HummerGirl,

That just happened to me a week ago. The check engine light came on, it lost overdrive and it was stuck in third at any speed. I called Onstar and they said to take it to the dealer within seven days. I Towed it to the dealer and they fixed it within the hour. They had to replace the electronic key assembly; it’s the mod behind the key in the steering column. It stopped sending 12v to the transmission computer. It was a quick fix, It happens! BIG-C

White 03-H2-LUX

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