Checksum validation failure? Whats that?

[nicstang]

2005 Chevy SSR, and it tells me "Checksum validation failure" Please try to read VCM again. Ive tried 4 times, with the same results. Any ideas what this means? Thanks

[Bill@HPTuners]

Means the pcm was likely previously tuned and the checksums corrupted, tech 2 to stock should fix.

[nicstang]

This has never been tuned before. Whats tech 2 to stock?

[Bill@HPTuners]

This has never been tuned before. Whats tech 2 to stock?

If thats the line they are telling you either they are lying or it was tuned before they took ownership and just didn't know the history but if theres a checksum issue theres a checksum issue which means it was previously toyed with either in hex or with tuning software such as SCT or diablosport which I believe both just disable the checksums on GM applications rather than calculating them. Maybe they(or the previous owner) had a diablosport handheld and just didn't tell them

Would'nt be the first time the original owner didn't give the whole truth to the person buying the car...

[nicstang]

The owner bought it new, and swears it has never been touched. I was told by SCT that he's seen cheap scanners do this.
Anyhoo, I sent him to the dealership to get a reflash, then come back. thanks for your help.

[Bill@HPTuners]

I don't think a scanner can do this, pretty sure the only way the checksums can be screwed up is via flashing with a file that has the checksums disabled, etc.

[stixandstrings]

So, found out that the Chevy dealer had to reflash the ECM on his truck before he could take it with 6 miles on the odometer! They must have done something to it then. ANyway, I had GM do a reflash and its all good. The only problem is, the speedometer wont change, no matter what I use as a tire size and final ratio. He went from 3.73s to 4.56, and the rate of inaccuracy stays the same. I even stuck in a wildly large tire diameter with no luck. Anyone heard of this?