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Temperature Sensor Random Issues

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So I think I’ve tracked down my random cold start up idling issue. Just installed the REM into my truck. It had been idling for some time and I set it up to view the water temp. It was reading 246 which wasn’t correct but the truck was running great. Today I go to crank it up and it starts running horrible. I notice in the screen that water temp read -46 degrees. That’s pretty much impossible since it was 50 degrees outside.  I am assuming an incorrect reading to the ECU will definitely cause my idle issue but any insight is greatly appreciated. 

On a side note I let the truck rest for a bit and tried it again. The temp was correct this time and fired right up. 

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1 hour ago, cruiser54 said:

Unplug and clean the connector on the CTS. 


Also make sure the harness to the CTS and O2 sensor are routed correctly and not shorting out. 



Harness connectors and routing.jpg

Harness routing.JPG

Yep. Been through all this last year. Went through the entire engine bay checking everything you listed on the website and some more suggestions from discussing it with you on this forum. Everything appears to be good. This is the only thing I notice that’s off on the REM. Everything else appears to function correctly. Does that sensor influence fuel mapping in anyway?  I was under the impression it did from some reading but it’s still not clear to me. 

ill. Heck to make sure something isn’t grounding out that circuit again. It’s odd that it read 246 and -40. Seems like a ground out would cause one reading or the other but not both. 

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Feeling a little better from being sick this past week and took the truck out for a little cruise to get out of the house. Looks like the sensor on start up read fine. Climbed as expected but it keeps going until it pegs at 246. The gauge reads fine. The fan doesn’t come on etc. I’ve verified temps with very precise instruments I used for BLDC motor tuning for temperatures (one perk of my job). I guess what doesn’t add up is the -40 reading I saw. 

So I guess the next steps I am taking will be pulling the CTS and replacing it with one I have confirmed correct. At that time I will go back through the wiring and check it again but nothing has shown itself but it doesn’t mean I missed something. 

Here are a few readings from the cruise around town for reference. 





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