So I've been struggling with the CEL that thinks the coolant level is low for months on and off, I forget the actual code. I read about it here and the bypass resistor that folks used to fix it.
I made my own and tried it and it seemed to work, however on a recent long trip it came back, I reset and then a couple of days my car went into limp mode.
I did some more digging and decided to put a new pigtail harness in for that sensor. Amazon had the part PN 13586114
Today I changed it out, to my surprise the old pigtail was wired in to a very high standard, soldered very neatly and heatshrink used. I was starting to think it might have been something else.
When I finished the job I examined the old one, and found the fault. Using a multimeter and wiggling it I could make an open circuit on the black wire. It looks like the old wiring is much smaller gauge and more at risk of vibration fatigue, the new one is much more beefy. In addition I used a long service loop of wire and added much more strain relief, protection and heat resistant kapton tape.
I put a new reed switch sensor back in, so now my coolant sensing is working as stock.
When I removed the connectors from the plastic the white wire came out fine, the black one failed. So it looks like it broken inside.
Thought this might be helpful for others in the future. I have one more annoying bug to fix, which is a CEL caused by out of range engine air intake sensor. Does anyone know the fix for that? perhaps more bad wiring??
FYI my car is 2011 with 120600 miles on the clock