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I have searched this forum for prom id posts with no results. I have always been curious about the 'all prom id' prompt when retrieving codes, but scared to try it because a service manager once told me I could mess something up. I figured they wouldn't put a button on the dash that anyone could use to hurt their car, so I tried it today. I know it means programmable read-only memory and each of the 15 systems has a four character id. Well, I get a NOT SUPPORTED BY PCM message for the PCM system. My car runs perfectly and am not getting any codes or MIL's. It's just one of those things that make you wonder if it doesn't hurt anything, then why is it there? Does anyone with a 98-00 STS get the same message for their PCM? Are there any GM engineers(Guru?), techs, or other knowledgeables who could explain why this happens but does not affect the car?

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Not quite sure what your asking about....

Older GM computer diagnostic software used to have a list of what PROMS were available etc to fix whatever problem etc. For example, there was a newer PROM to fix some PO39 code issues.

Depending on the GM vehicle....all of that changed to software version around '94-96.

So the older cars used a chip, newer cars use software.

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