Need Advise on Code 420.

[2003-4x4runner]

Need advise on code 420. A few months ago my CEL came on and I checked the code to be 420, "Catalytic system efficiency below threshold". So I'm guessing it was a bad O2 sensor. I was going to order a new O2 sensor today but on Friday I noticed the CEL light is no longer on? The only difference I can think of is I just filled up my tank with 76 gas and normally I use Exxon or Shell. Could it of been the gas I was using? The 4Runner has 162K miles on it and it runs great. No issues even with the CEL on and gas mileage never changed. Should I even bother to change the O2 sensor? I know its about time I should, especially with 162k miles on it. How long do O2 sensors last anyway?

 

[RedSled]

Maybe your cap was not on tight?

 

[2003-4x4runner]

Maybe your cap was not on tight?

That was my first thought but it checked out OK. I'm really thinking it was the Exxon gas I was using.

 

[riceandpho]

That was my first thought but it checked out OK. I'm really thinking it was the Exxon gas I was using.

gas cap, i just replaced a new cap since the original got loose too quick and no more tension.

 

[2003-4x4runner]

Well, I spoke too soon and the CEL came back on with the code 420. I'm going to replace the O2 sensor. The 4Runner has 160k on it and it should be replaced anyway.

 

[4Rager]

gas cap, i just replaced a new cap since the original got loose too quick and no more tension.

TIL code 420 most commonly means you were too high and forgot to tighten your gas cap.

 

[riceandpho]

TIL code 420 most commonly means you were too high and forgot to tighten your gas cap.

my cap actually loss tension when unlocking, no more spring feeling.

 

[2003-4x4runner]

So today I replaced the O2 sensor, cleaned the MAF, replaced the air filter and bought a new gas cap for $25.00 from the dealer. I cleared the code did a test driver for about 50 miles and so far so good. I have a long drive tomorrow, so let see if all this helped.