So I popped a CEL yesterday afternoon. Had it pulled today at Autozone - don't remember the code, but it was the 1st O2 sensor.

When I got home, I popped the hood (was going to reset CEL to see that it would come back on), and noticed that something was very very wrong. What's missing here...would it explain the O2 sensor CEL, or just something else I have to fix?

 

That is your oil filler cap. I'm surprised your truck would idle without it and probably runs poorly. Check your oil and do not operate until replaced.

 

Sure looks like your engine oil cap.?

 

Beat me to it!

 

quite possibly . . . I suggest ->oil cap removed, runs wierd

 

I thought it was called a diff breather

Your kidding you dont know what that is right???

 

I knew what it was, but was honestly wondering if there could be a connection between this and the O2 sensor code.

I'm surprised the truck ran alright without it. Just got back from a weekend camping trip in Maine (3 hours each way). Got decent gas mileage, too.

 

I could see it affecting it because the engine runs off vacume and its letting in air past the MAF thus the O2 and the comp is freaking wonderings whats going on. Its going to affect the A/F ratio because the MAF is telling it one thing and the O2 another. Im suprised you didnt pop any other codes. I would get a new cap and clear the codes and it it comes on again then go from there

 

Replace cap, unplug battery to reset computer, wait and see if the code comes back. Oxygen sensors do go bad even on a Toyota and it might help your gas mileage to get a new one.