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Old 03-13-2002, 08:40 PM
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Cool Coolant sensor circuit terminology

The coolant level sensor light on my instrument panel recently went on and stayed on, even with adequate fluid levels. I used the search button on this site to review others comments to help me diagnose and fix this problem. All agreed that the level sensor could go bad and need either cleaning or replacing. However, there was some confusion as to what the terms ‘opened’ and ‘closed’ mean and how being ‘open’ or ‘closed’ affects the dash light being on or off. Some associate open circuits with the dash lights on and others with dash lights off; examples from 4 different contributors:

#1… unplug the wires at the sensor. If the light goes out, it is a bad sensor…I t should close (zero Ohm) when coolant level is low and open (infinite Ohm) when coolant level is high.
#2…a leaking sensor (common) can short internally, thereby closing the circuit and activating the dash warning light.
#3… open or short will cause COOLANT lamp to come on.
#4… pull the plug off the sensor and see if the light is on (probably will be - open circuit) then I would take a short wire jumper and short the two leads together at the plug which should simulate proper antifreeze level.

I appreciate having this helpful forum available, so in an effort to help clarify terminology, I will describe what I found in fixing my errant coolant lamp. Firstly, unplugging the sensor led to the dash lamp going off. The sensor is built sort of like an alligator’s jaw, dropping down (physically opening) with low reservoir coolant levels and rising (physically closing) with adequate coolant levels. I removed the old sensor and used an ohmmeter to find it had no resistance in either the physically open or closed position; I consider this a closed (or shorted) circuit. The new sensor had great resistance when the jaws were closed (I consider this an open circuit, simulating adequate coolant), but no resistance when the jaws were open – simulating low coolant.

In summary, I associate open circuits with high resistance (ohms), this occurs with either proper fluid levels or unplugging the sensor. I associate closed circuits with zero resistance (ohms), this occurs with either low fluid levels or a short circuit. I am certainly not an electrician – what is considered the standard terminology here?
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