Hello,
I'm new here and my first post. My Question. I have a Ford Tempo '91 GL, the error code read-out say << 54 >> = << IAT indicated -40C (-40F) circuit open >> ... What does that mean, and what is the problem? My Battery died on my more then just a few times, but it stoped 3 weeks ago to die on me, ...if this helps... Thanks

First - do you mean -40 Celsius or -40 Fahrenheit (they're never the same temperature). If your code reader said that - it's ***ked up.

Circuit open though - means something isn't switching off (and from what you said it's killing the bat. too).