They will make you buy another bcm, from then, and flash it that way.
its like $800. Ask me how I know.

 

Ask your mechanic what the codes are (likely Bxxxc and maybe Uxxxx). We may be able to do a little digging.

This might be the result of an anti theft system falsely engaging due to something like the BCM not receiving a signal from the ignition cylinder. Don't know, speculation. But knowing the codes will help us to maybe sort this out...

 

After taking the vehicle to the local GM dealer it was finally determined that wires had fused somewhere beneath the console causing different elements in the system not to be able to communicate. The damage was repaired and now the car starts as it should. Cost $240

 

Happy to hear you got your car fixed. And that $240 is a LOT cheaper than buying another BCM and having it flashed. Congrats and enjoy your ride.

 

Considering it was probably 125 for diagnosis, 125 for a fix, I'd say you got through that with a minimum of financial damage.

Were there any blown fuses?

Might want to shop around for a new mechanic. Everyone gets things wrong now and then but......
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Enjoy .