2004 TB SES light came on. Had Autozone scan codes.... came back as "PO128 Coolant temp too low". Reading on temp gauge was 190 degrees, while it normally runs around 210. Engine running great though. Figured thermostat must be stuck open. Picked up a new thermostat and coolant temp sensor. Decided to change the temp sensor when i changed the thermostat, due to the terrible access.
However, when i removed the thermostat, it was closed. Changed it anyway along with the temp sensor. Worst part was getting the lower rear bolt on the thermostat housing back in. Had to remove the front wheel just to see where the hole in the thermostat housing lined up with the hole in the block. My hat is off to all of you (liars) who were able to change it without pulling the alternator!!
Put it all back together..no light, no leaks..just some minor bleeding. So now its fixed, I'm just not sure what caused it in the first place? Would a bad coolant temp sensor cause PCM commands that result in a lower engine operating temperature??