Ok, Im gonna keep you guys busy, lol looks like there hasnt been too many threads, so here it goes, I keep getting a CEL, it will come on when driving for no more than a minute, less sometimes, then shut off again, I checked it with our dealerships super old Tech 1 and it said Oxygen Sensor Circuit, so I said ok, the 02'* bad, so I replaced it, and its still doing the same thing, what could be causing this to keep on happening even after replacing the 02? For info, I use all OEM AC Delco parts in my car.

It sounds like like the problem is occouring once the PCM goes to close loop mode. This is when the O2 is looked at by the PCM, before closed loop it is in open where it is ignoring it. A scantool would be helpful to verify the the o2 is providing data correctly. It should pulsate constantly


I'm not going to speculate what else could be the issue other than possibly a wiring problem. Perhaps someone else will chime in with some other ideas if you dont have access to the scantool.

Shoot the wires with an ohmeter. Sounds like connector corrosion but, a scantool will tell you if it'* hitting high or low.

First thing to check is ensure the O2 wire is not touching any of the plug wires.

Using the scan tool, watch the O2 toggling (rich/lean). If all seems well there, move on to other sensors etc.

And above all else, check all ends of all battery cables, including under the rubber boots. Corrosion is a bonneville'* #1 enemy. Every single one can suffer from bad connections/corrosion.

I tried to see if I could read what the 02 is puttting out, but the Tech 1 wont tell me that, I think, Ill have to try it again, also, could my coolant temp sensor cause this? As soon as it hits operating temp, the needle drops to the line between 100 and the halfway point, sometimes even colder if its really cold out, and will keep on fluctuating from operating temp to that line. I think this is just becuase of the location of the sensor, and shouldnt be causing my 02 problem?

Damemorder, which wires should I test? The plug wires or the one 02 wire?

Anytime you replace a sensor you should remove the neg battery cable for 30 min to re-set the ECU. This is a good time to clean the cables also. Just make sure you attach the neg. last.
Your temp gage shouldn't fluctuate that much. sounds like a weak thermostat spring. Best to replace it with a new one.

I just did replace it, the motor wasnt warming up, only just above 100 degrees, the thermostat was stuck open, so I replaced it with a new one, but now the temp just jumps up and down, not rapidly, but steadily, you can tell through the gauge when the thermostat opens, as the temp will drop to that 2nd line fairly quick, but I think this is just due to the location of the coolant temp sensor, am I right?

Nope. Sounds like you've got an air pocket.

what happens is the coolant will reach operating temp or just shy of it (according to the gauge) and then will drop, and it will keep doing this, its not like its rising above operating temp then dropping back to operating temp, whats a good method to purge out this air pocket, this damn car has the shitty thermostat housing with one bolt and no bleeder.

This is how I did it after I changed my heater core. It may not be the easiest or cheapest, but it worked for me. I ended up wasting a little bit of antifreeze, but I think the peace of mind of knowing the cooling system is properly burped is worth it.
I live on a hill so I got the car almost level, but had the nose pointing slightly uphill with the right side of the car slightly higher than the left. This places the overflow tank at the highest point in the cooling system.
Fill the radiator. Replace the radiator cap.
Fill the overflow tank all the way to the top, but don't put the cap on it.
Start the engine and let it idle. Turn on the heater as hot as it will go.
Baby sit it, making sure that the level in the overflow tank stays higher than the thermostat housing. This should be no problem if you have the car inclined correctly. Use the jack if you have to.
The cooling system will eventually self burp out the bubble or air pocket. It may suck down the level of the overflow tank, but that is why you are standing over it baby sitting it to keep it full. It may also puke out some antifreeze. BFD that'* what car washes are for.
I let mine idle for about a half hour. That is probably much longer than necessary. At some point, the level in the overflow tank will stabilize. There may be a periodic surging or draining as the normal ebb and flow of the thermostat cycling runs its course. If you have constant bubbling that doesn't subside after a half hour of keeping the overflow tank full, you most likely have a bad head gasket. Any other problem like a bad intake gasket should show a leak.