OT - Check Engine Lights, Computer Codes and Passing Inspection

[DerbyDad03]

I asked 5 different "experts" the same question and got 3 different answers.

"If a vehicle has an intermittent Check Engine Light from an Evap code, and the light is off when the vehicle gets inspected, will the inspection computer still pick up the code causing the vehicle to fail the inspection?"

For those that don't know, Evap codes are the codes that would come on if the gas cap was loose or the gas tank fill tube was cracked, etc. Any leak in the fuel system could cause an Evap code.

A well known auto parts store and a local service station both said it's hit or miss, you never can tell if it will pass.

A different well known auto parts store and a local service station where a huge part of their business is "instant inspections" but that also does repairs, both said it will definitely fail.

A third local service station (a big, always busy operation) said if the light is off it will definitely pass.

What do you folks think?

[philoÂÂ]

The light will come on if there is an error condition

so if the light is off when the car is inspected it should pass.

(Obviously not true if there is a lose connection to the bulb, but that is not likely to be the case)

[Retired]

When I use my own code reader on my 1994 Olds or the 1994 GMC Jimmy, it reads out both *current* codes, and *history* codes. The history codes stay until reset using the code reader.

So it would seem possible if you have stored history codes, the inspection just might pick up on them, whether the lite is on or not.

[DerbyDad03]

That's what the people who said it would "definitely fail" said. They said the codes would still be in the vehicle's computer history and the inspection machine would pick them up.

Once we get a few more answers/opinions, I'll post the results of a real life situation.

[philoÂÂ]

What if rather than being an intermittent problem...you found the actual cause and fixed it? The car is now fixed, but the previous codes are still in memory. Why would they fail you? Basically the car either passes or fails, I don't see what prior history has to do with it.

A friend of mine has been trying to get her car passed for five months. She recently had a good day and finally got it passed. She lucked out...but still all the previous error codes must have still been there.

Guess you will know when you get there.

[Gordon Shumway]

That's a good point. In that scenario the car would have to pass.

Or as a lawyer might say, "Objection! Prior bad acts are not admissible and would be prejudicial."

I'm not a lawyer but I watched one on TV.

[Tony Hwang]

Hi, That is how it works. Old code is stored in the memory until cleared. And OP, gas tank cap might be faulty. I'd connect the code reader and clear the memory B4 going in for inspection. My code reader is a laptop with OBD II utility software. I built a USB 2 interface kit and got a copy of software from eBay. Just code reading simple ones are freeware.

[gfretwell]

I thought if you disconnected the battery it cleared all the codes. Do it down the street from the inspection center and hope you don;'t have a failure before you get there.

OTOH if this is "history" you can always say that was a long time ago and you had that problem fixed. They can only fail you on an existing condition.

[cjt]

I think it could depend on what state, and what county within the state, you are in.

[micky]

That's my understanding too, except the code also disappears if the problem is gone after 100 turns of the key to Start or On, not sure which.

So if Phil's friend drives every day that's maybe 5 days after the last visible light. Well, he didn't say how much the light was on.

[Erik]

Was anything said about 'readiness monitors'

More here:

Yea, I know this is from NY, but it's much the same song/dance anywhere emission testing is done.

Disconnecting the battery, or code clearing resets the things, some of which take a few days and some driving to 'reset'

Erik

[clare]

Don't know about where you are, but in Ontario you can have one monitor not set and still pass as long as the light is out and no code. If the monitor sets and the light comes on before the test is done, you are out of luck.

If you have 2 or more monitors not set, it fails - period - light or no light - code or no code.

Evap is one of the monitors, and to be sure the monitor will not set, keep the tank below 1/4 tank or over 7/8 because the monitor cannot set under those parameters..

You need to make sure the other monitors all set or it WILL fail. A good scanner will tell you if the monitors are set

[clare]

It won't pass if the monitors are not set - that's how they know if the codes have been recently erased.

[clare]

I am a licenced auto mechanic.

If you erase the codes the codes are gone - period. The code reader reads current codes and "incipient" codes. To turn on the light and "set" a code the error must be found a certain number of times in a given time period. Untill that happens they are "incipient" codes. Before a code can be set, certain conditions need to be met to set the "monitors"that monitor the sensors. Until the monitor is set, the computer cannot set a code or even an incipient code. A drive cycle needs to be run through to set the monitors - and if you keep certain parameters outside the boundaries required to set the monitor you can reset all the monitors EXCEPT the evap monitor if you want to. If your test allows one monitor to be unset and still pass, you can pass with bad evap. If you run the drive cycle with wrong temperatures, or the tank too full or too empty, the evap monnitor will not set.

[clare]

If the problem is fixed and the codes are not erased it will not pass. If the codes are erased and the monitors are not reset (drive cycle) it will not pass. The E-Test as it exists in Ontario, anyway, is a farce

I can tell with 99% certainty if a car is going to pass, in about 10 minutes.

[clare]

If you reset the codes just before going for the test I can GUARANTEE the car will fail. 100%

[clare]

Not true. If you disconnect the battery on an OBD2 vehicle the code stays. Period. If the light goes out and a history code exists - you fail. If you clear the codes just before testing - you fail.

They CAN fail you for conditions that do not exist at the moment - it needs to pass all required tests - in Ontario that means you can have one "monitor" unset - but not two. Not sure if all areas allow that one "grace" monitor. Resetting the codes unsets the monitors

[Larry W]

Your 1994 Olds or Jimmy sligthly predates OBDII which requires predates certain behavior, FWIW, but consider this. Say the vehicle does have a history code, to use the OPs example an evap code, and it was caused by a defective gas cap. So if the OP replaced the gas cap, fixing the problem, should the inspection then fail because of a history code that predated the fix?

Just askin...

[trader4]

I think the answer is that it depends. If you fixed the gas cap and drove 2 miles over to the inspection station, then it will surely fail, because the computer doesn't know it's been fixed. When the computer first notices something wrong like this, it records it as a "pending" fault. If the condition persists long enough, then it sets an actual fault code and may also turn on the check engine light, depending on what the fault actually is. In the case of the leaking gas cap, it would turn on the check engine light.

Usually, the fault would get cleared manually when the problem is identified and fixed. If it's not cleared manually, then I believe the computer would clear it eventually, after it's seen it being normal for a certain period of time. Not sure about that last part though. I do know that the evap system takes a much longer time to accumulate data than many of the other parameters. If you clear/reset all the monitored data, to pass inspection, the car has to be run/driven enough to set all the necessary monitors. The evap system one is the last to get set. I've seen discussions an no one seems to know for sure what it takes to set it, ie is it engine running time, distance driven, startup/shutdown cycles, etc.

In the case in question, if it were me and the immediate objective was to get it through inspection, I'd just hook up my code reader, clear the code, and take it to be inspected before it came back on.

[trader4]

As CL stated, that's likely a guaranteed failure. The emission testing they do uses the data from the computer. They aren't just looking for the check engine light to be on, or for fault codes. They are looking for data that affirms the car emission system is working correctly. Specifically, they look for a list of emission monitors that must be set by the car computer, which says they are OK. When you clear the computer, those all get cleared and the car must be run/driven for some period of time before they get set again. Some get set within mins. Some, like the evap system one, can take hours or a day of two to get set. I think here in NJ they allow you to still pass if one of those is not set. But if you clear them all and drive a mile to get it tested, almost certainly it will fail.

I don't think any stories are going to have much effect, nor are they needed. As you say, they only fail you for an existing condition. And if the puter says it's not right, I don't think any stories are going to prevail.