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Low Cooloant Level - PCM

 
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2001Ls
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2001 Chevrolet Impala


PostPosted: Wed Aug 12, 2015 5:01 pm    Post subject:  Low Cooloant Level - PCM Reply with quote

2001 3.8

My low coolant light is intermittent, I cleaned the probe on the sensor and my coolant is to the neck of the radiator. When I disconnect the sensor the "low coolant" message is off. So, heres where my post gets fun and youre a smart person if you can answer.

I'm trying to understand the electrical design behind the coolant level sensor. What is has is (1) 12v power feed and (1) ground wire connected to the senor. If you unplug the sensor the light goes away. I cant find a full wiring diagram, so I don't know how the PCM or BCM monitors voltage or current through the coolant level sensor. But, and I don't see how this could be wrong, if there is no continuity and no current through the sensor the PCM or BCM identifies this as a full coolant condition. I assume this because with the connector unplugged the light is off. I was doing some research and the type of coolant level sensor on my car seems to function by reading the resistance in the radiator (coolant will have a resistance that will fall within spec, thus causing a voltage drop within limit).....this however seems counter-intuitive to the fact that by creating an open circuit by unplugging the sensor puts the light out...


.....anyways to sum up I'd like to understand how it works, don't want to shoot parts at it. Another possibility for the intermittent light is that my coolant is too diluted (too high water content)...this is a possibility because I know I have a higher than specified water content and if the system is in fact reading resistance somehow it would make sense... Just looking for thoughts and any knowledge on these senors. Thanks for any help.

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2001 Impala LS 81k as of Nov,2011
3.8 V6 3800 Series 2
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Frank
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2001 Chevrolet Impala


PostPosted: Thu Aug 13, 2015 3:49 am    Post subject:   Reply with quote

Besides gunking up, the sensor can also tarnish/corrode which will cause false low coolant lights. I've never thought about it much but the car knows when it's plugged in or not plugged in in some manner so I've never really worried about that part of it.

You could also have a bad sensor.

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2001 Galaxy Silver 9C1 w/ L67 and 4T65E-HD...and a few other mods. Wink
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2001Ls
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PostPosted: Tue Aug 18, 2015 9:16 pm    Post subject:   Reply with quote

I think I found a picture of a similar circuit......theirs 2 parallel paths to ground, one with a fixed resistor and the coolant probe and one with a NPN transistor. The coolant is acting as a conductor dropping voltage when submerged. The side with the coolant probe , when open, powers the P side of a NPN transistor competing the "low coolant" circuit to the PCM or BCM....couldn't find the picture because I had it on my phone.....anyways I think in my case the vacuum return valve in the radiator cap was sticking....it would get hot and expand dump into the overflow but when it cooled down it wouldnt suck any coolant back into the radiator. Cleaned it up and its not acting up

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