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.

lets hit up al's this weekend and try to get a different ecu, they have a few st's laying around

>

mmk I know Im goin on Sat. Im also planning on doing one final trial tonight, possibly tring to see if routing the o2 grnd another way @ the ecu will help??

Ok so update, gotta ecu (but A/T) and hooked it up, same code P0125, along with some others for the shift interlock solenoid (A/T)

so I'm assuming that I can not have 2 bad Ecu's?

do you think that it could be from the fact that the engine is a 4afe and the ecu 7afe? (but i got it to pass emissions 2 yrs ago like this)

have you checked that..
1. the thermostat is maintaining the proper engine temp?
2. the engine temp sensor is working correctly?

new doesn't mean its working right. also, the O2 sensor heater DOES help the sensor to read correctly, narrow band sensors need to be 400-600F to read right. try replacing the sensor.

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