Q: Put a new transfer case on, now tranny won't shift out of first unless I do it manually

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I replaced my transfer case bc the old one was busted and leaking transmission fluid. I put the new one on. When I put it in drive, the transmission will not shift out of first. However, I can manually shift from first to second. It won't go past second gear. Reverse works fine as well. The speedometer and odometer are not working, and the ABS light and parking brake light stay lit. My transmission was fine before I changed the transfer case. I believe it is electrical. Please help!

My car has 250000 miles.
My car has an automatic transmission.

Hi there, thanks for writing in about your 2000 GMC Sierra 1500. Your transmission and ABS system need a vehicle speed reference to operate correctly. The transfer case has two speed sensors located at the rear extension housing. Inspect the wiring to the sensors. If it looks good and is undamaged, you could try removing the sensors from original transfer case and installing them in the replacement. The transfer case speed sensors put out an A/C voltage when the driveshaft is rotating. If there is no voltage, something internal is wrong with the transfer case. To have this issue addressed, I recommend having a qualified professional, such as one from YourMechanic diagnose the shifting issue in order to have this corrected.

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