So many innocuous things can trigger a CEL -- different EVSE, voltage fluctuation on the line -- that a CEL which cycles off and disappears a day or two later is likely not worth worrying out. My suggestion is to see if you get another and if there is any pattern.
I believe onstar only reads what you yourself could grab with a standard OBD reader.
There are other subsystems that have their own codes that a dealer can read.
These generally throw a code in the main system, though. e.g. P1E00 is powertrain requested MIL illumination (or similar wording)
But as said, it's probably a code that the computer recognized had corrected itself and turned off the light.
It may still be in history in the ECU, though.
I do not think it is a waste to be an informed owner. Why wait until you get to the dealer to find outs what is wrong. Having OnStar read the trouble codes is a benefit. I agree that having them make an app't is not worth the time.
I had my CEL come on two weeks ago with P0CD2 and P1E00, (Charging and LI-On battery issues). By the time I could get an App't and get the car in, the light went out. The service rep said if they can't find anything that they would charge me $125. Since the car was driving and charging with no issue I declined. Well, the light came on again today with the same codes. I now have a history for my records. This Tuesday I will leave the car and have them check it out.
So if I did not have OnStar read the codes and IF the dealer did not find anything then I would be a frustrated owner. I know the car keeps a history in the computer. I also know that the codes gets cleared out after a certain number of car starts.
Hello Thanks for the feedback.
The dealer can charge $125 for a code that dissapears, even if under warranty? That is incredible. That can not be standard policy at all dealers? I hope.
If the code is not active but in the history it may eventually go away. So we still can lose any record.
I had made a appt but canceled it when the light and code went away. For those that have the time it is probally better to go to the dealer and have the issue logged in. It hard to tell for sure how big a deal something is. When I had the 2013 Volt lease I sometimes had to turn the car off and on to start it or get the drive to work. Now that this 2015 Volt is my car I am being a bit more cautious when these things happen. Especially if they happen close to the bumper to bumper warranty. But I only have 17000 miles, so should not be a big deal right now.
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