How To Clear O2 Sensor Code

after I connected the battery again, it shows a pending P0300 code (random misfire). Only other time I've ever seen this code is one time after I had pulled the fuel pump relay to check pressure, and it cleared within 2-3 drive cycles. hope it's something similar this time.

Mooseman

Quite possibly, with the bad O2 sensor, it couldn't detect the misfire. Now with a functioning sensor, it sees a misfire or the sensor you got is a dud. What brand sensor did you use?

And after resetting the PCM, you might need to clean the throttle body if it's been a while, although that would result in a bad idle or stalling when using the A/C.

Mooseman said:

Quite possibly, with the bad O2 sensor, it couldn't detect the misfire. Now with a functioning sensor, it sees a misfire or the sensor you got is a dud. What brand sensor did you use?

And after resetting the PCM, you might need to clean the throttle body if it's been a while, although that would result in a bad idle or stalling when using the A/C.

I cleaned the throttlebody a few months ago. went back in there tonight as part of my hunt for the 0171 cause, and found the bolts holding the throttle body on were loose (but it was still shiny!)... I wonder if there was a leak from it being loose. my fuel trims look a little better but it's too soon to tell.

BlazingTrails said:

Just don't clear the p0300 code. If you keep driving it you may get a code for a specific cylinder or 2. Probably need new coils.....

that would be awesome, because heaven knows I don't put nearly enough money into this crapcan. Looks like those are about $42 a piece...do I have to do all six at once, or can I get by just doing the ones that are misfiring?

BlazingTrails said:

In that case i would go ahead and clear the codes. how loose were they? enough to be sucking air around the throttle body?

I feel like it's a possibility-at least two were loose enough that they moved under the weight of the wrench even before I got my hand on good. I just hope it's that easy.

found this over on samarins.com...you guys may already know this but just in case.

Additional trouble codes can shed some light on the cause
Additional OBDII codes that are present along with misfire codes can shed some light on the cause. For example, if you have the P0300 code along with P0171 - System too lean, there is a good chance that the misfire is caused by the lean air/fuel mixture that initially triggered the code P0171. Once the problem caused the code P0171 is fixed, the misfiring will likely go away too.

BlazingTrails said:

Yes and quit cheating on us lol

I just figured I was blowing up the boards over here a lot lately and driving people nuts...had to spread the love. Really though, I do appreciate the help...this truck has been kicking my a$$ lately. On top of work, kids, a school board made up of fools, wife, house and all that other stuff. I got plenty to do. thanks again.

The_Roadie

sunliner said:

On top of working for my wife, fools tearing down the house, a school board made up of kids, and all that other stuff. I got plenty to do. thanks again.

There, I fixed your post. :eek:

The_Roadie said:

There, I fixed your post.

you are correct, sir.

but theriously folks....while it was probably a good thing I checked the throttle body (see previous post)...looks like I didn't really change anything.
took the ol' tub out for a drive. initially the LT trims were down around 4%. drove around town and then got on the interstate for about 15 miles...LT trim back up to ~12-14 %. got back onto the city roads at 30-45 mph and at one glance the trim was 17.5% ,as low as 5% but generally still hovering around 12-14% .

Currently no hard codes (I had unplugged the battery last night) My pending 0300 has cleared, but I do have the 0171 pending, not surprisingly. I've just about exhausted everything I can check or fix...much as I hate it....might be time to pay the man.

and how about the MAF sensor? I cleaned it...but how would I tell if it needs replacing? Getting to the point where I can't afford to throw more parts at the truck...thanks

finally thought to grab the freeze data when the code set...does look like I have a lot of air coming in , if I'm reading this correctly

no....I'm afraid I might find one... :frown: ...but yeah...I need to look. would that manifest as a vacuum leak though? everytime I put a gauge on it, it looks normal.

could be a hairline crack. My good ol' Blazer had a cracked exhaust manifold but that thing was loud as hell. I heard it before it ever cause a code to set. Drove that money pit for 15 years...

Looks like the exhaust manifold is another common weak point on this platform, but I see they're also famous for the bolts backing out (as are the intakes) I know I've been on a rant lately, but does GM ever fix anything?

Guys - I'm new on here and wanted to know if there's a place I can go to get a primer on reading and interpreting the spec values on the OBDII, i.e., the ones in Sunliner's post # 24 above? I've been working on cars for a long time, but the computerized stuff is fairly new - beyond reading the codes. I'm in the process of working through and P0171/P0172. Currently replacing both O2 sensors and contemplating replacing all coils. I have 189K on my 04 4.2L XUV.
Thanks in advance.

Mounce said:

I hadn't heard of the bolts backing out but I've heard many cases of breaking them when trying to take the manifold off.

I guess your first attack should be to pull the heat shield off and inspect for cracks.

Agreed. Gonna go get me a can of PB Blaster...sounds like I might need it.

BlazingTrails said:

well i have 2 scanners but i still do a pcm reset. it resets all of the fuel and timing maps. i use the scanner to clear stored codes.

We speaks tha treuth

Another newbie question - how do you do a PCM reset? Seems appropriate for my situation. Just disconnect the battery for 30 or do I use the scanner?

Thanks - came over here this morning from TrailVoy when I read that most experts there had come over here. This site is a lot more active, for sure!

Thanks! Roger on the TB cleaning - that's on the list for today as well as a fuel filter change.

Anyone have an opinion on whether I should just bite the bullet and replace all the coils (189k)? I've got 'em here and as long as I'm taking everything off to clean the TB, it'd save time.