Check Engine Light - Automatic Reset?

Does the check engine light go out on its own, or do you have to clear it manually? I have the dreaded P0420 code, and among other things, poured in a bottle of Cataclean in the gas tank, hoping that the light would eventually go out after some driving, so I can pass my Calif smog check. So far, it's been a couple of hundred miles and the CEL is still on and now I'm wondering if I have to manually clear it with my Ultragauge and then go through a drive cycle? This is for a 2000 Tacoma Pre-Runner (3.4L).

 

It'll take days to reset. Just do it manually.

 

it depends, if you correct the issue that caused it or if it was a false trip, then most CEL codes will reset after a few drive cycles showing normal readings again but not all codes will reset. certain codes are deemed as critical items don't reset so it makes you find out why it tripped in the first place. I can tell you that I personally see faulty o2 sensor codes will reset on their own after its replaced.

 

loose gas cap resets after a short drive..

 

o2 light will reset once you change the faulty sensor..

 

i have the same code (catallitic efficiency below threshold) come up regularly and it also randomly goes away -sometimes days sometimes it takes a month -once it took 2 months...

i tried cataclean also... CEL went out on its own- but the light has come on and went out on its own a few times now and i have not used cataclean except for the first time it pulled the code.

on a side note; i replaced (6 months ago) the front o2 sensor and not the rear o2 sensor and so the minor difference in the amounts of deposits and gunk on the two o2's is likely skewing the measurements and triggering the code via. the discrepancy's between the 2 readings of the o2's before and after the cat's ...

 

the other option is to disconect the negitive terminal on the battery for 5 min or so the day before the smog inspection and finger's crossed

 

Its not impossible for the cat to go bad but more likely the O2 sensors...Id definitely change them first before a cat..

 

That won't work as the readiness monitors will indicate NOT READY, unless you've completed the drive cycles for each monitor. You will flunk smog check automatically. In my case, there are four that have to be completed, which as I am finding out, can take a number of days of driving!

 

If the Cataclean doesn't work, then replacing the O2 sensors is my next step. I hope it doesn't go beyond that, as cat converter is probably the next step! $$$

 

guess california is stricter than pa was... currently living in a no inspection state tho is awesome! well the consequently low speed limits aren't but it is nice overall...

 

cali spec cats are not cheap... i looked into it when my code came up a few times and was like 2x and up what a non ca-spec universal cat is...
shop around for the o2 if you do need one -and as a tip our trucks are fairly picky about sensors so its best to stick with OEM denso's for the o2 and MAF at least... i got mine for about $85 but i have seen them go for significantly less online.

 

just bought my rear o2 for $50 on Amazon for a denso...truck is an 04

 

Update: Its been 200 miles since I added a bottle of Cataclean to my gas tank and reset my CEL manually, and so far the P0420 code has not shown up, so I am hopeful that that may have solved my problem (at least long enough to pass my long overdue smog test). However, I still have one readiness monitor that is Incomplete (Catalyst Monitor). Based on past history, I expect it complete any time now.

However, about a hundred miles ago or so, my CEL came on. I checked the code and it was the P0120 (TPS A Circuit Malfunction) which has surfaced occasionally during the two years I've had the truck. I decided to just go ahead and purchase a new TPS (found a new OEM TPS for only $26!) to hopefully solve that problem once and for all. I have received the new TPS but have not installed it yet. Well, a couple of days later the CEL went off on its own without me doing anything (except more driving). But when I checked with my OBD-II scanner, it showed that the P0120 code is still stored in the ECM. So, I have two questions:

1) Will the P0120 code currently stored in the ECM go out by itself, and if so, under what conditions, and how long should it take? I could clear the stored code with my scan tool, but then I'll have to start the lengthy drive cycle process all over again. So, I'd rather not do that (I'm already overdue for my smog check, and got a fix-it ticket for having an out of date registration).

2) Is it necessary to have all stored codes cleared before you can pass a smog check? I know a lit CEL is an instant fail, but not sure if all stored codes have to be cleared.

Thanks in advance.

 

I sure feel sorry fur you cali boys. You guys gotta put up with so much state bullshit! Its a real headache and can in certain situations really cost alot of fuckin coin just to pass some stupid ass test. I bet the cali law book is four feet thicker than most other states, especially the west coast states.

 

Yeah, it sucks. Though I have to admit that emission standards have made a big difference in the ambient air pollution in the state. LA smog was pretty disgusting back in the 1970's, and its much, much better now. But, yeah, I think CA goes overboard with testing and requirements. One thing we don't have here is vehicle inspection requirements for registration. If we had that, plus emissions testing, I think everyone would leave the state or get rid of their cars...too expensive!

One thing I can say is that two bottles of Cataclean seems to work, as others have claimed. I still got the P0420 code after one bottle, but so far I've gone 250 miles without a P0420 code after the second bottle. Longest I've gone that far since I bought the truck. Still haven't cleared the Catalyst readiness monitor though. Got my fingers crossed, and still hoping someone can help out with my questions above.

 

Im actually really suprised you guys dont have vehicle inspections! Hell even Utah has them...

 

If it was me I'd install a new O2 sensor along with a URD O2 simulator. You'll most likely resolve your P0420 for good and still be able to pass emissions. I've got the Cali truck as well but live in Montana. Have my 2nd CAT removed installed a new O2 sensor and URD simulator. No further issues. Just a suggestion.

 

I'm almost certain simulators cause and instant smog check failure...there may even be a fine. They inspect all emission components.

 

Back from the dead!

Having some SMOG issues, so I thought I'd chime in as I learned something at the SMOG shop this morning...

1) No, I don't think the P0120 will ever clear itself. I had one that was still stored after several weeks, so I had to manually reset it. Also, I had the same thing happen with an automatic transmission code, was in there for over a month, long after the CEL had 'cleared' itself.

2) Yes, in my limited experience, if there is a code stored on the ECM, you will not pass smog.


Question- How long is the lengthy drive cycle before the ECU is no longer "not ready"???