Any way to see if a seller has reset the check engine light on a car?

[daveymark]

Will the folks at Autozone be able to tell me this with their free code checker doohickey??

 

[Imported]

What's wrong with reseting the check engine light? I've done it after a 60k tune up.

 

[OS]

i'm not totally sure, but i think for OBD2 cars it stores recent codes.

 

[amol]

Originally posted by: Imported
What's wrong with reseting the check engine light? I've done it after a 60k tune up.

Maybe they reseted it without doing a tuneup?

 

[Pepsi90919]

yes, it stores the miles/metres since the last reset.

 

[AStar617]

No, there's no way to tell when it's reset, other than the fact that resetting the light without actually doing anything to fix the problem will usually result in the light returning after some driving. My advice: if you have the car to even take to autozone, drive it hard first. Take it out on the interstate and stretch its legs for 15-20min to try to induce any latent problems.

And contrary to what some have suggested, the check engine light doesnt ususally come on for vehicles that simply need a tuneup. Don't confuse the check engine light with one of those service interval lights.

 

[Imported]

Originally posted by: AStar617
No, there's no way to tell when it's reset, other than the fact that resetting the light without actually doing anything to fix the problem will usually result in the light returning after some driving.

And contrary to what some have suggested, the check engine light doesnt ususally come on for vehicles that simply need a tuneup.

When I hit 60k miles, the light lit up. :/ I realize that isn't the case for all cars though.

 

[akshatp]

The "Service Engine Light" is different than the "Check Engine Light"

The CEL will only go away after the problem that it was originally lit up for has gone away.

The SEL will go away after the tech/owner resets it (whether or not the maintenance was performed)

 

[mugs]

Originally posted by: Imported

Originally posted by: AStar617
No, there's no way to tell when it's reset, other than the fact that resetting the light without actually doing anything to fix the problem will usually result in the light returning after some driving.

And contrary to what some have suggested, the check engine light doesnt ususally come on for vehicles that simply need a tuneup.

When I hit 60k miles, the light lit up. :/ I realize that isn't the case for all cars though.

Check engine light = something is wrong that is causing your car to be out of emissions compliance.
Maintenance light = your car needs routine maintenance. Usually based on a certain number of miles.

 

[daveymark]

Sorry I should have been more clear. some unscroupulous sellers will unhook the battery, this will cause the check engine light to dissappear until the car has been driven for a little bit, as unhooking the battery resets the computer.. I know that emissions centers will know if this is done, so I'm wondering if there's a way for the average joe to know if and how it's done..

I live in a state where emissions testing and passing are required in order to drive

 

[Imported]

Guess I was wrong. I never paid attention.

 

[QED]

Originally posted by: daveymark
Sorry I should have been more clear. some unscroupulous sellers will unhook the battery, this will cause the check engine light to dissappear until the car has been driven for a little bit, as unhooking the battery resets the computer.. I know that emissions centers will know if this is done, so I'm wondering if there's a way for the average joe to know if and how it's done..

I live in a state where emissions testing and passing are required in order to drive

Are you just worried about it passing emmisions?

If so, just have him get the test done BEFORE the title is transferred-- it's something that will have to be done anyway.

 

[Triumph]

The reason emissions places know that you reset the CEL is because they are looking at much more information than the Autozone scanner can tell you. All that machine does is tell you error codes. There are about 8 blocks in your computer called "Readiness," they are data logs of certain functional checks the car must do to make sure the emissions equipment is working. They are things like front/rear O2 sensor, catalytic converter, secondary air system, a few others that I don't remember right now.

When you take your car in for emissions, the first thing they do is check these banks to make sure that the car's emissions systems are functioning. When you reset the computer (by clearing any codes), these readiness blocks are reset as well and your car will not have had time to check them out; typically it takes a couple days of driving to fully check out these functions (the cat for example needs to get really hot for the car to check its functionality).

The Autozone tool can tell you error codes ONLY - these error codes are mandated by the EPA on all vehicles since 1997. They are primarily emissions related but can sometimes relate information about other associated issues. But they are a very rudimentary check - a real scan tool can tell the mechanic much more about the car than the free Autozone hand tool.

 

[j00fek]

you cant reset the light, itll go away when the problem has been fixed.

 

[BoomerD]

As a rule, just unhooking the battery WON'T fix the check-engine light. Doesn't matter if you leave it unhooked for days, as soon as you start the vehicle, it will come back on, unless you've fixed the problem that caused it in the first place.

 

[daveymark]

Will a mechanic have the proper scanner for this? to tell if the banks have been reset?

 

[Triumph]

Originally posted by: daveymark
Will a mechanic have the proper scanner for this? to tell if the banks have been reset?

Yes, any pro mechanic shop should have that. Maybe not an oil change place, but a real mechanic.

What exactly are you trying to do? Cheat your way out of emissions? Or check on a car that you are interested in buying?

 

[daveymark]

Originally posted by: Triumph

Originally posted by: daveymark
Will a mechanic have the proper scanner for this? to tell if the banks have been reset?

Yes, any pro mechanic shop should have that. Maybe not an oil change place, but a real mechanic.

What exactly are you trying to do? Cheat your way out of emissions? Or check on a car that you are interested in buying?

check on a car I'll be interested in buying. I wonder if I might be able to take the car to the emissions testing facility and just have them check it for free

 

[daveymark]

looks like I can have the test done for $20

Text

might just be better for me to go to a regular mechanic and have the car checked out comprehensively

 

[BoomerD]

BTW, the check engine light merely warns of emmision related problems. Bad O2 sensor, or some other thing in the emmission control system. It CAN signal engine problems, IF they're severe enough to affect the pollution levels going through the exhaust system.
Having that re-set is usually a sign that the appropriate repairs were done, otherwise, the light would just come back on, the next time the engine was started.

 

[daveymark]

Originally posted by: BoomerD
BTW, the check engine light merely warns of emmision related problems. Bad O2 sensor, or some other thing in the emmission control system. It CAN signal engine problems, IF they're severe enough to affect the pollution levels going through the exhaust system.
Having that re-set is usually a sign that the appropriate repairs were done, otherwise, the light would just come back on, the next time the engine was started.

in my experience the light comes back on after a little bit of driving. Not too much driving, but likely more driving than a test drive.

 

[kami333]

Originally posted by: daveymark

Originally posted by: BoomerD
BTW, the check engine light merely warns of emmision related problems. Bad O2 sensor, or some other thing in the emmission control system. It CAN signal engine problems, IF they're severe enough to affect the pollution levels going through the exhaust system.
Having that re-set is usually a sign that the appropriate repairs were done, otherwise, the light would just come back on, the next time the engine was started.

in my experience the light comes back on after a little bit of driving. Not too much driving, but likely more driving than a test drive.

Same here, it's usually a combination of starts and miles (for the different sensors).

Checker's OBD scanner will show how many of the sensors are "unready", which can give you an idea if it was reset or not. Depends on your state but you can have a few unready codes and still pass, that's how I got through mine (bad cat, needs to be replaced).