I have off and on read about OBD2 over the years -- and the information you can usually find is so vague, it drives me a bit nuts. I'm sure that the guys here who do this for a lliving actually do know most of the answers, but it's not clear to me where to find them.

I gather that OBD2 means that there are monitors running when you're driving. Some of them are continuous and some are intermittent. I don't know that I've ever seen the complete list of which is which.
You can hook up your scan tool and request a Parameter ID (PID) -- which should give you the status and any data from that monitor. OK so far I guess.

Now if something goes wrong, it can
1 set a code and turn on your light
2 set a pending code and not turn on your light, but your vehicle might run somewhat crappily

pending codes can be set if it's not considered too serious( I think) or if it will take 2 'trips' with the same fault to set the code.
(2 trip codes also require 2 trips to clear)

Clearing codes will only work if the code does not set again the next time you drive.

Some codes can't be cleared until the vehicle is run in the correct 'trip' and the problem does not occur.-- they're called permanent

I think that's right, but I've just read pages of blather to get this close.

Notice that I don't have any specifics on code setting and clearing -- information seems to be in short supply.

Clearing codes can be done with a 'trip' that meets requirements, but I did read a Chilton's Emissions manual that said that the 'trip' s were different depending on the fault.

Also, some codes can be set because a different fault keeps other monitors from running (again, no details seem to be readily available).

Maybe the pros here are just laughing because they know where all of this info is. Even the stuff that says how obd2 rules changed over the years.

If anybody knows where this info exists in some concise form -- I'd really like to hear about it. Also mention if it's only available if you're willing to spend big $$ -- I have a small limit on that .

Kind of a rant and kind of a request for info.

Thanks,

hj

 

you have soft codes. these are ones that are not an issue to the running of the vehicle, but should be looked at because they may become an issue down the road.
them you have hard codes that will instantly turn on the check engine light.
these will effect how the vehicle runs and need to be fixed asap.

then you have historic codes.
these are codes that are recurrent and you have to run through a drive cycle to get rid of once the problem is fixed.

that is about the extent of my DTC knowledge.

 

You are somewhat right but barely. When the ECM sees a fault, mostly emissions related it flags a code and turns on the check engine light, CEL For the remainder of this post. The light will remain lit until the fault is repaired. You can clear the code with a scanner but if you didn't fix the issue the CEL will illuminate again.
you should be able to find in depth information and explanations at cal.bar.gov or whatever website the local bureau of auto repair has in your area. Also can check the ASE, Automotive Service Excellence, or the society of automotive engineers, SAE.
GOOD LUCK this is some heavy reading when you find it.