Code P0118

I have seen a slight decrease in my mpg as of late accompanied by a cel. Went to autozone today and came up with p0118 engine coolant temp circuit high imput. also a bad o2 which may be my o2 heater and is prob my mpg problem.

Anyway, im looking for the casue of the coolant temp. I checked temp sensor at the t-stat housing cold then hot....cold read 12.5ohms hot read 1.2 so it seems to be opening when hot....theres 5v at the connector when powered...i assume those reading are normal. The t-stat is a new chrysler part as of last year....strange story behind that...

Jeep was running great but coolant was brown so i decided to flush it and change the t-stat....after it was all done and purged, the temp ran at one tick colder on the temp gauge. I swapped the cheapo stant for a chrysler unit and it still ran a tick colder.....only thing i could think of it the fan shround that i broke during the t-stat removal....dont see how that would effect the temp tho....

98 4.0 ax15

Are there any other temp sensors on a 98 that would throw that code???
Also i have to hit my gauge cluster from time to time since it jsut goes dead at times

I think the 98 uses just one coolant temp sensor for the PCM input AND the gauge/idiot light.

As only the sensor feeding the PCM would trigger a code, I would say no there isn't any other coolant sensor, just the one in the thermostat housing.

Pull the instrument panel and clean the contacts of the connector, coat with dielectric grease, see if you can "tug" a little extra slack in the harness, then reconnect everything--this is a common problem of the 97+.

Ever solve the P0118 and P0171 issues? Had both of those pop up last weekend. I suspect that either my CTS and upstream O2 sensors got banged up recently (both look fine but had opportunities to be abused recently) or the really crappy ground strap from the rear of the cylinder head to the firewall is making for a bad ground reference. I plan to replace the ground strap with #2 wire and see if it reoccurs but you have exactly the same codes, so I figured I'd ask.

Wondering if some of these CTS errors could be related to scale/deposits on the sensor itself.

Just for grins, why don't you pull it and clean it up with some steel wool, see if that changes things.