resetting OBD-II

I have a 2003 Pontiac Vibe. The check engine light came on, but went off after a week or so. I am pretty sure that it was due to me not tightening the gas cap to a satisfactory degree. The problem is I am off work today and want to take for emmisions inspection. I want to clear the codes so I pass the test. Can I just disconnect the battery for 1/2 hour, or was that only OBD-I?

If it is not faulting right now, then it already reset.
Defaulting your computer would place you in a ‘not ready for test’ state, which is not what you want.

I thought that it stored codes for a certain number of key turns. What I think you are telling me is that if it is off, it has already cleared itself. Is that correct?

You understand me correctly.
The fact that it stores codes, which it does, will not stop you from passing your test.
I’ve seen stored codes that were 2 years old still show up in memory, but they didn’t interfere with my emmissions testing.

OBD II systems have the ability to turn off the light and delete codes for an intermittent fault.
The criteria for such actions varies from car maker to car maker, and may vary from code to code, or from year to year.
If the light is off now, you should be good to go for your emissions inspection.

slight hijack - My son’s car has a cheapo catalytic converter that was put on it when he bought it. The "check engine " light came on a few months after purchase and he was able to read that it was a catalytic converter code. I’ve since talked to a few mechanics who all agreed that the fact that it was a generic converter and an older engine the o2 sensor was probably reacting at too tight of a threshold level. In other words, the car isn’t polluting all that much but the sensor is triggered. The car runs fine, no apparent damage to the CC. I’d like to reset the threshold of the sensor and reset the alarm. My questions are

1 - Is this legal for me to do it?
2 - If it is will I be able to do it with commercially available hardware/software or do auto manufacturers not make their code reset techniques available?

Almost certainly not.

You’re not talking about a code reset, you’re talking about reprogramming the onboard computer. I seriously doubt you could affect this parameter, and if you could I would expect the necessary equipment to cost thousands.

Thanks Gary, but is your reply that it’s not legal based on anything other than your opinion? Your help is appreciated but I want to know if its fact or opinion.

If the car is still environmentally legal then possibly resetting the code is not a problem. One mechanic I’ve talked to told me that the mechanics at a dealer in town were adjusting the tolerance of the car’s computer alarms to accommodate slightly higher (but still within acceptance) exhaust temperatures because the rings on the older cars let out a little more heat. This was for a brand of car different than my son’s.

And I know that I could go on line and buy hardware that interfaces between my car and my laptop and perform diagnostic tests. That interface is the same interface used by mechanics.

The “check engine” light on my son’s car came on right after he washed the car on a very hot day. We suspect that highly humid air going through the engine may have set off the sensor and quite possibly it remains on (even though it is no longer out of bounds) until it receives a reset code.

My question was - Is there a legality which keeps me from performing the reset and is the reset code available?

I see from your location that we are neighbors so maybe you know for certain how this is applied in Missouri.

I suspect you are correct about reprogramming tolerance levels but as a first test I 'd like to clear the code and see if it returns.

I don’t want to go to an honest mechanic and pay him $X just to reset the code and I very much don’t want to go to a dishonest mechanic and have him tell me I need $XXX in repairs if all I need is to reset the code and have my son avoid car washes on 100 degree days.

Unless the mechanic tested the car on a dyno running while loaded, there is really no way to be sure that the converter is doing its job while you are driving. I can name you many cars that when you stick a sniffer in the tailpipe run clean as a whistle. Put them on the dyno and the truth comes out. They are pigs and fail big time. With no load the emission control system has to barely function to clean up the exhaust. I smogged cars where the owner told he had hollowed out the converter. Due to the way the question was worded on the visual inspection I could not fail them for that (Is the converter connected and appear to be working?) When I got the tail pipe reading, it was high but still within standards. These people got a huge shock when loaded mode testing came in and all of a sudden their car failed.
I have heard of generic converters that will get you though a single emission test, and by the time the next one is due, you will need a new converter. While I don’t if this is true, I have heard it from enough different guys who know what they are talking about, that I tend to believe it.*
As far as reworking the computer goes, I doubt you could do it yourself. Yes technicians often reprogram computers. What they are doing is installing a new program provided to them by the car maker. That program is most assuredly legal.
Either that or they are installing power chips. Depending on where you live a power chip may not be legal to install.
I doubt you will find any power chip programs that re-work the parameters for the rear O2 sensor.
A new factory converter is by far and away the cheapest permanent, legal fix for your problem.

*Like on this message board, if QED, Stranger, and Una all told me something was true, I would tend to believe it.

I took it that you were referring to this: “I’d like to reset the threshold of the sensor…”, which would require altering the computer’s program. I do not know with absolute certainty, but my understanding is that it is a violation of EPA regulations for a shop to do this (BIG fines), other than factory-approved updates. It might not be a violation for an individual to do it.

If by reset you mean erase the trouble code memory and turn off the “Check Engine” light, that’s perfectly legal. There’s no reset code, it’s just an operation that’s performed. You can do it with a scan tool, probably do it with an inexpensive code reader or with the cable and software you can buy on the net (verify this function before buying), and on all the vehicles I’m familiar with do it by disconnecting the battery*. Then the question is how soon will the problem set the code and activate the light again.

I don’t know what laws MO might have about reprogramming, what I see discussed in the trade are Federal laws and regulations.

*On some cars just disconnecting the battery for an instant will do it. On others, the instructions are to leave it disconnected for a certain length of time, touch the positive and negative cable ends together (while it’s disconnected), or press on the brake pedal (while disconnected).

You know, if it IS legal for a vehicle owner to do so, it would probably be easier to simply engineer a modified CO2 sensor than to change the value in the computer.
The output on those sensors is pretty simple, electronically.

(Bolding Mine) That’s exactly why I wanted to reset the code. Some of the internet discussions I’ve read seemed to indicate that temperature plays a big role in the generation of an error code. As the valves and rings weaken in older cars more heat gets passed into the exhaust. Too much heat=ruined Cat converter. The sensor is there to warn you that damage is/will occur to the converter.

So I considered the possibility that the steam going through the system (old car + car wash+combustion+extremely hot day+ city traffic driving) was just enough to set off the sensor. I want to reset it to see if it goes off again or if it was just a one time occurrence.

Thanks again for sharing your knowledge.

That’s needless.
If the problem pops up again, so will the error.

What’s needless? Determining whether the condition is permanent or intermittent?
My wallet disagrees.

Right now the check engine light stays on -all the time. I have no indication whether it’s on because a problem still exists or whether its on because for a brief period of time it exceeded its threshold.

If the problem is intermittent and I have the means to reset it myself, I’ll just do so when the problem pops up.

If its permanent then I’m looking at engine work and possibly a new converter.

My apologies. I confused you with the OP; his CEL has been resetting while yours hasn’t.

Whoops! Scratch that.
If the problem occurred and then just went away, your light WOULD have cleared within a few days.
You still have the problem.
Now if you’re curious how LONG it would take you to have that same problem again, then that may, perhaps, be a valid diagnostic heuristic.

Not necessarily. In some cases, the light won’t go out until there have been, for example, 50 consecutive restarts without the problem evident. In other cases, the light will not go out by itself at all. It varies depending on the type of car and type of problem.