2005 Chevy Silverado Temperature gauge does not work

Hi, I finally got my hands on a code reader - here are my findings:
Two codes came up
Primary code = P0118, engine coolant temperature circuit high input. Freeze frame date for this code =
Fuel system 1 = open load
Fuel slystem 2 = open load
Calculated load = 0.0%
Engine coolant temperature = -39 F.
STFT Bank 1 = 0.0%
LTFT Bank 1 = 5.4%
STFT Bank 2 = 0.0%
LTFT Bank 2 = 3.1%
Intake manifold pressure = 28.0 in. Hg.
Engine r.P.M. = 000 r.P.M.
Vehicle speed = 0 mph
Ignition timing = 0.0 degrees
Intake air temperature = 66 F.
Mass air flow sensro = 0.00 lb/min
Throttle position = 18.4%

Secondary code = P0116 - Temperature circuit range/performance. This code comes up as a "pending code".

Another point that might be worth noting:
When I initially plugged in the code reader the first code came up as a "Red LED" code
After I disconnected the reader and reconnected the code came up as a "yellow LED" code - not sure if this is normal as I have never used a code reader before!

Another interesting finding - after I noticed my electrical problem I was scrolling through my instrument cluster data information which includes odometer, oil life, trip meters etc. My total engine hour meter has defaulted back to zero hours - looks like the computer has lost some memory? All other data is as per what it should be. Hope this information helps determine what my problem is. Thanks and look forward to your reply. Claude

Hi Bob and Ken
I think it may be premature to start replacing sensors at this point as there is some information that has not been communicated properly to you. It would be considerable easier to call you by phone - is this possible? If so, send me your number and I will call you. If not, here is some of the information I gave you that has not been answered which I believe could be key to the problem.

The temperature gauge works fine when the service light goes on when the ignition switch is turned on - but only works for a short period of time. Please comment/explain this.

The temperature gauge does not work at all when the service light does not turn on when the ignition switch is turn on. Please comment/explain this.

Why is the service light not going on everytime the ignition switch is turned on - the owners manual says it should - please comment/explain this.

This leads me to believe the temperature gauge is not the root problem but the fact that the service light is not activated when the ignition switch is turned on is the root problem. Please comment.

My understanding for the "Freeze frame Data" is what/where the engine condition was when the code originated - if this is true, the engine coolant temperature of -39 F. Means simply the temperature of the coolant when the code occurred - yes it is cold in this country! This is further confirmed by the rest of the freeze frame information - ie engine rpm at zero and vehicle speed at zero. Please comment.

Can you explain why the engine hour meter has defaulted back to zero hours? Please comment.

One other piece of information that may be helpful. After I noticed my temperature gauge not working it was noticed that a mouse or mice had got inbetween the engine and firewall ( directly in the middle of firewall or directly behind the intake manifold) and chewed up some of the insulation. I spent a couple hours cleaning up their mess and looked very close for a chewed wire - nothing was noticed but I certainly could have missed something hiding in that area. Is there electrical wires in that area that would be connected to the "engine service light/hour meter clock/temperture gauge that could be the reason for all of the above? Please comment. Thanks in advance for your time and patience on this matter. Look forward to your reply or phone number. Cheers Claude