Trying to sort out the sensors that are located on top of the head near the valve cover. What are each of these and their respective function?

One sends signal for the dash temp gauge, another monitors coolant temp, but what each of them does I am not certain. Any clarification offered will be appreciated

Dale

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Dale

Front by the oil port is some thermo vacuum switch. It opens or closes after a certain temp. You would have to trace the lines to see where they run, maybe the evaporative emissions stuff.

Single pole is the sensor for gauge cluster.

The two pole by the breather I think is the aux fan trigger.

Rear should be for the ECU.



Been a while since I have been up close with an early M103 layout

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

The one closest to the firewall is a dual thermistor with the case as the common ground. One temperature sensor is for the ECU and the other goes to the ignition module.

Later models used a 4 pin sensor that had 2 ground wires so it did not depend on the case making a good ground with the head.

Thanks for your input!


Any chance that one of these has a direct affect on when the climate control *should* begin functioning after it has sat overnight? I'm trying to figure out *why* the climate control sometimes starts 'blowing' as soon as I start it up to pull out of the garage and other times not....thinking it could be a coolant temp sensor on the block. Could be wrong - probably am


Dale

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Dale

The one with the blue tape on the wire is for the climate control.

Resistance values as of 09/87:

5.0 - 8.0 k ohm @ 20 degree C
900 - 1800 ohm @ 60 degree C
460 - 650 ohm @ 85 degree C
300 - 400 ohm @ 100 degree C

You should be able to pull codes from pin 7 of the diagnostic connector near the battery.

Thanks Rick for this info. I'll need to dig out my tester I made several years ago and relearn how to set it up!

A *dumb* question: will I need to remove the sensor from the head to test or can it be tested in place? I'm guessing in place...

Dale

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Dale

Just unplug it and check with an ohmmeter between the 2 pins.
Also check to ground, which should be infinite resistance.