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CLK320, 2000 and E270 CDI, 2004
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Discussion Starter · #1 ·
Disconnecting my faulty oil level sensor means that I still get the malfunction message. Does anybody know how to cheat the system i.e. what signal is expected for correct oil level. There are three connecting pins with 5V output on the centre. (Checking oil level by dipstick is good enough for me)
 

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CLK320, 2000 and E270 CDI, 2004
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Discussion Starter · #4 ·
Adding oil without need or replacing the defective sensor will just cost money without giving any added value for those who regulary change oil and check by the dipstick.
Please an answer by someone with knowledge about the wiring diagram.
 

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'00 CLK430 Cabrio
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52 Posts
If it were me, I would replace the faulty sensor as I'm sure I would invest more time and energy trying to figure out how to trick the system versus replacing the faulty part.

To me, the oil level sensor represents the "hands off" approach typical of a segment of MB owners, but is not quite as ridiculous as the tranny dipstick that resides at the dealership (unless you have your own).

I think the vast majority of folks at this site are "hand On", and like you rely strictly on the dipstick.

I've attached the how-to on replacing the sensor, in case it's useful.

Good luck.
 

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CLK320, 2000 and E270 CDI, 2004
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Discussion Starter · #6 ·
Thank you Dan for your friendly reply!
I have however already dismounted the sensor once and tried to clean it and make it work again. As beeing a hobby mechanic I'm not at all afraid of the work (in fact I like it! :)
If the solution is just to connect the 5V to any of the other two pins then I think this would be the preferd solution by more than me. Less work and avoiding the cost of extra oil change, level sensor and pan sealant.
Besides that I'm also interested in how it works, capabel of giving three different messages low, high and faulty.
 

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Premium Member
2004 CLK 240 Coupe
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11,385 Posts
Disconnecting my faulty oil level sensor means that I still get the malfunction message. Does anybody know how to cheat the system i.e. what signal is expected for correct oil level. There are three connecting pins with 5V output on the centre. (Checking oil level by dipstick is good enough for me)
You cannot cheat the level sensor (B40) in your M112 engine.

The sensor in the oil sump is a complex piece of electronics that sends continuous data on a) oil level, b) oil temperature, c) oil quality, to the ME- SFI control unit (ECU).

The data on the 3 functions is processed and sent as a pulse-width modulated, square-wave signal to the ECU and then transmitted via CAN bus to the Instrument cluster.

Full details on drawing below. If you can defeat this - you're a better man than I am, Gunga-Din! :)
 

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CLK320, 2000 and E270 CDI, 2004
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Discussion Starter · #8 ·
Ok, admit that I've come to the end of the road and will replace the sensor.
However very pleased because learning is life.
Thank you very much for the informative pdf! I will cut open the defective sensor and see what it looks like inside.
 

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CLK320, 2000 and E270 CDI, 2004
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Discussion Starter · #9 ·
For those who are interested, this is what the sensor looked like inside

Green wire at bottom for temp measure. Three wires for the capacitive level measure.
The circuit board in the outer part was all soaked with oil because leakage through the bottom of the inner sensor into the wire harness (taken away on the picture) and over to the circuit board.
Thus it might be a good idea to open the rubber hose harness and put a silicon sealant to the bottom of the outer part when changing to a new sensor.
And if you dismount the sensor just to change the O-ring be careful not to tilt or turn the sensor upside down as you might pour oil from inside the harness over and into the circuit board.
 
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