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Discussion Starter #1
So; it was a few weeks back when my car beeped, and I saw the dreaded "bi-fecta" (brake and abs lights lit; amber). When I restarted the car, they were gone, but the problem did come back a few days later.

I got under the car, and cleaned off all four wheel speed sensors. There were some minor whiskers, but I've seen much worse (on other cars).

Problem did not re-appear for several weeks.

Now it's back, and it does not go away when I shut off the motor. It comes back as soon as I start it up again. Therefore: It's a real problem :(, and cleaning my wheel speed sensors did not fix it.

I plugged in my old trusty bmw scanner 1.4.0, and these are the codes I got.

5e18[24088] CAN DME/DDE data not plausible
5e19[24089] CAN DME/DDE engine torque not adjustable
5e1A[24090] CAN DME/DDE Signal Error
5e24[24100] pressure sensor 1/2 not plausible
5e21[24097] Pressure Sensor 2 electrical faulty

I googled, and found a few hits that say I have to replace this part. Brake pressure sensor - (maybe two of them): 34521164458 - the DIY's indicate I'll need an 11mm flare wrench and a 27mm open-end. (yay, new tools!).http://s1.e46fanatics.com/forum/images/smilies/excited.gif

So my questions are:
1) to those who know; is this a correct diagnosis?
2) Do they really cost $160 per sensor? Or can I get away with the $35 one I see on Amazon?
3) Will I need to flush all of my brake fluid, or should I be able to get away with just bleeding after?
 

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Discussion Starter #3
yeah, connection's not broken or loose as far as I can tell.

This makes for three weird/intermittent electronic gremlins now: oil level sensor, coolant level sensor, and now brake pressure sensor(s). . . .
 

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Discussion Starter #5
I wanted to follow-up on this.

Looking at my MC and BPS's, I can't even get my hands down there to TOUCH the electrical connectors. They look. . . erm. . . connected. My bay is pretty clean and everything is in pretty good shape; trying to research this I don't really see a procedure for testing the sensor in-situ.

Even if I pull the compartment shield, and move the wire harness out of the way, I can't get anywhere near that sensor or connector with my hands.

The procedure talks about disconnecting the brake booster hose. My booster has the check valve sitting right up against the booster, then the hose connects to the check valve, and it's got one of those single-use clamps on it, so I can't unclamp it - do I just pry the check-valve off the brake booster to disconnect it? Or do I have to cut the clamp and install a new one when I put it back? Even then, I'm not sure I can access that sensor. If I could remove the plastic box full of all the electrical connectors and the controller, then this job would be much easier.

Last week, I power-flushed my brake fluid. If anything, it seems to make this problem worse (less intermittent. Lights come on almost every time I drive now). This convinces me that one or both sensors is bad.

If anyone has any tips on this procedure, that would be helpful.
 

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// Quandt AG (Retired) //
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Not sure what version ABS you have. You should check as e46's came with different Bosch ABS systems. The pic below is a pressure sensor out of the e46 DSC 5.7 unit. There is only one that screws into the side of the ABS unit.

In looking at your errors it does appear to be a pressure sensor error. Good news is you don't have an error for a dead ABS unit.

The pressure sensor has a tiny pin hole at the tapered end that screws into the unit.(Second pic) Wouldn't take much to clog that. You could try removing it and flushing out the sensor. Gotta think there are a bunch of these sensors floating around on the used parts circuit. I have two I saved from failed ABS units.

Edit: before you replace anything do check the harness is connected properly and the wiring is intact - the pressure sensor will have it's own connector.
 

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Discussion Starter #7
So; mine looks exactly like the diagram in this procedure:
https://autotecdirect.wordpress.com/2012/04/25/bmw-e46-dsc-pressure-sensor-replacement/

I think this means I have the MK 60 DSC.

My Master Cylinder has two of these screwed in; the ABS unit, is down below in the same compartment, and I don't see any pressure sensors attached to the ABS unit.

I connected INPA on my laptop, and read the DSC (analog) as I exercised the brakes. The #1 sensor sits at about "-1.30" (don't know what the units are), and the #2 sensor sits at about "16.50"-ish (they both fluctuate constantly, even when there's no pressure on the pedal). The #1 sensor maxes out at about 110, and the #2 sensor maxes out at about 130?. Each sensor also has an "offset" meter, to the right, on the INPA screen. The #1 offset is in the middle of the green zone. The #2 sensor offset is about 3/4 of the way to the right side, and it's in the red zone. I guess that confirms that there's some problem with the sensor - but maybe it's intermittent? When I cleared the codes, the same codes came right back. When I drove it with INPA connected, the "bi fecta" warning came up on the dash, with the beep, and at the same time I was monitoring the analog DSC pressure sensors with INPA, and the pressure sensors were behaving pretty much the same as when the car was parked (same range). So I didn't see #2 drop out or anything when the bi fecta beep happened.

I'm not going to back-out the old (bad) #2 sensor until I can get a new one shipped to me.
 

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Discussion Starter #9
I think I fixed it!

The replacement sensor came in, from ECS Tuning ($140). I didn't want to chance a cheapo ebay sensor, or just flushing out my current sensor, because frankly, getting AT the thing was kind of a pain in the keister. (as you'll see in my pics). I don't know if other models are as difficult. What I ended up doing:

1. removed strut brace (as always).:thanks:
2. removed cabin air filter tray (as always).:thanks:
3. removed the shield between the master-cylinder compartment and engine compartment.
4. disconnected battery, and all connectors in the DME box, so I could move the harnesses out of the way. I thought I'd be able to remove the plastic box that holds the DME, because, it was just really impossible to reach the master cylinder with it there, but the wire harness is threaded through this box, so there's no removing it without unspooling the whole fricking thing. :banghead:
small_20161001_123646.jpg
5. disconnected brake booster hose at grommet.:eek:
6. drained master-cylinder reservoir of fluid. (sad, because I JUST flushed it).:bawling:
7. stuffed the area under the master cylinder with paper towels, to prevent brake fluid from running all over the place.
small_20161001_134947.jpg
8. had to disconnect both hard brake lines from master cylinder.
9. Could not get my hands on the connector. Had to gently work it off with a very long screwdriver and needlenose pliers. Due to inconsiderate automotive engineers.:ben:
10. Could not get my brand new 27/30mm offset wrench anywhere near the sensor because: inconsiderate engineers. :banghead:
11. Used an adjustable pipe wrench to loosen the pressure sensor. Like a peasant.:idea:

There was some crud in the old sensor that I flushed-out with brake cleaner. I am keeping the old sensor in case I need a spare; but this seems like it may be a viable way to recycle these? The problem is not paying for a new sensor. The problem is the amount of brake fluid you have to replace, and the fact that it's so hard to even get at the sensor to even try to test the connections, when you can see it with your eyes.
small_20161001_140032.jpg
small_20161001_140106.jpg
12. re-assembly was reverse of disassembly.
13. Bled brakes with motiv bleeder, and fresh ATE fluid. :str8pimpi
14. Checked new sensor with INPA. Cleared codes.:thumbsup:
small_dsc-sensors-pedal-off.png
small_dsc-sensors.png
15. I also cycled the ABS unit using INPA. I'm not sure I did this right, so I"m not going to post instructions, but everything seems to be working fine now, so I guess I didn't break anything. :loco:

Problem seems to be gone now! :clap:

Note above screen captures from INPA:
To get there, I ran INPA, connected with the cable to the car's computer.
SHIFT+F6 selects "older BMW models" :facepalm:
Then I picked "e46 chassis", then "dsc mk60" (different depending on your model)
F5 to Read Status
F1 to Read Status Analog
F2 to Read DSC Sensors

You get these images, and the pressure sensors are "Print brake circuit 1" and "Print brake circuit 2". You can see them fluctuate when you push down on the pedal. My "old" #2 sensor (the one in the FRONT of the master cylinder is #2) was changing values even when no pressure was applied. Actually, they BOTH were, but #2 was way worse. The Old #2 also had different values than the Old #1. After I put the New #2 in, the two sensors agreed with each other more closely.
Also, the "offset" values on the right side are now in-agreement.

The NEW #2 sensor's values are a lot more stable (when no pressure is applied). They blinked-around a little bit but not very much.

When I cleared the codes, the bifecta lights were gone, and everything seemed to work fine.

In retrospect, I am wishing I had also removed the #1 sensor and flushed it out, as long as I had the brake fluid reservoir empty.
 

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// Quandt AG (Retired) //
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Great job Tristero -

Just goes to show the power of Diagnosis & Repair

You didn't have to re-calibrate the Steering Angle Sensor (SAS) since your core ABS/DSC unit was not swapped so the SAS value remains valid.

Anyone reading this thread with similar issues - notice the importance of having INPA to diagnose/repair e46 ABS/DSC units (a component of the software package: BMW Standard Tools)
 

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I want to thank the OP for diagnosing this, but for the benefit of future readers, I think there is a better way to replace these sensors

Simply unbolt the master cylinder, move it about 2 inches toward engine and then remove/replace sensors with a deep 27 mm socket. Don't disconnect brake lines or drain brake fluid out of reservoir, but plan on bleeding brakes afterwards because some fluid will escape (an air enter) when you swap a sensor. 50's kid did an excellent video on this linked below. Replacing sensors is discussed in the first half of the video.

https://youtu.be/CvyVCwCAx1Q

This is what i intend to do to replace a brake sensor.

My symptoms:
'05 330Cic ZHP w/125k miles.
pulled out of winter storage (6 months) about a week ago

-Yellow DSC triangle and yellow brake light are on (2-lights)
-Scanning with INPA/PA Soft i get code 5E21 - Brake Pressure sensor #2 - Electrical Fault
- I can clear the error code /lights in INPA, but I comes back after 15-20 mins of driving.
- If I measure live data in INPA i see that Brake pressure #2 is showing 10-15 bar pressure higher than #1...about 15 bar at idle without touching brake pedal

I think I have a bad pressure sensor or one that is clogged with debris.

I will report back after I replace sensor.
 

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Looking forward to the successful resolution here.
 

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I want to thank the OP for diagnosing this, but for the benefit of future readers, I think there is a better way to replace these sensors

Simply unbolt the master cylinder, move it about 2 inches toward engine and then remove/replace sensors with a deep 27 mm socket. Don't disconnect brake lines or drain brake fluid out of reservoir, but plan on bleeding brakes afterwards because some fluid will escape (an air enter) when you swap a sensor. 50's kid did an excellent video on this linked below. Replacing sensors is discussed in the first half of the video.

https://youtu.be/CvyVCwCAx1Q

This is what i intend to do to replace a brake sensor.

My symptoms:
'05 330Cic ZHP w/125k miles.

-Yellow DSC triangle and yellow brake light are on (2-lights)
-Scanning with INPA/PA Soft i get code 5E21 - Brake Pressure sensor #2 - Electrical Fault
- I can clear the error code /lights in INPA, but I comes back after 15-20 mins of driving.
- If I measure live data in INPA i see that Brake pressure #2 is showing 10-15 bar pressure higher than #1...about 15 bar at idle without touching brake pedal

I think I have a bad pressure sensor or one that is clogged with debris.

I will report back after I replace sensor.
I also just replaced quick (once loosed, removed with left hand, swapped with right), spilling a bit of brake fluid, and not drain reservoir, when I replaced one of sensors. cycled ABS/DSC with schwaben, bled all corners
 

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As follow-up

My DSC + yellow brake lights (2 lights) went away on their own without clearing codes -although I had cleared codes previously.

Now, when I look at live data in INPA: E46 - Chassis - DSC Mk60 - Read Status- Live Data Analog - View DSC Sensors
I see that brake pressure sensor 1 & 2 have Bar pressure values much closer to one another when car is running before and after I press on the brake pedal...

I have now had several driving cycles over the last several days with no return of the errors/lights

The errors occurred in the seven days after pulling the car out of a 6-month storage. It may have been that I had some debris in the brake fluid that got suck in a sensor. Once again, these cars really like to be driven.

I did source a complete used OEM master cylinder with OEM sensors for $25 which I will have on hand if I do need to replace them in the future. New Genuine OE sensors (made by ATE) would have been $160+ each, aftermarket sensors are $35+ ea, but I figured used OE would probably keep me going for several years if I did have a bad sensor.

Given no errors currently, I will hold off on replacing any sensors for the time being. Although I will take this opportunity to flush/bleed my brake fluid which is WAY overdue.
 

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Subd because I got 5E21 and 5E26 the other day. I replaced my MC and BB about 1000 miles ago and of course flushed the fluid.

Questions

1. What~s the consensus on replacing both pressure sensors even if only one has given an error?

2. 5E26 is Control unit voltage supply sensors - error. I searched for this specific error but couldn~t find any info on it. Any help on that is appreciated

3. Are these codes definitive? Or is there some way to check sensor 2 for to make sure? 50sKid did an Ohm test but that didn~t seem to show a fault.
 

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Questions

1. What~s the consensus on replacing both pressure sensors even if only one has given an error?

2. 5E26 is Control unit voltage supply sensors - error. I searched for this specific error but couldn~t find any info on it. Any help on that is appreciated

3. Are these codes definitive? Or is there some way to check sensor 2 for to make sure? 50sKid did an Ohm test but that didn~t seem to show a fault.
1.. I thought long and hard about this...There are several people who did replace them both. But these forums are not overrun with stories of bad brake pressure sensors. I was planning to replace just one sensor. It was my hope that by just removing the MC without draining fluid this job would be pretty easy, and I wouldn't mind going in a second time if a second switch failed.

2. Have another search..I found this - which was fixed by replacing Yaw sensor.
https://forum.e46fanatics.com/showthread.php?t=933040

3. No, they not definitive..50's kid had at least two codes, 5E21 & others. I had JUST 5E21... When 5E21 is the only code it is very likely related to pressure sensors. When 5E21 is combined with other DSC/ABS codes, it may be something else. i would suggest you get INPA running, or find someone who does, and look at both brake pressure sensor readings in live data. It helped me identify my issue..Which went away on its own....
 

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1.. I thought long and hard about this...There are several people who did replace them both. But these forums are not overrun with stories of bad brake pressure sensors. I was planning to replace just one sensor. It was my hope that by just removing the MC without draining fluid this job would be pretty easy, and I wouldn't mind going in a second time if a second switch failed.

2. Have another search..I found this - which was fixed by replacing Yaw sensor.
https://forum.e46fanatics.com/showthread.php?t=933040

3. No, they not definitive..50's kid had at least two codes, 5E21 & others. I had JUST 5E21... When 5E21 is the only code it is very likely related to pressure sensors. When 5E21 is combined with other DSC/ABS codes, it may be something else. i would suggest you get INPA running, or find someone who does, and look at both brake pressure sensor readings in live data. It helped me identify my issue..Which went away on its own....


Thanks for the answers!

1. I agree. I don’t think it would be hard to go in a second time since the sensors aren’t cheap.

2. I hope it’s not my yaw sensor. Drummr8 wrote it was a pain to get to. Plus I don’t like installing used sensors. :/

3. I have INPA. That’s on my list to do today.
 
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