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Just a Bad Coolant Level Sensor?

The Low Coolant Trouble Light in my 2000 Buick Century goes on and off intermittently. I have taken it out hoping to just find it all crudded up and then clean it but it was OK. The coolant level has always been perfect.Before I buy a new sensor, which at my local auto parts store is ~$50, and best Amazon price ~$14, might there be something else that could be causing the problem? Would knowing the resistance value and measuring with an ohmmeter tell me if my sensor is OK? Thanks in advance to replies to this post, I do appreciate any and all help here.

Check out this page and the tsb.

Check the wiring connections too. I had one that would come on and I finally just connected the wire to ground with an alligator clip to shut it off. It grounds through the coolant to shut off, so if you don’t have a good ground, either from a bad or gunked up sensor, or a poor wire connection, it’ll come on.

Excellent link, knfenimore, really gave me info that will help when I’m able to take the time to look into problem!
Bing, I was thinking about shorting to ground until I can spend more time on the issue. I’m guessing by what I read in the above justanswer link, that this would keep open a normally closed relay that powers the “low coolant” warning light, but wouldn’t want to cause that relay to have continuous duty for any length of time, so I’d need to deal with the issue before too long. Thanks for encouraging me to stop this warning light from it’s false alarm, which can be a bit annoying. Connections at the sensor look good and clean. But I know our old archenemy oxidation can be almost invisible.

Your car is 15 years old. The majority of cars on the road do not have coolant level sensors.

My advice would be to ignore or disable the light. Or cover ot with black tape.

Both my '99 Century and my '01 Regal had the same problem. I just ignored it. (Of course, I’d keep an eye on the coolant level. It was never low.)

I don’t know how a coolant level sensor works but it is probably more complicated than just a variable resistor. Likely contains some kind of transistor switch. It is probably just kaput and needs to be replaced. If the above ideas don’t get to the bottom of what’s causing this problem, that’s what I do, just replace the sensor with a new one. I wouldn’t want that light on all the time as it would distracting, and having that sensor working makes it less likely the engine will run low on coolant and you don’t notice, resulting in expensive repairs.

George San Jose, I’m thinking magnetic relay not variable resistor, or maybe an electronic relay.
Folks, indeed it is just in the “bell and whistle” category and not really necessary!

Maybe they have changed them but it was just a simple contact. The sensor itself just completed a ground contact through the coolant itself. No water, not contact and the circuit opened and the light went on. Water in the radiator and the circuit was closed and not light. Very simple. Just like those water sensors you can put in the basement to signal a leak, except reversed so that the signal goes off when there is no water rather than the other way around.

Sure, but the lack of current flow to ground would close a normally open relay to send 12 volt to pilot lamp, right? Or, was there enough current flow to illuminate some sort of low voltage lamp under the “low coolant” alarm on the instrument panel? Hey, I never thought of that! This could account for intermittent operation, not always quite enough current able to make it to ground to operate lamp? But then you’d think the lamp would have different degrees of brightness. So I’m back to my relay theory!
I’m so old school and used to 12 volt illumination and pilot lamps!

There’s a Buick customer interest bulletin on this issue apparently, where the coolant level sensor stays on when it should be off. That’s your problem, right? Good idea to ask at your Buick dealership, they can probably print it out for you.

If that’s the problem the cause is that there are contaminants in the coolant. Oil, something other than Buick’s recommended coolant, anti-leak additives, etc. That stuff can form a film and insulate the detector from the coolant and cause it to not work. The solution is to find out what’s causing the coolant contamination, fix that, then flush and fill the cooling system with fresh coolant to Buick’s specs. Either the coolant probe would have to be replaced, or you might be able to clean it. You can just ignore the light of course, but if you have contamination in the coolant best to discover what’s that all about, otherwise it may turn into something more expensive.

@Bing I agree with Bing. That sensor is probably the simplest of all sensors. It’s just a slug of metal that feeds through the radiator tank. When surrounded by the coolant the resistance changes from it to ground. I believe this signal is fed directly to the ECM with no relay involved. The ECM then switches the light on or off.

I had an '87 Cutlass Ciera With the same problem, exact same setup. In my case the terminal to the sensor was corroded. I cleaned it up and all was well.