Yesterday, I was driving my 1992 300e and my 4 Matic warning light came on. I followed a test procedure that I found online and this was the trouble code that I found. "10-Hydraulic valve 3, short- or open-circuit, OR brake switch defect." Can anyone tell me what I should start looking at? I'm new to this. Thanks

Start with the stop lamp switch. These are very common on the 4-matic.
They are also fairly cheap and easy to replace.

If that switch is bad, does that mean that the brake lights will not illuminate?

Are your brake-lights European nickle-plated sockets with 21watt bulb or US-style copper-base?

Mine threw brake-light switch codes with a US-style replacement brake light bulb.

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Gone to the dark side

- Jeff

No the brake lamp switch can cause the code with the lights still working.

I have idea. How can I tell?

How do I tell if it is the problem? Just replace it?

Yes. They are cheap and easy to repl.

I ordred the part. Is it ok to drive until I Change it?

yes

I just replaced the switch and it worked. What a relief! What does the brake light switch have to do with the 4 Matic? Thanks for the advice!

the brake switch has 2 other functions.when the peddle is pushed it activates the ABS.when released it activates the 4 matic.

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michael cole 1980 300SD gone now but not forgotten,87tdt,90 300te 4matic 95 e320 wagon