Check engine light

[mooredata]

Today on the way home from work my car had a check engine light come on. So I hit the Blue OnStar button to have them run a Car diagnostic on it. They did not find any issue after running their diagnostics, is this normal? I've had this happen many times before, but it was always a gas cap issue. The most recent mod I've done was a catch can install this past weekend. Should I have someone like Auto Zone run a scan on it? I would like to avoid the dealer if possible.

Thanks

[Seattle09GT]

Today on the way home from work my car had a check engine light come on. So I hit the Blue OnStar button to have them run a Car diagnostic on it. They did not find any issue after running their diagnostics, is this normal? I've had this happen many times before, but it was always a gas cap issue. The most recent mod I've done was a catch can install this past weekend. Should I have someone like Auto Zone run a scan on it? I would like to avoid the dealer if possible.

Thanks

Yup - go to a parts store, have them run a scan, almost any of them will do it. Write down the code(s) or get a print out and report back on what you find.

[wreckwriter]

Yup, get us the code and we'll help you fix it.

[mooredata]

Is it normal for them "OnStar" not to see any issues? Do all codes show up on the ECM bus. Does OnStar see this Bus traffic? I'm thinking not. I'll have it check on the way home tomorrow and post my findings.

Thanks Seattle09GT

[Seattle09GT]

Is it normal for them "OnStar" not to see any issues? Do all codes show up on the ECM bus. Does OnStar see this Bus traffic? I'm thinking not. I'll have it check on the way home tomorrow and post my findings.

Thanks Seattle09GT

I don't know how deep the OnStar diagnostics go. I always ass-u-me(d) that if the check engine light was on, OnStar could tell me what it is. I bought my own scan tool about six months ago, they are so inexpensive (a basic OBD II reader) that can scan, reset, and save codes. I think I paid $60 for mine and have gotten a few uses out of it.

[mooredata]

When I got my last email report a few weeks ago from OnStar it stated that it could not finish it's Diag, because I may have installed an aftermarket device into my data port, which I did not but I did have a low fuel light on, so I thought that maybe it was this code blocking their scan from finishing. Once I filled up the tank the low fuel message went away I then pushed the OnStar button again to have them run the scan again and no issues were found. Crazy stuff..

[mooredata]

I don't know how deep the OnStar diagnostics go. I always ass-u-me(d) that if the check engine light was on, OnStar could tell me what it is. I bought my own scan tool about six months ago, they are so inexpensive (a basic OBD II reader) that can scan, reset, and save codes. I think I paid $60 for mine and have gotten a few uses out of it. OK, That is Cool where did you get your OBD II reader. $60 is a great price for this tool, the convenience of having this on the fly would be GREAT!

[2StepsAhead]

Theyre all over Amazon, I have one called the AutoXray Code Scout 700 which I use mainly for my Evo (I had some tests bypassed so the cel wouldnt trip...but I didnt know when the IM checks were ready). This has the ability to read, clear and check the IM readiness of the car so you know everything thats going on and its cheap.

[mooredata]

Ok this morning started up the car and no check engine light...wtf....would the code still be listed if I hooked up a reader?

[dandragonrage]

Ok this morning started up the car and no check engine light...wtf....would the code still be listed if I hooked up a reader?

Likely yes. A lot of times you can pull codes without a CEL being on, and the ECU will keep a recent code history.

[Seattle09GT]

Ok this morning started up the car and no check engine light...wtf....would the code still be listed if I hooked up a reader?

Code will be stored in history most likely and then could be cleared out of the history. Undestand how the OBD II system works.

Car throws a code on some system - the OBD II is now scanning so much more than just engine/emissions functions these days. Certain codes will result in a check engine light immediately, others need certain conditions (like a heated O2 sensor is given 30 seconds to start reporting data normally, as it needs time to heat up).

Lets use that heated O2 sensor as an example. Lets say it took 32 seconds for it to heat up, instead of 30, well at 30 seconds it isn't reporting data, or reporting data out of spec, you now have a check engine light.

So you drive a bit. And in driving you shut the car on and off and go about your day, wondering what the heck that light is. But with each time you shut the car down and start it up, the heated O2 sensor is warming up in the prescribed 30 second interval. After several "normal" operations the check engine light goes off. Sorry buddy, I thought the heated O2 sensor was bad but now its functioning normally again, so I turned the light off - don't worry about it.

The A number one reason a check engine light comes on, not just on the G8 but on every car on the planet with an OBD II system is a loose fuel cap.

The number two reason is a failed O2 sensor or mis-reporting O2 sensor.

The number three reason is a false positive. Something burped up on itself, tripped the light, and then started reporting normally again.

Beyond number three you start getting very vehicle dependent on what it means. For example on a Nissan Altima with a CVT, a check engine light reason number four is a bad 1-2 solenoid in the tranny. For another car it could be a totally different reason.

Anyway, that's why a check engine light can be on, then go off, and then come back on again later on.

To answer your other question on where can you buy a scan tool for the $60 range, Amazon, eBay, almost any auto parts store, Costco has a VERY nice one for about $69 which would be a $100 tool almost anywhere else. Unless you're doing your own work on multiple cars, the average home user only needs something that will read codes, store codes, evaluate emissions (if that kind of testing is a concern/requirement where you live), and give you the ability to reset codes. They make some very advanced tools, some of them used at dealers can cost thousands of dollars. You don't need that.

[mooredata]

Code will be stored in history most likely and then could be cleared out of the history. Undestand how the OBD II system works.

Car throws a code on some system - the OBD II is now scanning so much more than just engine/emissions functions these days. Certain codes will result in a check engine light immediately, others need certain conditions (like a heated O2 sensor is given 30 seconds to start reporting data normally, as it needs time to heat up).

Lets use that heated O2 sensor as an example. Lets say it took 32 seconds for it to heat up, instead of 30, well at 30 seconds it isn't reporting data, or reporting data out of spec, you now have a check engine light.

So you drive a bit. And in driving you shut the car on and off and go about your day, wondering what the heck that light is. But with each time you shut the car down and start it up, the heated O2 sensor is warming up in the prescribed 30 second interval. After several "normal" operations the check engine light goes off. Sorry buddy, I thought the heated O2 sensor was bad but now its functioning normally again, so I turned the light off - don't worry about it.

The A number one reason a check engine light comes on, not just on the G8 but on every car on the planet with an OBD II system is a loose fuel cap.

The number two reason is a failed O2 sensor or mis-reporting O2 sensor.

The number three reason is a false positive. Something burped up on itself, tripped the light, and then started reporting normally again.

Beyond number three you start getting very vehicle dependent on what it means. For example on a Nissan Altima with a CVT, a check engine light reason number four is a bad 1-2 solenoid in the tranny. For another car it could be a totally different reason.

Anyway, that's why a check engine light can be on, then go off, and then come back on again later on.

To answer your other question on where can you buy a scan tool for the $60 range, Amazon, eBay, almost any auto parts store, Costco has a VERY nice one for about $69 which would be a $100 tool almost anywhere else. Unless you're doing your own work on multiple cars, the average home user only needs something that will read codes, store codes, evaluate emissions (if that kind of testing is a concern/requirement where you live), and give you the ability to reset codes. They make some very advanced tools, some of them used at dealers can cost thousands of dollars. You don't need that. Great write up. thanks. I did get the check engine light again and here is the DTC code 17:13:29,3 , DTC RAW , 1, 0, 19, 1, 4, 85
17:13:29,3
DTC # = P0455
I'm guess but is that a Gas cap issue. Also, thanks for the OBD II recommendations.

[DRCUSTOMPARTS]

PO455 could be caused by any of the following conditions:

Inspect for a loose, missing, damaged, or incorrect fuel fill cap.
Inspect for a damaged fuel filler neck seal surface.
A blockage or restriction in the EVAP purge solenoid valve, purge pipe, EVAP canister, or vapor pipe, can cause this DTC to set.

[wreckwriter]

Its the gas cap. Make sure its on tight, bunch of clicks. Can your auto store clear codes? If not it will take a few on/off cycles after the issue is corrected to clear, maybe 10 or so?

[HVYCHVY]

PO455 could be caused by any of the following conditions:

Inspect for a loose, missing, damaged, or incorrect fuel fill cap.
Inspect for a damaged fuel filler neck seal surface.
A blockage or restriction in the EVAP purge solenoid valve, purge pipe, EVAP canister, or vapor pipe, can cause this DTC to set.

I recently installed a catch can and occassional will get the PO455 code using the Cortex tuner...nothing shows on vehicle diagnostic shortcut. I clear the code, then it reappears intermently. Is the Evap Emission part of the PCV equipment? I've pulled all the hoses back off made sure the ends were cut straight, no leaks (?) drips or errors, and everything was tight.