I've noticed that at times my transmission will not shift from first to second and my speedometer does not work. I'm not a certified mechanic, but i do believe this is due to the speed sensor. In most cases i can get my engine up to around 4,000 RPM and then everything will kick in and my tranny will shift out of first. A Speed Sensor costs maybe 25 dollars so fixing it shouldn't be a problem for the common person. I Can do it, I just don't have the time, and this problems only occurs maybe once every two weeks.

This is with an automatic transmission. I'd been driving the car all day, it worked just fine. Stopped at a light. Attempted to drive off, car would not exceed 25 mph, then suddenly would not hold any speed. I pulled over, placed gearshift in park. Then checked to see if other gears work (reverse and first would engage). They worked. Placed gearshift into drive again, car did move forward, but would not change into next gear. I let off the accelerator a little bit, 2nd gear suddenly engaged. Still don't know why transmission temporarily malfunctioned.