Service engine soon light came on a couple days ago, 1996 CE LT4, 13.5k miles on the clock. Had auto store run the codes, only had one show up, P0125, insufficient coolant temp for closed loop fuel control. I cleared the code and the service engine soon light came back on again today. Car runs fine, coolant temp routinely runs about 190-195. I changed the coolant and installed a new thermostat when I got the car back in late May. Did some reading and checked the gas cap and coolant level is where it should be. Could it be the O2 sensors? What other things could it be?

Thanks in advance for any feedback.

 

Coolant temp barely gets above 150 degrees.....possible the thermostat is stuck open??

Any thoughts?

 

Seems like the usual suspect to me

 

Crazy if that's the case (the stat being stuck open). I replaced all the fluids when I got the car in late May, new coolant and at that time put in a new thermostat.....that stinks if I gotta do it again only 5 months later. I guess that's worth it for the first shot at fixing it.

 

I don't know, may not be your issue. But it seems like a reasonable look. Not that difficult to get the stat out with only draining coolant a gallon or so. Last AC Delco thermostat I bought was defective right out of the box.

 

I picked up an AC Delco stat, and both temp sensors, last night on my way home from the office. Swapped out the stat and saw why the one I removed was not working properly, one part with the way the spring sits had come off its place/wasn't seated, so I suspect that was the failure of that. Popped the new AC Delco one in with no problem. Then I did the ECT sensor on the front, relatively easy to do. I decided to wait on the sensor that goes on the passenger side of the engine. I have the part and decided I'll swap that one out when I do the spark plugs....which is on the list to do soon.

Drove it a bit last night after doing the above. The temp started going back to normal op temp immediately, as expected with the with the new stat. Drove it around the neighborhood, then down the street and on the highway a bit.....check engine light still was on. This morning, got in her to drive to the office and the check engine light came on initially, but then after a few minutes (prolly 15 mins or so), the light when off. So, that apparently solved the problem!

On to the next item on the to do list....guess I'll tackle the spark plugs sooner rather than later.

 

Glad that problem was relatively easily solved