# trouble codes mystery



## 3onthetree (Dec 7, 2018)

P0456 says evap emissions. If it went away a day or two later then it was probably the gas cap - wasn't tight enough or turned enough "clicks."

FWIW anytime you have a trouble code you can take it to AutoZone (prob other chains too) and they will read them with a handheld OBD reader for free. Offer parts or whatever but you are not required to purchase anything.


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## papereater (Sep 16, 2016)

3onthetree said:


> P0456 says evap emissions. If it went away a day or two later then it was probably the gas cap - wasn't tight enough or turned enough "clicks."
> .


So, tree, is it still normal for engine icon to show even if there are no codes to retrieve? I did check gas cap, it was tight.


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## HotRodx10 (Aug 24, 2017)

All of the big automotive chain stores will read codes for you. Well, now Autozone hands you the code reader and sends you out to plug it in; it reads and stores the codes, and you return it to them. They plug it in, and the computer provides a printout of the codes and the likely causes.


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## ukrkoz (Dec 31, 2010)

PE, why are you doing htis goofy s... with turning key on and off, instead of using a code reader? It's 2013 vehicle, you know. Who knows, if it even is supposed to have codes shown that way. Just go to any parts store, they'll scan it for you.


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## raylo32 (Nov 25, 2006)

Or go to Wal Mart and buy a perfectly good basic code reader tor $25.



ukrkoz said:


> PE, why are you doing htis goofy s... with turning key on and off, instead of using a code reader? It's 2013 vehicle, you know. Who knows, if it even is supposed to have codes shown that way. Just go to any parts store, they'll scan it for you.


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## Fix'n it (Mar 12, 2012)

many of those code reads will not check abs codes.


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## huesmann (Aug 18, 2011)

But the OP doesn't have an ABS code.


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## raylo32 (Nov 25, 2006)

Exactly. And how often do you get an ABS code? Not very. If you are really budget conscious a simple $25 scanner will work 95% of the time and save you from screwing around at Advance Auto or Pep Boys to get a scan. Or you can really splurge for the $75-$100 one that has ABS.




huesmann said:


> But the OP doesn't have an ABS code.


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## DexterII (Jul 14, 2010)

I agree with preferring an actual scanner, whether borrowing one at the auto parts store or buying one, over the vehicle based one. In my experience, an actual scanner is more specific, and more apt to indicate a current problem versus a past problem. And given the number of repairs you have done, I would really recommend buying one if the budget justifies it. Back to your original post though, yes, if the code went away and the light remained on, I would try disconnecting the battery for a few minutes and see if it resets the light. Having had that exact problem on at least two vehicles, I also agree with 3onthetree that it could very well be the gas cap. I had one that the doggone cap would start a little crooked once in a while and throw a code, so finally ended up replacing the cap, and another, one of my company trucks, that when it said tighten the cap to the first click that's what it meant because going any farther would send a code almost every time. If it's not the cap, could also be something in the evap system, and that's where having a scanner can help nail it down closer.


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## 3onthetree (Dec 7, 2018)

papereater said:


> So, tree, is it still normal for engine icon to show even if there are no codes to retrieve?


Not an expert on OBDII, but DTC's will be active ("Stored" code) if it exists for 2 or more drive cycles and the Check Engine Light is directly associated with having a DTC. Only if it has detected 1 drive cycle failure will it list a "Pending" code and the idiot light does not appear yet. So if you have a light, you have a code, but you can have a code without the light.

If the problem goes away on its own after running through future drive cycles, then the idiot light and corresponding "Stored" DTC will disappear. That is a common occurence with untight gas caps, as it unknowingly gets fixed during the next gas fillup. A more complicated emission failure like vacuum leak or oxygen sensor usually don't go away on their own, they need repaired.

Disconnecting the battery does not clear Stored DTCs, but it may turn off the Check Engine Light until the drive cycle confirms the DTC again. You have to use the OBD scanner to clear a code, but again, it will show back up if the problem has not been fixed.

P.S. I believe, not sure though, for ABS problems OBDII-equipped cars might all have a separate idiot light for that rather than using the Check Engine Light.


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## papereater (Sep 16, 2016)

ukrkoz said:


> PE, why are you doing htis goofy s... with turning key on and off, instead of using a code reader?


Cuz it works, UK. It is a well known method. AND I retrieved the code 1st time around. The mystery is why cant the van allow me to repeat it? 

Yes, I know I can go to AZ- did it many times before. Hate to drive there...LOL.

I will though, if I must. Thanks, UK.


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## papereater (Sep 16, 2016)

I went through all the replies- thanks, people. Until I see an actual problem with a free scan from AZ (in the past they worked out well) I will avoid buying another gadget. I will wait a few driving cycles, then see what happens. I doubt it is a serious driving risk, but will keep an eye out.


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## raylo32 (Nov 25, 2006)

LOL... you will be here again and do this all over... unless you get the gadget and have it when you need it next time. And there WILL be a next time and another next time, etc., etc. That's when most tools are most useful. It would maybe your and our lives a lot easier. ;-)




papereater said:


> I went through all the replies- thanks, people. Until I see an actual problem with a free scan from AZ (in the past they worked out well) I will avoid buying another gadget. I will wait a few driving cycles, then see what happens. I doubt it is a serious driving risk, but will keep an eye out.


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## huesmann (Aug 18, 2011)

As I understand it, the light basically comes on a sensor goes out of range (voltage). Whenever the light comes on, a code is stored. If the sensor then comes back in range, the light goes out. But the code remains stored. So you could theoretically have a number of codes stored, without the light being on. These codes remain until manually cleared.


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## papereater (Sep 16, 2016)

huesmann said:


> As I understand it, the light basically comes on a sensor goes out of range (voltage). Whenever the light comes on, a code is stored. If the sensor then comes back in range, the light goes out. But the code remains stored. So you could theoretically have a number of codes stored, without the light being on. These codes remain until manually cleared.


Thanks, Hue- this may be beyond my expertise, clearing codes. But I am prepared to visit AZ for this soon, then hopefully fix it all up. Will let yous know what happens.


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## raylo32 (Nov 25, 2006)

Car ECMs also store pending codes for faults that haven't reached a set frequency or severity before the light is set. Many scanners will also read these which can be handy if diagnosing an intermittent issue.

And PE, clearing codes is NOT beyond your expertise. With a scanner it is as easy as deleting an e-mail, you just click "erase codes" from the menu and confirm if it asks you. You really should have one as often as you seem to work on cars.



papereater said:


> Thanks, Hue- this may be beyond my expertise, clearing codes. But I am prepared to visit AZ for this soon, then hopefully fix it all up. Will let yous know what happens.


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## papereater (Sep 16, 2016)

raylo32 said:


> Car ECMs also store pending codes for faults that haven't reached a set frequency or severity before the light is set. Many scanners will also read these which can be handy if diagnosing an intermittent issue.
> 
> And PE, clearing codes is NOT beyond your expertise. With a scanner it is as easy as deleting an e-mail, you just click "erase codes" from the menu and confirm if it asks you. You really should have one as often as you seem to work on cars.


Thanks for the kind words, Ray. I might just have to look for one of those. OBD2. But I wont be using it on my 87 Sunbird GT- use a paper clip for that........LOL


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## raylo32 (Nov 25, 2006)

Those were the days... I don't have any OBD1 anymore.



papereater said:


> But I wont be using it on my 87 Sunbird GT- use a paper clip for that........LOL


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## DexterII (Jul 14, 2010)

Hey Papereater, not trying to coax you into something that you don't want or need, but after reading this thread happened to remember something I thought I would share. I used to rely on the onboard displays for trouble codes too but several years back ran into an emission problem on the wife's car that I couldn't track down. Had it scanned at the parts store a couple of times over a couple of weeks, but it was so intermittent that it wouldn't even show up in the history so on the third trip back to the store I finally bought my own scanner, and was able to isolate the problem the next evening. One more trip back to the store for a $10 part, 20 minutes to install it, and it was done. I don't know how long I would have otherwise dinked with it before throwing my hands up, but figured I paid for the scanner on that first job.


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## HotRodx10 (Aug 24, 2017)

If you have a tablet or computer with bluetooth, for about $10 you can get an engine analyzer that will not only show you stored codes, but also real-time readings from sensors, the number of instances of the code occurrence and much more. I bought one a few years ago for $8 and a buddy spent the extra $5 for the upgraded software, and we were able to track down a bad cylinder in my car in just a few minutes. The regular code scanner only told me I had misfire codes for 5 out of the 6 cylinders, but the analyzer told me which one registered a misfire a couple thousands times vs. one or 2 for the other cylinders.


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## papereater (Sep 16, 2016)

Wow- youre not gonna believe this, but I intended to but never had the chance to go to AZ and have them scan my codes, so I disconnected the neg battery cable, and reconnected it. Drove the van and BAM- no more trouble code! Why? I dont know, other than I now have no more trouble code, or check engine light. Maybe it was just a silly loose gas cap(?).


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## Brainbucket (Mar 30, 2015)

papereater said:


> Wow- youre not gonna believe this, but I intended to but never had the chance to go to AZ and have them scan my codes, so I disconnected the neg battery cable, and reconnected it. Drove the van and BAM- no more trouble code! Why? I dont know, other than I now have no more trouble code, or check engine light. Maybe it was just a silly loose gas cap(?).


It takes awhile for the PCM to run the monitors to either pass or fail. Evap usually takes the longest time after clearing codes to run. (Crossing fingers):vs_cool:


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