Iv done quite a bit of research on trans issues. However nothing as peculiar as what happened the other day. I have a 1997 blazer LS 4x4 automatic trans. Intermittent hard shift from 1st to 2nd. Getting onto freeway and accelerated fast to about 60 and then it down shift on its own to first or second. Causing my motor to rooaar! I pulled over put it in park, then back to Drive and shifted fine again. As soon as I accelerated hard again it wouldnt shift out of first. While driving put it in N, back to D...no difference until I stopped put it in park, back to D and nursed it home.

Went to get my trouble code/s read. Coudlnt because a fuse was blown.(Fuse 7 Pwr Aux) Fixed fuse (AUtozone closed by then) and havnt had any issues since. Got my codes read and it was the TPS sensor low voltage circuit. Hasnt done anything as peculiar.

What in the world could be on the Pwr Auxiliary circuit that would cause such crazy confusion with the PCM? Thanks in advance fellas.

 

I'm assuming that is 60kph (~40mph) since that is typically when 1st gear tops out.

I would test the TPS sensor by measuring the output from sensor making sure that it ranges from ~0.5V at closed throttle up to ~4.5V at wide open throttle. Maybe read the code sheet --> P0122 - Throttle Position Sensor Circuit Low Voltage