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I'd forego the diode function and just obtain a resistance indication. I assume you have a digital multimeter probably with 1, 100 and 1000 ohm ranges perhaps? Or maybe an auto-range? Someone else can recommend the range but if something told you to use the diode test function then use the lowest range.

When taking resistancee measurements, besides a general inspection of the meter and leads that you should always perform prior to any use, short the leads together first to ensure they have continuity. If measuring voltage, always check voltage on a known live source in the range you are using on the meter before and after the check.
 

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Discussion Starter #42
salor24, josiahg52,



My multi-meter was set to the diode icon, there is no range setting, just min/max. If I touch the probes together, I get a very brief numbers flash before it goes to 0 or maybe 0L. I can try taking Ohm readings, what might they be? I have a suspicion that maybe the wheel speed sensor(s) because the ABS does not feel like it is working. Under very hard braking I can lock up the wheels and not feel the ABS pulses.


I wish there is a detailed (how to perform) step by step flow chart to fully test every thing to debug this out. I have found many 'how to' do not detail every tiny step that could make a difference. Don't assume anything by the person doing the tests.


Thanks again...
 

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What meter do you have exactly?

There is a difference between 0 and OL. 0 or zero would indicate a shorted diode. OL is overload and means you are reverse biasing the diode or it is open. Assuming how your meter operates, I'd expect an indication less than one volt and maybe an audible indication. That's even if this is the proper measurement to be obtaining for these sensors. I thought you measured voltage while spinning the wheel or somehow a magnet was involved. Fortunately, I've never had to do these tests.

Are you sure you are in the right mode? None of my meters have a direct diode check function. Buttons have to pressed after moving the selector switch. Personally, I never use the diode check function.

What is true is if while in the resistance mode, shorting the leads together does not result in continuity less than one ohm, the leads or meter are faulty.
 

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Your description might indicate that you have a solenoid not working. It might be electrically sound but stuck open or closed. If you had an electrical problem including a failed wheel sensor the computer would know and turn the unit off. If you had a wheel speed sensor out the tire control(flat tire monitor) would become inactive at minimum, but sure as anything the DSC and ABS would turn off and you would have lights galore.


To check a diode you set a meter to ohm's lowest is easiest although starting on the highest range and working down might be safer. The gist is on ohms connect one lead to one side the other to the other side and read. It will be a reading that is not 0 then switch the leads and do it again, the other way should be 0. Depending on your luck it could be the opposite. A diode will let electricity through one way only. Since your meter tests ohms by sending the electricity through the circuit from the meter battery, you will get a reading in one direction but if the diode is working it will block the electricity the other direction.
 

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To be clear, my last post is describing how I assume your meter should present a diode indication. Sailor24 is describing how to use the resistance function to check a diode which is what I was alluding to in my post before last and is what I recommend doing.
 

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You are correct to use the diode setting on your multimeter. If it has a maximum function even better, it will the show the max voltage over a period of time. Spin the wheel as fast as you can to get the readout.
But...... I believe this is all a waste of time. As said before, if you don't have trifecta lights, tire control inactive, and correspsonding fault codes, then your WSS ABS DSC system is working and you have a mechanical issue.
Be especially careful working at the DSC connector. Never put a testing wire or probe into the small square hole, you will ruin the female connector for the pins and have to replace.
 

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Discussion Starter #47
I just did a resistance test with audio on all four sensors at the female sensor connection. No reading or sound with the test probes reversed or not. I had the meter set to Ohms, the lowest setting. All four sensors seem to be dead.


I will have to deal with a bad male wheel sensor connector at the left front wheel. It was so brittle that it cracked into small pieces until I was able to pull what was left of the terminal body out. The female portion all seem to be fine. I might be able to reuse this and reseal it. I will apply a coating of non-conductive electrical grease when I install the new sensors.



I will now run Rheingold (ISTA+) BMW testing software to check for codes. Right now, all four wheel speed sensors and the large connector at the ABS/DSC unit are disconnected. Codes came up as expected:


S0018 No Communication with traction control system
000075 DME: Servotronic: no roadspeed signal
000084 DME: CAN timeout DSC
00008B DME: Interruption, Tempomat operation


These codes were cleared. After all other work is completed, I will recheck.



My meter is a rather new Klein Tools MM1000, with new batteries, leads in great condition. When I touch the leads together, I get a small reading and the buzz sound.


In a few days, the new sensors should arrive. They will be tested for continuity.


Big Thanks for following this thread and providing help!!!
 

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Discussion Starter #48
Today, front calipers are rebuilt. New pistons, seals, boots, guide rods and bronze guide rod bushings.


Tomorrow the rear calipers get the treatment.


Any suggestions for bleeding the master cylinder in the car that works? I would rather not mess with removing the MC to do a bench bleed. I bench bled it twice and I am not sure if all the air got out. I want to get this right this time around. I will do a web search on this...
 

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Glad I found this thread, as I'm experiencing VERY similar issues with the 2000 M5 that I just bought this week with a long, soft pedal, no improvement with bleeding, but also no warning lights. A question for you though, perhaps the strangest symptom that I'm experiencing is that the pedal is actually very firm and difficult to push while I'm trying to bleed the brakes, even with the caliper nipple open! Happily though, I actually have an extra ABS unit, albeit with a bad controller, but I'm just going to pull the hydraulic unit off the back of it and try swapping that out tomorrow to see if it improves matters.
So MAJOR success on my side! Indeed turned out to be the hydraulic unit half of the ABS system! I was able to determine this conclusively after I got plugged in with INPA. While cycling all of the ABS valves, got to the left-rear outlet and. . . no clicking!!! Removed the electronic front part and hooked it up to my spare unit and ran through everything again and all valves clicked properly, so then I went ahead and opened the lines, swapped in the good hydraulic unit, re-bled everything, and now brakes work properly again! Posting here in the hope this helps someone, key point being it was easy to hear which valve was non-functioning when cycling all of them in INPA!
 

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Discussion Starter #50
HAPPY HOLIDAYS m5board!!!!

My kids are grown and live out of state so Xmas is quiet here now. We will be all meeting up in Virginia in a few days for my 70th birthday at a fine Three Star Michelin restaurant outside DC.

Life is good!


austrianvespaguy,

Good news that you got your Beast up and running right. Nice having a spare part to swap in.
When I ran both INPA and ISTA+ software, I could hear all the clicks and pump action so I don't think ABS/DSC unit is at fault. I am still waiting to receive the new wheel speed sensors (next week).

I included some pix of the MC.


Yesterday after getting the rear calipers rebuilt and installed and all calipers bled, I decided to take another look at the Master Cylinder (bleeding). I really wish BMW designed in a easily accessible bleed screw on the MC. There is not much space to reach the metal tube fittings (what were they thinking?). With the MC in the car, I was able to install bleed fittings on the port facing the drivers side and the port at the front end with hoses to the reservoir. When I pumped, I did see air bubbles and then none. I pumped, pumped and pumped many times. I wanted to be sure air is out. Then I did another power bleed of the calipers. With the car up on a lift, I pumped the brake pedal and held it, started the engine and I could push the pedal way down. Before I started the car, I could slightly move the calipers slightly left and right. After running the engine and working the brake pedal, there is no side to side play. There is some clamp up, but the pedal moves too far down. If there is STILL air in the system, I don't know where.


Still a problem somewhere...


I am looking for an answers to these questions on bleeding a Master Cylinder.

1. The M5 MC has three ports. Do I put bleeding kit fittings on all three ports and run all three hoses up into the reservoir and then slow pump the MC cycling the fluid around and any air out? My MC is brand new OEM $$$.


2. If this is done in a vice (bench bleed), doesn't air get in once the bleed kit fittings are removed? How much time do I have to hook up the metal tubes, or that is not an issue?

3. There is so little room to access the MC mounting nut on the passenger side of the MC, I had to have the reservoir removed. More time and major PITA! None of my web searches showed removing and replacing the MC and Booster as a unit and if ports are open, is fluid running out and air getting in?

IF I decide to remove the MC and the Booster as an assembly, how do I keep air out until this is reinstalled? I think it would take me fifteen or more minutes to position this and reconnect the metal tubes. There is not much room in there!!!

Long post, but I hope to get some answers and advice.

Thanks!!!!!!!!!!!!!!!
 

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The main reason for doing a bench bleed for a MC is to pre lube it. A little air being in it does not really matter, it will either come out the top on the return or go down on the push.
Don't waste time trying to bleed it in the car, it is pointless.
 

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Discussion Starter #52
Hey, I am back..... Great B-Day and New Years!!!!


Back to the issue at hand.


I received the front and rear wheel speed sensors (pulse generator sensor). I did the multi-meter test and got reading for each as opposed to no readings on the old sensors. They are now installed.



I did a gravity bleed at each caliper letting fluid drip for about twenty minutes each. Then I used INPA software to work the DSC valves, pumps, etc... without opening the bleed nipples. Then I hooked up the Motive Power Bleeder, and while running Rheingold (ISTA+) with the bleed nipple open and end of bleed hose submerged in brake fluid. I triggered the pre-charge pump and pump with a final five long brake pedal pumps. Did not see any bubbles in the bleed hose.


I then started the engine and pressed the brake pedal which felt a little better. With the engine still running, I could fast pump the pedal and get some shorter travel.


Tomorrow I will put the wheels back on and drive around. I will go to a deserted parking lot and exercise the ABS/DSC to see if that is now working as it should (rapid pulse the brakes) and not lock up the wheels. I believe someone here said to just drive the car and the brake feel should come back in time.



If anyone has comments, please feel free to put them forward.
Thanks!!!!



To be continued....
 

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Discussion Starter #53
I did a test drive this am. My first impression was that the pedal feel and pad bite was little better. Drove the the deserted parking lot and with DSC enabled, I did some hard braking and hard sharp turns that got the DSC light to go on and off a number of times. With tires squealing and the DSC light flashing, I assume that is working, maybe? Under hard braking and the tires complaining, I don't think the ABS was working. I did not feel the brake pulsing. Right now I will drive the car as is. I never drive with the DSC on as it has a low threshold and is annoying to me.


I will keep monitoring the pedal feel and report back if there is any change as I put more miles on. My guess is that the gravity bleed made some difference for me.


It seems that quite a number of M5 owners have had this issue at some point. Not sure if there are many possibilities to this and no one fix for all.


Thanks People for your many inputs. This is a great site!!!!!!!!
 

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And your pedal doesn't go to floor anymore I assume?
Strange the ABS isn't working. I would scan for codes out of curiosity. Also go try the ABS on a dirt road.
 

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Try setting up ista to activate the solenoids again and then use a hammer or alike and tap the hydraulic side of the ABS while the activations are going on. Might free up any stuck noids.
 

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Discussion Starter #56
xrviz & sailor24,


Thanks for the tips!!! I will do both tomorrow if all goes well time wise for me.


Yes, the brake pedal does not go so deep to the floor as before. I am glad to see/feel some improvement!!!


Happy New Year!!!!!!!!!!!!!!!!!!
 

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Discussion Starter #57
Update...


I took the beast for a drive yesterday. Did not turn off DSC. Did some hard straight line braking and found a grassy area where I could slide the car around left and right. I was able to pull the car down from 60 mph quite quickly and while on the grass the DSC light flickered a lot. When on the grass, I could not get a good wheel spinning tail out slide going. I assume the DSC is working. Later I used ISTA to work all of the valves, pumps and vents. I could hear all the clicks, pump noises, etc... with each device activation, so again, I assume that is working too.


Thinking this issue through:


1. The MC fluid volume that is moved in relation to the pedal travel is a fixed amount.

2. The caliper piston(s) and pad(s) travel to contact the rotors is quite short.
3. As the pedal travels closer to the floor (which it still does), where does the fluid volume go?
4. Can there still be a large air bubble hiding somewhere that refuses to expel while bleeding the brake system?


My ongoing concern is even though I can bring the car to a quick stop, it is the amount of pedal travel I have. My Porsche 1996 993 and Ford 2003 F-250 does not have anywhere the pedal travel that the M5 has now and in the past did not have.


There must be something I am missing...


I will continue to drive the car and get some miles on it and do a code scan to see/fix anything that may show up.


Thanks Everyone!!!!
 

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Discussion Starter #60
My brain cells have been working overtime and keeping me awake at night...


Since my brake pedal goes way down to the floor, it appears to me, that there must be air hiding somewhere in the system. I decided to approach the bleeding process from a different direction that I saw on the internet. I am tired of pushing good, expensive brake fluid through the system and toss it out. What I tried is to run a plastic tube from the bleed nipple up to the MC reservoir and by pumping the brake pedal, push the fluid, and hopefully any air to expel at the reservoir. I raised the front of the up in the air, ran tubes from both front caliper nipples to the reservoir. Had both nipples open some and pumped the pedal with a slow pedal return. I could observe the clear tube and watch till no air bubbles passed by. I must have pumped the pedal seventy five times. Then I raised the rear of the car and did the same separately (left and then right) until no bubbles were seen. I did see some very small bubbles pass by while doing the front calipers and some larger bubbles from the rear. At this point I thought I was near the fix on this. However, upon starting the engine and pressing the pedal, it again went way down.


Later today I remounted the wheels and drove to a secluded place where I could test the DSC and ABS on grass and gravel road. Under hard acceleration and sharp turns the DSC light would light up. Hard braking on the gravel road did engage the ABS where I could feel the pulses. I did notice under the hard braking, when the car was almost stopped, with my foot still hard on the pedal, the pedal would drop lower maybe an inch or so. I repeated this several times with the same pedal drop. Is that normal???


So, yes the pedal seems to go way too far down to the floor.


I wonder if someone could take some measurements of their range of brake pedal travel for me to compare mine to? I used a tape measure with large numbers. With the edge of the tape resting on the top edge of the pedal and the end of the tape at almost right angles to the inclined section of the floorboard behind the pedals. I could lean over to the left and see the measurement to the front surface where the foot touches the pedal. I got measurements with engine off, the point where I could feel the booster is, and under full on foot pressure. Then with the engine running where the pedal ends with full on foot pressure.


After I took the measurements, with the engine off, I was able to push the pedal to the floor (3-1/2"). I let it return and pushed again, this time I measured 4-1/2" (some pump up), and again to 4" (no pump up), one more time all the way down to 3-1/2". Not sure what that means. I will read over the Vehicle Brake Information that xrviz provided and see if something clicks for me.


There is no slop in any of the caliper mounts, the calipers (just rebuilt), braided lines, new pads, new master cylinder. If the booster was bad, it would just make applying pressure harder. With the engine running, I can depress the pedal quite easily. It is when I apply firm, constant pressure, the pedal goes way down.


I don't like losing sleep over this but it is driving me totally nuts!!!!


Long Post but thanks for the input!!!!!
 
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