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Thread: False Brake Lining AND Brake Fluid warnings - LKM or what?

  1. #1
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    Question False Brake Lining AND Brake Fluid warnings - LKM or what?

    While driving my E38 the other day the Brake Fluid red light came on almost simultaneously with a Check Brake Linings message on the display. I wasn't even using the brakes!

    But it's got fluid between the Min and Max lines, and the sensors (left front and right rear) and wiring appear to be intact. The rear pads have about 20% left. I jumpered the rear wear sensor connector and the check linings message would not go away even after turning the key "on" for a while.

    Interestingly, when I pulled the connector off the master cyl reservoir switch, the Brake Fluid light stayed on and the display showed "Check Brake Fluid". I jumpered the pins and the cluster message went away, but not the red light.

    Are these warnings controlled by the LKM? The reason I ask is that a couple of years ago there was a bad sunroof leak that ran down into the LKM, which made my turn signals, headlights and other parts act very strangely. I pulled the module and found significant corrosion in several places. I cleaned it off carefully with a toothbrush dipped in 91% alcohol, distilled water rinse, and a gentle heating, reinstalled it and crossed my fingers. Everything worked perfectly again - until now...

    thanks
    Charles
    '98 740iL E38 201k, TCG at 190k, 5HP24 at 195k
    '97 540i/6 E39 Dinan blower & stage 1 suspension 114k
    '93 525i E34 "Golf Ball" (hail damaged) 334k

  2. #2
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    Nobody?

    I put new rear pads on today (they were getting thin, and the RR wear sensor was indeed touching the rotor). New sensor too, although disconnecting and jumpering it didn't make the CHECK BRAKE LININGS go away either.

    It's been dry for several nice days but the false warnings for brake fluid and brake linings are still there.

    So do I need to get an LKM and use my PASoft 1.4 to program it to match my car?
    '98 740iL E38 201k, TCG at 190k, 5HP24 at 195k
    '97 540i/6 E39 Dinan blower & stage 1 suspension 114k
    '93 525i E34 "Golf Ball" (hail damaged) 334k

  3. #3
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    The brake pad sensors are looped to the IKE on the same circuit. Any open circuit in the loop will cause the message. According to the manual, the red brake light comes on with the check pad warning, which I assume means it may just be an issue with the brake pad sensors circuit. The brake fluid sensor alone comes from the LKM. I can't remember if the brake light warning came on when I had a pad warning or not.

  4. #4
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    Quote Originally Posted by DrCharles View Post
    Nobody?

    I put new rear pads on today (they were getting thin, and the RR wear sensor was indeed touching the rotor). New sensor too, although disconnecting and jumpering it didn't make the CHECK BRAKE LININGS go away either.

    It's been dry for several nice days but the false warnings for brake fluid and brake linings are still there.

    So do I need to get an LKM and use my PASoft 1.4 to program it to match my car?
    I doubt such issue is caused by a not coded module, but PASoft (BMW Scanner) can only change the VIN number of the LKM module as far as I recall. You need NCS Expert or similar to properly program it but seriously doubt it would make any difference in this case.

    As for the check brake linings message, sorry I never run into it.

  5. #5
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    Quote Originally Posted by Mayorchuck View Post
    The brake pad sensors are looped to the IKE on the same circuit. Any open circuit in the loop will cause the message. According to the manual, the red brake light comes on with the check pad warning, which I assume means it may just be an issue with the brake pad sensors circuit. The brake fluid sensor alone comes from the LKM. I can't remember if the brake light warning came on when I had a pad warning or not.
    Thanks! As I mentioned in my initial post, disconnecting the fluid sensor causes a message to show up on the display and it goes away when the connector is jumpered or plugged back into the sensor. But the red light stays on.

    So, I am inclined to agree with you that the red light must also come on with the lining warning message. Just seems strange that the red light would be labeled "Brake Fluid" when the fluid is not, in fact, low. I was looking for the simplest explanation for both messages coming on within seconds of each other...

    Guess it's time to start tracking down an open in the pad sensor circuit! That's going to be fun. Electrically it is extremely simple but physically not so simple (sensors located at RR and LF wheels and wires/connectors running all over the car to get back to the IKE.

    Edit: I have tried the "key on for 45 sec" reset procedure, with and without driver's door open, key position 1 and position 2... no luck. As soon as I start the car, the red light stays on and the check linings message returns.
    Last edited by DrCharles; 03-03-2018 at 10:19 PM.
    '98 740iL E38 201k, TCG at 190k, 5HP24 at 195k
    '97 540i/6 E39 Dinan blower & stage 1 suspension 114k
    '93 525i E34 "Golf Ball" (hail damaged) 334k

  6. #6
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    Im sorry to not provide any help but I am curious, what is the key on 45 sec thing you mentioned?

    || 1995 740i || M60B40 || DUDMD || ̶o̶r̶i̶e̶n̶t̶ ̶b̶l̶u̶e̶ Mercedes Brilliant Blue Metallic || Style 168 Wheels 1" Spacers ||



  7. #7
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    See the bottom of this thread for Qsilver7's post. https://www.bimmerforums.com/forum/s...lining-warning
    Apparently the "BRAKE FLUID" light comes on not only with low fluid, but also when the brake lining sensor is triggered. It would make more sense to just have it say "BRAKE" but who knows what BMW was thinking.
    '98 740iL E38 201k, TCG at 190k, 5HP24 at 195k
    '97 540i/6 E39 Dinan blower & stage 1 suspension 114k
    '93 525i E34 "Golf Ball" (hail damaged) 334k

  8. #8
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    Quote Originally Posted by DrCharles View Post
    Apparently the "BRAKE FLUID" light comes on not only with low fluid, but also when the brake lining sensor is triggered. It would make more sense to just have it say "BRAKE" but who knows what BMW was thinking.
    If we were to take a poll...I believe the later model years (like 99-up) the word "FLUID" was removed from the "BRAKE" warning light. From memory, I don't think my 99 540iT had the word "FLUID" on the BRAKE warning light...and neither does my 06 e53.

    There could be a multitude of reasons why BMW has this BRAKE FLUID (or BRAKE) warning light come on when the BRAKE LINININGS warning comes on. It could be a "market" thing...since here in the USA...the BRAKE FLUID RENEWAL warning is programmed off. Perhaps that's the reason the BRAKE/BRAKE FLUID warning light illuminates.

    You can see the "clock" icon in the SI display below...in other markets...that clock illuminates as a warning to replace the brake fluid for its bienniel brake fluid change...but again, is coded OFF for the USA market (at least for the e38/e39/e46/e53 generation):


    You can also see the difference in the 97 e38 owners manual and 99 e39 owners manual in regards to the BRAKE FLUID vs BRAKE warning light. Again, I wonder what the 99-01 e38 high cluster says? Was it changed to just BRAKE? Facelift e38 owners....please chime in.

    {pre facelift e38 owners manual has BRAKE FLUID warning light}




    {my 99 e39 540iT owners manual warning light only says BRAKE}

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