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Discussion Starter #1
Greetings. I own an E46 coupe FL from 2003. An issue I've been dealing with for a couple years now, is that very rarely I get an error code. This translates into the yellow E-brake light, and the yellow DSC-off light. DSC and ABS are gone. If I turn off the ignition and switch it back on again, there's a chance that it's still there, or comes back within 10 minutes. There are 2 sensors on your master cilinder to measure your brake pressure. 2 sensors, as a failsafe / check. One of these sensors throws a code every now and then. I tested the pressure of both sensors together with a Delphi system, and both go up & down evenly.


Now, the thing that I can't seem to understand is: 9 out of 10 times, this happens in the summer on a very hot day. I cannot remember having this problem during winter or anywhere away from the summer actually.

Does anyone here have an explenation for this?

Kind regards
 

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Yup.

There are electronics in the sensor. When it gets really hot, the sensor itself malfunctions. On really
'hardened' electronics (think military) they have a mode that prevents them from burning themselves up,
so that when they cool off again, they stand a chance of 'coming back to life'

So I'd guess that you have a sensor that's either starting to fail, and heat is pushing it over the edge,
or one that's overly sensitive to heat.

Easy to test the sensors themselves, either with 'freeze spray' or a cup of cold water.

The ABS elecronics can fail in the same way, losing one A-D sensor out of many.
Yes, those sensors are analog.

hth
t
 

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2004 330Ci 85k miles
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What is the actual trouble code and its freeze frame data from INPA? Maybe post a screen shot?

It could also be an intermittently failing ABS control module. Switch the sensor connectors and see if the error code follows that or stays at the same position.
 

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I had issue that seems nearly identical with same seemingly random DSC errors. Finally realized error was occurring from heat build in the engine compartment. Spirited short drives on hot days (I'm in TX) or long runs on the highway both could trigger. If shutdown, and engine cooled, error would clear. If restarted with engine was still hot, might re-trigger immediately. I could reliably trigger an error with 1 1/2 hours of highway driving. Believe root cause was likely a failed solder (i.e. cold solder) joint in the DSC that would open when sufficiently warmed. Set up BMW Scanner and took a highway error to trigger/trap the DSC error -- it was a "control unit internal failure". Replaced DSC with unit from 2004; issue resolved with no reoccurrence. Apparently this is not uncommon on DSC units prior to a revision in 2004. Will try to find my thread and post a link.

Here's link to my thread. BTW, for the price, suggest follows Orb's advice and replacing the brake master cylinder when making this repair. Biggest challenge I had was getting the brake system to fully bled. GL
 

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Discussion Starter #5
Thank you all for your input.
@BaliDawg : I used to have a screenshot but I lost it somewhere on my computer :p But it was something like: "BRAKE PRESSURE SENSOR: intermittent error or short circuit to ground" something like that.

It was this exact same code that always came back.The only question is: which sensor is it on my master cilinder, if there are 2 identical ones?
 

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Thank you all for your input.
@BaliDawg : I used to have a screenshot but I lost it somewhere on my computer :p But it was something like: "BRAKE PRESSURE SENSOR: intermittent error or short circuit to ground" something like that.

It was this exact same code that always came back.The only question is: which sensor is it on my master cilinder, if there are 2 identical ones?
The trouble code text will mention which sensor, 1 or 2, A or B, something like that. Google around for examples.
 
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