Added Coolant Light - Easy DIY

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New member
Nov 1, 2022
I've owned my 2014 FFE for just under 7 years and am out of the HV battery warrantee period by over a year. With a 15 year old getting ready to drive, I'm hoping to extend the life of the FFE well past it's current 70k miles and pass it on to at least one of my two kids as a high school commuter. HOWEVER, I've been lurking on this forum long enough to worry about coolant leaks in the battery modules and basically "totaling" the car.

I'm not a good auto mechanic but pretty handy with electronics so I got to thinking: "Why not add an aftermarket sensor to the coolant tank and a warning light on/near the dash?" I recently ordered and installed a non-contact fluid level sensor, affixed it to the coolant tank and wired it to an LED between the dash and "START" button. This took me several hours but now I can sleep easier not needing to regularly check my coolant level and worrying about the battery becoming "bricked" by something I could monitor.

I don't know that my setup is robust enough to last more than a couple years but I am pretty confident the scenario of a false positive due to my DYI failure will annoy me a lot less than missing a coolant leak and a damaged battery / useless car.

For those that want to replicate what I did, I ordered and installed <-- this mini sensor (running through a LM7805 5VDC voltage regulator I had in my parts bin), and wired it from a switched fuse.

After I ordered the liquid sensor but before I did the interior LED wiring, I found this nice write up... nearly the same as what I did.

Hope to never see the LED come on, but if it does, I'll be pulling over quick and be relieved it is just my sensor coming off the plastic tank or similar. To the few of us still enjoying our out of warrantee FFEs, hope this inspires you to consider this easy DIY addition. :)
What are the chances we can put a similar sensor at the bottom of the battery case and look for the light going off as a warning? Would be far more sensitive and only trigger for coolant leaks in the battery itself...