OBDII P0125 trouble, celi is not passing emissions Options

[f1yen]

I had 4 codes, but got it down to 1.
P0125, insufficient coolant temp for closed loop fuel trim

So far I have new thermostat, new ECT.
When checking the o2 sensor (upstream), if it is unplugged and I check the voltage between the leads, My values are within range 0-1volt. so thats good.
When I hook the connector back together, and backprobe to get a voltage between the leads, i get a constant .5 milivolt....

I checked the wiring between the conectors and the diagnostics box, and from the connector to the ecu, to see if I had a low resistance > yes
Then I thought that maybe a wire is corroded or something that it cant handle the ammount of power through it... so I wired a direct line from the sensor output to just before the ecu. but same.

(for reference I also had a code for P0141 which is a faulty downstream o2 heater circuit, but i just hot wired some resistors to put the ecu at rest; at least for emissions)

Any help would be appreciated.

[f1yen]

Well just to sum this post up, <sorry this is way late>
I did replace the thermostat, and tried a spare temp sensor as well.
Both o2 sensors appeared to be working fine... as well as the wiring.

The problem was some short in the wiring harness, when the car was warm and running a short would develop between the signal wire on the primary o2 sensor and ground..(assuming on the shielding) . so when checking the o2 sensor wiring (check for proper ground, proper wiring of the signal wire to the ecu, also check connectivity of the signal wire to ground[should be none]) Mine was intermittently shorting on ground, and luckily I was able to find it one of the times i was testing!

I proofed this fix by running jumper wires directly from the sensor to the ecu (but if it is like my case, make sure you clip the original sensor wire after your splice by the ecu, so that it will not keep grounding the signal)

After this setup was working for a week, it was fully installed. Thanks for the help.

I have some ECU's hangin around the garage if anyone needs em!

-Kyle