What's Inside the Infamous Volt Battery Coolant Level Sensor?

The Gen 1 Chevrolet Volt is a great car that I cannot believe GM killed, but it has it's quirks.  One of the common problems is a Service High Energy Charging System (SHVCS) message that occurs which prevents charging the high voltage battery.  Many failures can cause this, but a common one is a failure of the battery coolant level sensor.  This results in a P1FFF DTC and sets the SHVCS.  If this code appears and the coolant is not low, then a failed sensor (GM part number 22922224) is often the culprit.  This device consists of 2 resistors and a reed switch sealed into a plastic housing and mounted to the bottom of the coolant reservoir.  When a magnet attached to a float in the reservoir gets close to the sensor, the reed switch closes and one of the resistors is bypassed, changing the sensed resistance and setting the code.  The thinking is that the reed switch becomes too sensitive over time and closes inappropriately (not because the coolant level is low)., causing a great deal of inconvience to the Volt owner.  Mine recently failed and I installed a new one, correcting the problem.  I decided to open up the old one and see what was inside. 

After trying to cut the goop that seals the components in, I applied some brief heat with a propane torch to the goop and that made it very brittle, allowing me to easily break it apart.  The first photo below shows the electronics inside, with the (now destroyed) reed switch along the bottom - you can see reminants of the glass tube that enclosed it.  There are 2 resistors soldered to the PC board that cannot be seen.  I removed the reed switch and measured the resistance to be 24.6 Kohms, which is the correct resistance if the tank is full.   I sealed it back up with hot glue.  Now, this is essentially a by-pass that fools the computer into thinking the coolant level is fine.  I intend to use this temporarily if the new sensor fails, until I can get a new replacement sensor.  I don't recommend this as a permanent fix since if the coolant level really is low, you want to know it.  This is such a pervasive problem with these cars that one can purchase a so-called "defeat plug" for about $40.  This is a poor-mans version of what is commercially available and cost only my time.  Hopefully this will help others that have encountered this problem.