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Brake Pressure Sensor (DSC/ABS/BRAKE Trifecta)

245K views 74 replies 21 participants last post by  mattmar1 
#1 ·
Ive spent about 12hours pouring throught the mounds of the ABS/DSC/Brake trifetca issues for a week and havent found any good DIY on Brake Pressure Sensor testing.

If anyone can point me to a DIY thread for Brake Pressure sensor testing, please do so, however I coultnt find any specifics from bluebee or 540iman that specify a process.

I have an 02 E39 with the ABS/DSC/Brake light issue for about 6 months however speedo and cruise work fine. I have not heard of anyone having this specific issue, but all 3 lights usually pop on for me 3/4 the time when Im braking at a stoplight, (light sometimes turns off/on while brake pedal down) which leads me to think its the brake pressure sensor (vs ABS module or speed sensors.) The other 1/4 is during normal driving.

I did the "BlueBee wheel sensor diode test" which did show failure in the RR, however my LR diode test was only working when I reversed the leads. Im still questioning this test vs the gold standard which would be to actively measure the sqaure voltage output of each, however I havent the time or equipment to do this. Despite my DMM diode function working, I cant get any Ohm readings. All sensors have been pulled and cleaned, still with trifecta issue.

BRAKE PRESSURE SENSOR TESTS

There are 3 wires in the rear of the sensor. After much testing I came to this conclusion.
-blue/black (ground)
-purple/black (+5V)
-white/blue -variable voltage per psi

SENSOR TEST
To test the sensor output with DMM, ground the (-) probe, and tap the (+) probe into the blue/white wire, turn key on and meausre voltage change with brake pressure.

Despite 0 -> full brake force, I could only get a 0.2V increase from .69V to about .89V. The other wires were a constant. I have read the voltage should approach over 4V at maximum pressure.
Does anyone have specs on the resistance through this sensor?
Is there a pin from the ABS pinout that corresponds to this wire for testing?

CONCLUSION
It appears my brake sensor is the likely culprit here, however I am still not convinced I dont have a bad wheel sensor or ABS module, although all speedo and cruise controls work fine.
I have heard of erroneous diode testing even thought the wheel sensors are normal....
And I am not sure why when I do the diode tests at the actual rear sensors, they are all faulty with OL/OL. I am also perplexed why my LR diode polarity is opposite the other 3 (verified this 5 times), as this could possibly mean a faulty ABS module? :dunno:
I'll probably finally load up GTI and INPA for more data, as Ive been meaning to do this, As for now its nice to do peel-outs with the DSC failing :D

Any thoughts appreciated!
Sorry to post yet another 1000+ thread on the trifecta of death.

-James
 
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#41 ·
Hello!

I currently have a brake pressure sensor fault on my DSC module, its intermittent at the moment so I purchased a spare DSC module so I could investigate further. The replacement module was fault too but these were simple blown MOSFET issues (Faults with return pump and pre-charge pump) I have fixed this now and documented what I found on a new thread in the E65 section.

However while I was in there I documented the wire bond connections, and which pins they go to to see if any of the common failures can be contributed by the stiffer aluminium bond wires.

I numbered the gold bond pads 1 to 45, please excuse my repair at the left!



I did not manage to identify all of the connections entirely but I think 90% is there, here is the list:



I believe this is the same unit as used in the E39 but uses a slightly different pinout? i.e. the direct diagnostic interface is not used on the E65/66 pin 11 of the main connector but is on the E39.

Interesting that the DSC pressure sensor has an alluminium bond wire for its GND, I bet this is whats up with mine and other posted before. I wonder if grounding the sensor elsewhere will fix the issue? I may give that a go!

I will cut mine open and see if I can confirm a poor connection on the bond pad I have numbered 37.

Stuart
 
#42 · (Edited)
I will cut mine open and see if I can confirm a poor connection on the bond pad I have numbered 37
Thank you very much for reporting this helpful information!

You take fantastic pictures!


Probably it's best to put this excellent bondpad-pinout information in the canonical thread for repairing the ABS control module:
- How to physically test & repair the Bosch ABS control module (1)

I believe this is the same unit as used in the E39 but uses a slightly different pinout? i.e. the direct diagnostic interface is not used on the E65/66 pin 11 of the main connector but is on the E39.
As for whether your vehicle uses the same Bosch ABS control module as ours, this thread has a chart which only goes to 2003, but which shows that the 2002/2003 E65 does use the same lousy ABS control module that we have on the newer E39s.
- How to diagnose the BMW amber ABS BRAKE DSC/ASC trifecta or bifecta (1)

Your bondpad pinout chart is an excellent addition, because I don't think we've characterized the pinout on the line of bondpads inside the ABS control module yet; we've only characterized the pinout on the harness connector:
 

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#43 ·
Hello bluebee,

Thanks for the reply, not a problem, I came across this thread when I was researching so figured I would try and contribute some information to help you guys out.

I understand the later E39 used the same Bosch 5.7 unit as used in my E65, however I believe they are wired slightly differently and will almost definitely have different software.

I have compared the pinouts using the BMW WDS to see the differences, the E39 had a diagnostic interface at pin 11 of the connector, that's not used in the E65 as all communication takes place over the PT-CAN. Also the E65 does not have a hard wired DSC button input, this again is controlled via PT-CAN because the option is selectable in the idrive menu.

Interesting that it's a particular bond that comes off, this gives you wheel sensor errors reading through the post. That wire you mention is indeed one of the 8 connections that connect to the four speed sensors.

I hope to update later in the week with findings of my DSC module and the brake pressure sensor fault.

Stuart
 
#44 ·
figured I would try and contribute some information to help you guys out.
I love your attitude!
We NEED help, as we've never had a pinout before, for the 45 pins of the ABS control module, for example.

Personally, I believe that we can fix the bad epoxy connection at pin 7 ourselves, for almost nothing, which is why all the information you can provide is great.

I especially LOVE your pictures. Very clear. Very focused. Very nice!

I think what happens is that the particular bond intermittently fails, due to heat/vibration/whatever, and, since it's a duplicate, the voltage drop across the failed bond changes, which screws with the head of the abs computer, which is why all sorts of odd results come out of it, such as an indication of a failed BPS, which often, if not always, turns out to be false (ask me how I know).

So that others benefit, here, for the record, is your post on the 7-series forum, for the folks here to benefit from, now, and long after we're gone.

[/QUOTE]
> 7 Series - E65 / E66 (2002 - 2008) > Bosch DSC 5.7 ABS Module Diagnosis and Repair
Well, I have been having a bit of fun with my faulty ABS/DSC module over the last couple of weeks.

I thought I would share my expereineces with you so you can have a go at fault finding and repairing some of the common faults yourself before sending it off for re-manufacture.

If your lucky, you can repair these units pretty easily for under $20! :D

If you have some patients, and a very steady hand! its possible to repair some of the internals if you are very careful!

There are a couple of common faults with these units that I will detail and show how to repair, you will need some basic electrical understanding, some idea of how the DSC system works and of course a code scanner, INPA is my favourite! ;)

Error Code 5E9B - Return Pump

Symptom - The pump fitted to the rear of the DSC hydraulic unit runs continuously, even with the ignition off, this causes a flat battery.

Cause - The MOSFET drivers for the return pump are damaged and one or both of them are short circuit.

Error Code 5EE4 - Pre-charging Pump

Cause - The DSC unit has detected a fault with one or both of the internal MOSFET drivers and will no longer drive the pre-charge pump.

Both of these faults will cause all three of the ABS, DSC and Traction Control lamps to illuminate.

The return pump is driven by two MOSFETS located on one of the heatsinks shown below:

The devices in the image below, on the right hand side, are responsible for driving the return pump, they work in parallel, you can clearly see the discolouration to the screws on the right heatsink, this indicated the heatsink got VERY hot!

One or both of these devices will be short circuit, this is what causes the return pump to run continuously.

The devices on the left have a different function, the other MOSFET on the left side actually switches the DSC module on and off, this is done by the T15 wake up signal that is required for modules on the PT-CAN.

The schottky diode package, next to the MOSFET, basically connects the two separate power supplies to the DSC module from two different fuses (for safety) i.e. if a fuse blows the DSC module can still have limited functionality using the second supply to report faults to the driver. Simply check the device with a multimeter using the diode function, or change it if unsure, its unlikely that it will be damaged. Again if the DSC module communicates and powers up then the MOSFET can be considered good too.

The legs of the devices are formed at 90 degrees and then spot welded to the support assembly that carries the conductors. These can be carefully snipped off and replacements soldered in place.

The devices fitted to my DSC module were STP60NS04ZB, they are no longer available, the general spec is as follows:

60A N-Channel MOSFET, the voltage is clamped.

I used 50V 100A N-Channel MOSFETS, try and get something with a low on resistance and somewhere around 50-100V 70-100A, this will be sufficient, cost of components is under $20.

Re-assemble the DSC module and try it in your car, this should now fix the constant running of the return pump. :thumb up:

Right....

The pre-charge pump is a little more tricky! The MOSFETS for this pump are inside the cover of the electronics module, this has to be carefully cut open :yikes:

This is the delicate part of the unit, it has a ceramic substrate circuit that has wire bonds and is sealed under a transparent silicone type goo!

I don't have a photo before I started and I don't want to rip-off other peoples photos so I will dive straight in!

Once the lid is removed, the two MOSFET devices are located to the side of the main circuit on a separate ceramic substrate.

You can see clearly that the device on the right is damaged, and you can see the damaged/melted silicon. this is effectively whats inside the black devices used for the return pump, why on earth they thought putting them inside like this in bare die form is anyones guess :dunno:

Anyway, you will notice the wires are silver coloured, they are in fact aluminium and welded to the gold bond pads and die.

Unfortunately we cannot solder to aluminium, but we can solder to the gold pads and the edges of the components on the main circuit.

Here is a rough hand drawn schematic of how the two MOSFETS drive the pump:

As you can see, the die on the left switches the pump to ground/0V and the device on the right switches 12V to the pump. You will also notice two feedback inputs, this is how the DSC monitors the MOSFETS to determine if they are open or short circuit.

The damaged die measured 41 ohms, the DSC can see that the feedback input is at 12V even when its not switching the MOSFET on so reports the fault.

I managed to repair the module by fitting another N-Channel MOSFET inside the DSC module itself, its not pretty, but it works!

The green wire connects to the GATE of the MOSFET, this is the signal from the DSC to switch it on, the black wire is the feedback to the circuit for diagnosis. This has to be carefully soldered to the side of the capacitor.

Note: it takes a fair amount of heat to solder the gate wire to the gold bond pad, this is because its thermally connected to aluminium heatsink under the ceramic substrates. Its a bit fiddly but its possible to repair if your patient!

BE CAREFUL NOT TO DISTURB THE GOLD WIRE BONDS, THEY ARE THINNER THAN A HUMAN HAIR AND INCREDIBLY DIFFICULT TO REPAIR WITH SOLDER!

Hope this helps someone else!!!

Feel free to ask questions, I will list the wire bond pinouts for reference as some come loose internally through temperature cycling and cause all sorts of faults, the aluminium bonds are the most common to break, and can be soldered with wire with patients! thats another post though! :)

Stuart
 
#45 ·
No problem bluebee, I'm glad to help. I enjoy reverse engineering things like this out of curiosity, it's nice to pass the information on to others that are interested.

Yes your exactly right, the environment I.e. Temperature cycling, vibration etc... Are the major factors here.

The 42 pins of the main connector don't all connect to the ceramic substrate inside, some connect to the discreet components in the rear of the module.

Please bear in mind where I have stated 'not used' that means it's not used in the E65, the E39 will be different.

I will take some better pics of my old DSC unit next week under a high power microscope, hopefully I may be able to identify a dodgy bond wire visually.

Stuart
 
#46 ·
Quick Update:

I cut open my old DSC module today to inspect the wire bonds in an attempt to trace the cause of the pressure sensor fault.

I have started inspecting areas around the wire bonds, I'm convinced some appear to show cracking around the edges. Problem is, the silicone type sealing "goo" has a very uneven surface and its making it difficult to focus in some areas.

Before I go poking around, I will measure the resistance of the wire bonds from the substrate to the housing bond pad, I will do this at ambient temperature, and at around -10 degrees celsius.

I had been experiencing the fault regularly in the colder weather here in the UK, -10 should just about do it I hope! :D

Anyway, if anyone is a little geeky like me :eeps: I have taken a few photos of some of the devices inside the unit.

One of the two main processor dies:


Closeup of 'Die' markings:


Markings on the 'Die' show the processors are in fact Intel 88C196EC automotive grade 16 bit micro controllers.

Siemens propitiatory semiconductor device, mask dated 1994:



ST Microelectronics branded device, mask dated 1992?:



What looks like a 'Good' wire bond:



This one looks to have shadowing around the weld area, it's hard to determine wether this is a crack or not, the image isn't great. This wire bond is the voltage supply for the pressure sensor.



I will update again when I complete some of the resistance measurements and temperature tests.

Stuart
 
#48 ·
Based on this post in the canonical trifecta thread, I may have gotten the BPS pinout wrong in the descriptions of this thread ...
> E39 (1997 - 2003) > 2002 E39 ASC BRAKE ABS lights on => Diagnostic Procedure & Parts Location

Just wanted to share a video I recorded today. Long story short, I recently purchased a 740i with brake light trifecta and started diagnosing using inpa, found pressure sensor error.
Tested pressure sensor today and realized connector pins were actually 1:Ground 2:Signal 3:+5
Mine was not getting ground, it was getting +5 and I was able to trick ABS unit by grounding signal pin.
Used a cable to supply ground to the sensor then voila! It worked.
I was reading full pressure on INPA now it was at 0 and responding linearly to system pressure.
I was lucky, apparently broken jumper in the unit was for ground only.
I drove it home after this, and no more lights, no more codes in INPA either.

Below is the link to the video.
https://www.youtube.com/watch?v=xU72vLhmQTU
 
#49 ·
BTW, it bears repeating, just as we saw in the video above ... I have never seen, anecdotally anyway, in this forum, any bad brake pressure sensors, yet, we constantly see the ABS control module code 81 implicating a bad BPS when the ABS control module's 7th aluminum (duplicate) wire partially lifts off its gold bondpad (causing resistance and subsequent voltage changes to occur in the ABS control module).

As it even happened to me, I say this from my own experience also.
 
#50 ·
I was looking something up for someone with a brake problem when I ran across this nice Pelican DIY which has a picture of testing of the brake pressure sensor...
 

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#51 · (Edited)
I am experiencing the tri-fecta of lights on my dash, and suspect more likely than not the ABS Module. But today I just started my e66 and had the warning come on saying "before engaging gear press brake. When leaving the vehicle switch off the engine. Accident Hazzard. See dealer. Well, the car dives perfect, and it only says this error when you release foot pressure from brake pedal, not when pressed. Thanks for posting how to test the brake pressure switch, my abs module was only making it seem like it was the switch. You guys are awesome and bless others with knowledge .... next I'm sending abs module in for 95 bucks to bba for rebuild....
 
#64 ·
Another module, same code

So I received a second module from MM and installed/coded it. Lights were out for a couple days / 150+ miles but they have come back withe same code - 114 Pressure Sensor (Offset)

Thinking out load...

This bit is from the E46 but is part of the description of the Bosch DSC III 5.7 which is what my E39 has:

Brake Pressure Sensor (Bosch 5.7)
The brake pressure sensor is mounted on the
DSC hydraulic unit in the front axle circuit. The
sensor is provided with a 5V reference voltage
by the DSC control unit.
The sensor provides the control unit with an
analog signal proportional to brake pressure.
Voltage increases with increasing brake
pressure.
Plausibility with BLS
The signal input from the brake light switch is compared with the pressure sensor value.
The pressure sensor must not detect more that 5 bar when the BLS is not actuated.
Both signals are used to form a redundant BLS input which is monitored during all phases


This sounds like a plausible source of an "offset" as my lights always seem to come on when I am not pressing the brake. As a matter of fact I noticed today that the lights came on right after i released the brakes at a stop light.

The e39 doc does not specifically mention this redundancy. Is it possible that there is some extra programming that needs to happen? Is coding not enough? I doubt it but these modules were in many different vehicles.

So, possible culprits are:

A second bad module - not outside the realm of possibility but I give it a low probability since it is the same code (which may also mean my original module was ok)

Bad pressure sensor - sensor seems to work as I can see changes in INPA when pressing pedal etc. but it is possible

Electrical short (ground) - A short that is causing it appear like extra pressure.

Some mechanical reason that is actually producing intermittent extra pressure - Faulty hydro unit? Flaky charge pump? Could air in the system cause this?

Moar testing to come but any thoughts or insights are welcome :)
 
#70 ·
dsc pressure sensor line code

DSC pressure sensor line code. After replacing the DSC pressure sensor & pressure bleeding at all the wheels the same codes reappears after driving 5-10 miles & of course trifecta lights are on. Scanner data shows brake pressure increases as pedal is depressed. What is best suspect?
 
#71 ·
https://www.bimmerfest.com/forums/showthread.php?p=12990343#post12990343

Hope this goes to Dodd who had the question.
Reading your post, I see you have tried a lot of different approaches.What I do not see is a test of leads from/the ABS module to the pump pressure sensor. If your testing sees an increase in brake pressure, that mY still mean the ABS/ module is not "talking" to the brake pressure sensor. Taking a wire and a small pin or needle probe, test the voltage of the 3 wires. The other end of the probe should go to a ground. One is a ground, the other is 4-6 volts and the third is the sensor. As someone applies brake pressure, see if the voltage of the third wire increases from 0 to whatever. If there is no increase, the wires in the control module that connects the control module to the brake pressure sensor have desoldered. While you can try to repair these fine thread wires, I strongly recommend sending the module out for overhaul. Mine was $325 but that was sometime ago. You can find an overhauler on the internet. Mine was in Idaho or Oregon.
Hope this helps. :)
 
#74 ·
Hello,
I know this is an old thread but it's linked in many places as the reference for these issues and I wanted to add to it.

I bought a 2001 525iT with all three lights on. Following this thread/guide I bought a C310 scanner and got a code 51 Pressure Sensor, Line. I checked the live data for the sensor and it said 217bar with no pedal pressure.... Yikes. Pressing pedal didn't change it.

I checked the voltage at the connector and got 5v. I then checked the sensor wire and got 0.5v. I then checked everything again and couldn't get any voltage. I went straight to ground with my meter and got 5v again. Clearly the sensor ground is bad. I cut the shielding back and clamped an alligator clip to sensor ground and chassis and got voltage again. OBD showed 0bar with no pedal pressure, 14bar with pedal pressure and 28bar when car is running with pedal pressure. All the lights are gone, and ABS is functional.

Just wanted to post this incase it helps anyone else. Thank you to all in this thread for the information.
 
#75 ·
glad ya attacked it and got it fixed. well done.
just an fyi, while the creator will work for some readings, its inaccurate on others, and their support/updating is pretty much non existent. the one i bought years ago resides on my garage wall with a drywall screw run thru the display.
 
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