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attached device may be preventing your vehicle's diagnostic test


I have been receiving from on-star  "an attached device may be preventing your vehicle's diagnostic test from completing.  Unplug any devices from the diagnostic port and try again later."


Car  was taken in for service and found everything was fine.  I then take the car out after two weeks and we are receiving the same issue.  I am sure there isn't anything attached to the diagnostic port because this is the same message after we took it in and had the diagnostic test done.  We only have 500 miles on the car.  





We recommend first uninstalling/reinstalling your app as it is a quick troubleshooting step. If that does not remove the error message, pushing your blue OnStar button will connect you with the Technical Teams who are the most knowledgeable and helpful for issues like this. There may be internal errors that only they will be able to resolve. Be sure to mention that you have already taken your car to your dealer for this issue because they may also recommend that.

New Contributor

Was this ever fixed?  Purchased a 23 Malibu and immediately had this diag from OnStar.  Dealer has tried everything and communicated with OnStar.  Last resort is to replace the OnStar module but delivery for it is sometime in February.  We purchased the vehicle on 12/13 and took it back on 12/16.  Dealer has had it ever since.


New Contributor

I also just purchased a 2023 Malibu and have the exact same problem. started the first day we got the car.

New Contributor

TravisP23 have you found any resolution to your issue?  We are still waiting.  Unbelievable.

We're sorry to hear about this ongoing error you're experiencing. Our team would like the opportunity to look into things further on our end and see how we may assist. To get started, please send us an email with these details to with "ATTN: OnStar Community/dbwhitsitt" in the subject line. We'll keep an eye out for your message.