How do you know it's bad?
My red lite wouldn't come on when I tested it at home before this trip we are on now. At home it was 55 degrees outside.
I got to sunny, spend the winter in comfort, Arizona where the temp was 22 degrees.
I turned on the water bay heater light came on and it actually warmed up the bay enough to thaw my water lines.
So I think the outside temp has to be low enough to allow it to come on.
2004 Monaco La Palma 36DBD, W22, 8.1, 7.1 MPG
2000 LEXUS RX300 FWD 22MPG 4020 LBS