W124 engine coolant guage

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tintinmt

Active Member
Joined
Feb 1, 2009
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364
Hi, I have no reading on my engine (M104 300TE 24v) temperature gauge. If I short the cables to the coolant temperature sensor the fan cuts in. Does this indicate a failure of the gauge or the sensor? Any tips on diagnosis?
Thanks.
 
You need to short the green wire to earth, that should test the gauge.
 
I tried earthing the cables and got the same result as shorting them out - fan kicks in but no movement in the gauge. Also checked the resistance of the sensor - it seems to change with temperature. Then checked the voltage to the sensor - seems to be around 5v. This all seems to point to the gauge itself being faulty to me. Any thoughts?
Thanks, M.
 
It sounds to me like you're shorting & grounding the wires to the aux fans temp sensor (they're switched according to coolant temp and/or aircon refrigerant pressure)? I'm not that familiar with the 300-24 but typically there are three sensors in the thermostat housing, one larger plug for the engine management that goes in 'sideways' lower down and two smaller sensors fitted in the top. Of these the two pin plug is for the aux fans and the single pin for the temp gauge
 
There's only two pins on this one that I can see. Thanks.
 
That sensor is for the air con, there should be another with a single pin.
 
Thanks, it really helps if know which is which :).
The wire had snapped in the connector - all sorted now.
 

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