How long can it take for engine sensors to gather enough data?

My understanding of the process is this: The computer that assesses the check engine light just tells the mechanics what system is faulty. It may be more targeted than that, but at least sometimes isn't much more tuned. So, there's a little artistry in interpretation by the mechanic. My car was stalling in humid/rainy weather. One shop ran the diagnostic and checked the distributor and found it was wet inside (BIG puddle). He dried it out, but in humid weather the car was still stalling. I brought it to another garage and that guy got the same message from the diagnostic machine, but found that the wires to my spark plugs were also exposed to the humid air. Once he fixed that, all was fine.

Not sure all that answers your question.

when I had emission sensor problems 6 months ago my mechanic told me that the longest it takes for the computer to reset to current conditions is the next start.

It's not just mileage driven, it's also throttle position etc. To make sure the ECU is up to speed (pun) run your vehicle at all throttle and gear settings (well all the throttle / gear settings you can practically manage).

That being said, 200 miles should be more than enough to cover the needed conditions, however it will no harm to run through all the throttle / gear settings you can practically manage.

That contradicts what my mechanic and the state inspection guy told me.

Now, the check engine light came back on after replacing the first sensor, so the computer was able to immediately determine that there was a problem. But the sensors have to gather enough data before the car can pass inspection.

So maybe 60 miles of city driving will take care of it, but 200 miles of highway cruising will not?

I'm just getting my feet wet with OBD2 again, but my experience is several cool down and run periods at least to gather enough info.

I have been chasing a bug in a 2001 Durango, and it takes a couple days to reset the code.

Firstly Rock is wrong as to "several cool down and run periods" per se.

The data needed to confirm full status is not solely dependent on "several cool down and run periods" as discussed it must include certain throttle settings, engine load etc. The ECU needs all operations for given parameters, again some of which I've discussed and advised you as to how to facilitate.

Also your mech is a dork because he should know it's possible to avoid all this hassle and "tell" the ECU in advance that all parameters have registered. Dealers are cool in this regard!

Understand also that I said "200 miles should be more than enough to cover the needed conditions, however it will do no harm to run through all the throttle / gear settings you can practically manage."

Understand also that it's not mileage per se, it's the requisite variances as sent from the sensors that the ECU needs.

Having said all that, if I was to guess as to the source of the problems, and if the ECU, and wiring, and fuel delivery, and catalytic converter, and ignition system etc are all fine - and you run through all settings as I've advised - then some sensors have either not been installed correctly or have failed.

Wouldn't the computer mark the sensors as failed, then?

Well, it's had that. I'm just trying to figure out what I need to do to get the damn thing to pass inspection....

That depends what you mean by "failed" (too vague) because until all required parameters have been sent by establishing all running conditions, things won't be normalized. Error codes prior to normalization are not overly meaningful.

Run the vehicle as I've suggested (or get someone who knows what they're doing to set the ECU) and then report the remaining specific codes (if any).

I have a laptop-based OBD2 reader that can do real-time data-logging, that's a cool way to approach these problems.

The mechanics just reset my car's computer and all is on "okay" again.
(My temperatre sensor was fitted two weeks ago: the computer got the correct data within seconds after the engine started.)

There are different definitions of the word "reset" as it relates to the ECU!

One definition is removing the power (or resetting) the ECU long enough for it to go back to its default settings. After which it must regather all parameters before the CEL will extinguish.

Another definition is sending the ECU data that all parameters are OK, this is typically done by mechs at a dealer. After which the ECU need not regather all parameters and the CEL will not light up (unless there is a recurring problem).

Here is the unit I use

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cost?

There are cheaper gizmos but real time data logging can be very helpful.

US $194.95

http://cgi.ebay.ca/A-302-Windows-Scan-Tool-Scanner-Auterra-OBD-II-OBD2-2_W0QQitemZ320360753482QQcmdZViewItemQQptZMotors_Automotive_Tools?hash=item320360753482&_trksid=p3286.c0.m14&_trkparms=72%3A1215%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318

The computer reports two sensors as "not ready". There are no error codes. In Texas, if two or more sensor report "not ready", then the car does not pass inspection.

Well unless you have a decent OBDII reader you cannot know if there are stored codes or not. Understand that the dashboard CEL is not a tell-all indicator by any means.

Here in BC we have "AirCare " and thus a strict ritual of OBDII educated inspectors reading both stored and active codes.

I don't know exactly what you mean by: "The computer reports two sensors as not ready" however I assume this is something your mech told you but I have no way of knowing exactly how he obtained that information, nor how accurate it is in this specific context, nor what reader(s) he used, nor how educated your mech is in OBDII diagnostics etc.

Again.........having said all that, if I was to guess as to the source of the problems, and if the ECU, and wiring, and fuel delivery, and catalytic converter, and ignition system etc are all fine - and you run through all settings as I've advised - then some sensors have either not been installed correctly or have failed.

that's about what the one I am looking at buying costs, but it does not require a laptop.

(my laptop is more trouble than its worth anymore...)

Then you have to decide if the one your thinking of buying can perform all the tasks you want it to as compared to the Dyno-Scan for Windows.