Q: Why does my 2007 GMC Sierra Classic shifts from 1st gear to overdrive?

asked by on April 25, 2017

Truck will shift from 1st to overdrive, what's the cause?

My car has 158890 miles.
My car has an automatic transmission.

Hello. Most of the time this is caused by a pressure issue within the transmission. It can also occur of there is a major internal failure as that is what the computer does to try and protect the transmission. I would scan the computer for any codes first. Any codes would tell me what the computer may see as a problem. If there are not any codes then I would check the pressures out in the transmission. If you want to have this properly diagnosed then you should take the vehicle to a transmission specialist.

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