ever jumpered or in any other way activated the ABS when bleeding brakes. Secondly, the BMW TIS (technical information system, basically a huge electronic manual for almost all bmw's that includes repair procedures, diagnosis instructions, specifications and the like) says nothing about using the diagnosis computer for any e36 built after September of 1993, which includes ALL 318ti's. The bentley manual notes to take the car to the dealer only reccomends to take the car to the dealer if it is fitted with "AST" (ACS+T). It also, incorrectly according to BMW, reccomends the use of a pressure bleeder for cars with ABS. Here is entire issue, summed up as I see it:

BMW TIS says:
-e36 built before September 1993, with ABS and ASC+T must be hooked up to the MoDIC or DIS or GT1 or similar diagnostic computer. The old style method is still used while bleeding but the pressure accumulator is also bled in addition to all 4 wheels. The computer is NOT used while bleeding the calipers, only the pressure accumulator.

-e36 built after September 1993, with ABS. NO computer needed or mentioned. No pressure bleeders should be used. Bleed as I have outlined in detail above.

-e36 without ABS or ASC+T (if this even exists, which to the best of my knowlege it does not). Pressure bleeders are acceptable to use but the old method will work also.

Bentley manual says:
-e36 with traction control: take it to the dealer, or in plain english: take it to the dealer because we don't want to get sued when you incorrectly jumper you ABS relay and fry you wiring harness, wreck your car and possibly more.

-e36 without traction control but with ABS: use a pressure bleeder when bleeding, obviously conflicts with BMW's info.


ME (not wanting to get sued also, but not afraid to give you the real scoop):
-all BMW's, regardless of fitted accessories, just bleed the damn thing as I outlined in my first post. The results are more than acceptable and no extra BS is required.

Hope this helps...

-ian

[iananderson02]

Originally Posted by dave45056

Do you have any similar tips about diagnosing/repairing the ABS system? This is where I was having trouble finding information and thought I would share with the group what I had found and done. I also have a Bentley Manual and the TIS, but they say "bring it to the dealer" when it comes to the ABS system.

This is where the Bentley manual is much more correct. Diagnosis of ABS system faults requires that the car be hooked up to a diagnostic computer of some sort. Peake research makes a very affordable plug and play diagnostic device for the engine but to the best of my knowledge no manufacturer makes anything that can read/reset ABS codes that is "affordable" for the home mechanic.

At the shop we use mostly the Baum CS2000, a very nice tool, but is several thousand dollars. There are several PDA based systems that are somewhat more affordable available as well as factory BMW stuff like the MoDIC that can cost $30,000 and more. To do the job right the first time and ensure the problem was fixed right and codes were cleared you really need one of these.

However for the really cheap/poor/frugal/motivated DIYers you can do alot without taking your car to the independent shop.

First: your resistance tests on the wheel speed sensors is a good start. I would take it a step further and swap the sensor with high resistance (front right i believe) with the one on the other side (in this case, front left) and recheck the resistances. This will rule out a bad connection in-between caused by corrosion or a bad wire of some sort. If the high resistance changes sides than you could probably assume that the sensor is bad. The parts are not all that expensive so just replace it after testing like that. If the resistance doesn't swap sides than it is mostly likely a bad connection somewhere. Start voltage drop/resistance tests to find the problem.

On a side note, I believe wheel speed sensors can be tested with an oscilloscope, but I have never done this nor do I have the knowledge on how to do this. Either way, I have the feeling this is out of the realm of most if not all DIYers.

Second: ABS relays are known weak points in e36 cars. I have heard a build date where the relay problem seems to stop but truthfully, i don't think that can be 100% reliable in all cases. If you ABS light is on intermittently replacing both relays: the red and grey (pn:61 36 1 393 404 and 61 36 1 393 403) is not a bad way to start, just for cheap insurance and elimination of one potential problem. However, I rarely recommend "throwing" parts at a car to try and fix problems, you won't usually get lucky. I like to diagnose things right the first time, and replace what is needed the first time.

Past that there are several online write-ups on other misc DIY ABS diagnosis techniques but it may just be more trouble than it's worth. Find an independent shop with a good group of technicians and a good diagnostic computer and let them diagnose and fix any ABS problem. THIS DOES NOT INCLUDE A SIMPLE BLEEDING PROCEDURE, YOU CAN DO THIS YOURSELF (if you have a few tools, a friend and a good flat place to work that is)!!!!

I would love it if anyone else has DIY ABS repair info. Even tech's with lots of fancy tools can still benefit from learning easier/better ways to diagnose/repair the car's we work on. This whole bleeding issue is just one example of this!

[bucksworld]

After working on the suspension, new struts and shocks with new springs belstein. My michanic did the job and now my ABS light is on. What did he do to give me this new mess. Does anyone know where to start? Brakes seem to work fine.

[bucksworld]

I took my TI to a friend and got three codes. First thing I noticed bad was the brake sensor wire was torn on left side. Could this be the entire problem or should I go for the bleed job too. There was no ABS light until they replaced my struts. Why three seperate codes now?

[bucksworld]

code 148 abs pump relay and code 177 valve load circuit fuse.....doed this mean replace the two relay fuses red and grey......

[mohaughn]

Do some searches on here or on bimmerforums.com. There are a lot of different things that can cause an ABS issue.

You can jump two pins on the abs relay, 87 and 30 I believe, and it will cause the ABS pump to cycle. I'm fairly certain if you do that an you hear the pump cycle it is probably a relay problem. If you perform that diagnostic and the pump will not cycle the circuit board on the ABS pump is probably broken. This is a somewhat common e36 problem.

A certified mechanic should be able to diagnose and determine exactly what the problem is without just throwing parts at it. You can try replacing the relays, but they may not be the problem. My car shows a relay problem, but it is really the circuit board on the ABS pump that is the problem.

[bucksworld]

Finally got my ABS light to clear and go off. I gravity bleed all brakes for 1 hour using the best brake fluid. I then replaces both relays at $70bucks. The light was still on at this point so my friend brought home the code reader which was real kool, i think it was a snapon brand reader. The thing brought up several codes for the abs system so we cleared all codes and started over. It still showed one code left--an 82code a right speed sensor. went to BMW and for $102bucks got a new one. That was it no more codes. And man do I have good brakes with ceramic pads. Also, painted my calipers black. No more stupid ABS light. That code reading computer was the trick but they may cost $3000.bucks or ask a mechanic friend to bring it home for the evening.

[applefan]

Raising this thread from dead!

my 96 318iC has ABS light on and I tested the following

1) 3 ABS fuses
2) shorted pin 30 and 87 of grey relay - pump is cycling
3) tested grey and red relay with a 9 v battery . relay latches just fine
4) tested 4 wheel sensors with an ohm meter. all look good. also tested it generates some voltage when the wheels were spun

What else should I be checking?
I was wondering where is the "slip Control module (ABS)" located from the picture Dave posted in the beginning of this thread?

Thanks for any help