# Car engine light on; mechanic can't find anything wrong
**URL:** https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388
**Category:** In My Humble Opinion
**Created:** [March 3, 2007, 2:34am UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388 "2007-03-03T02:34:31Z")
**Posts on this page:** 9
**Page:** 2
### Author:  [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)
#### Post date: [March 3, 2007, 4:27pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/21 "2007-03-03T16:27:14Z")
Both my wife and I had cars where the check engine light came on with no discernable cause and repeatably did so. The sometimes draconian Massachusetts annual inspections do not consider check engine lights to be disqualifying if that gives you any comfort.
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### Author:  [@Joey\_P](https://boards.straightdope.com/u/Joey_P)
#### Post date: [March 3, 2007, 4:32pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/22 "2007-03-03T16:32:39Z")
[QUOTE=Boscibo]
Wisconsin doesn’t have smog tests. The gas cap thing was brought up in our case too, but after every tank it comes on, and yes we do make sure the cap is on tight.
[/QUOTE]
We have emissions tests, but the check engine light being on is an automatic failure.
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### Author:  [@Hanna](https://boards.straightdope.com/u/Hanna)
#### Post date: [March 3, 2007, 4:39pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/23 "2007-03-03T16:39:09Z")
I have never had to undergo an emissions test in Wisconsin. I’ve lived here since 1989. Maybe in the larger cities you do?
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### Author:  [@Joey\_P](https://boards.straightdope.com/u/Joey_P)
#### Post date: [March 3, 2007, 4:52pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/24 "2007-03-03T16:52:22Z")
[QUOTE=Boscibo]
I have never had to undergo an emissions test in Wisconsin. I’ve lived here since 1989. Maybe in the larger cities you do?
[/QUOTE]
Wow, I never new that, but, yup, you’re right.
[http://www.dot.wisconsin.gov/drivers/vehicles/im.htm](http://www.dot.wisconsin.gov/drivers/vehicles/im.htm)
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### Author:  [@Hanna](https://boards.straightdope.com/u/Hanna)
#### Post date: [March 3, 2007, 4:57pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/25 "2007-03-03T16:57:59Z")
And I never knew that there are some places in WI that have to undergo that. I know MN does - I went with my Mom once when she had to get hers done.
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### Author:  [@NajaNivea](https://boards.straightdope.com/u/NajaNivea)
#### Post date: [March 3, 2007, 5:37pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/26 "2007-03-03T17:37:07Z")
My car’s check engine light has been on since shortly after I bought the thing, five years ago. I’ve had four different mechanics check it out at various points over the years (Five, if you count the one who wanted to charge me $180 _just to run the diagnostic computer check_. He never actually touched the car, though.) and none of them have ever found anything amiss. Kinda defeats the purpose of the thing if it’s always on and consistently ignored.
I’m good friends with my mechanic and have always been very, very good about keeping up with routine maintenance and regular service checks. It runs as nicely as it did the day it drove off the lot and couldn’t be in better shape. Who knows?
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### Author:  [@IvoryTowerDenizen](https://boards.straightdope.com/u/IvoryTowerDenizen)
#### Post date: [March 3, 2007, 5:53pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/27 "2007-03-03T17:53:02Z")
[QUOTE=SylverOne]
FYI - my check engine light will come on if my gas cap isn’t tightened down all the way.
I know Chevy and Chrysler do this… not sure about Hyundai, but it’s something to check.
[/QUOTE]
Honda, too. I have to tighten the cap until it “clicks” three times.
My light will go on for scheduled maintenance, as others have said. I take it to the dealer for those check ups, so I don’t know if regular mechanics can make hte light go off after a check up.
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### Author:  [@Joey\_P](https://boards.straightdope.com/u/Joey_P)
#### Post date: [March 3, 2007, 6:11pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/28 "2007-03-03T18:11:12Z")
[QUOTE=IvoryTowerDenizen]
Honda, too. I have to tighten the cap until it “clicks” three times.
My light will go on for scheduled maintenance, as others have said. I take it to the dealer for those check ups, so I don’t know if regular mechanics can make hte light go off after a check up.
[/QUOTE]
Since OBDII is a standard, anyone should be able to turn it off. Including yourself if you buy a OBDII scanner. But I wouldn’t recommend turing it off unless you know what you’re doing.
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### Author:  [@IvoryTowerDenizen](https://boards.straightdope.com/u/IvoryTowerDenizen)
#### Post date: [March 3, 2007, 6:12pm UTC](https://boards.straightdope.com/t/car-engine-light-on-mechanic-cant-find-anything-wrong/394388/29 "2007-03-03T18:12:32Z")
[QUOTE=Joey P]
Since OBDII is a standard, anyone should be able to turn it off. Including yourself if you buy a OBDII scanner. But I wouldn’t recommend turing it off unless you know what you’re doing.
[/QUOTE]
That’s good to know- thanks! I wouldn’t turn it off myself because I thought it was just time for a check up- I’m sure that would be a karmic signal for my engine to explode. 🆒
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