Astina 1989 automatic low & reverse fine but does not change up through gears, oil has been changed with no improvement. How does car tell gears to change, via road speed, vacuum or speedo drive ?? Thanks

 

Col: It's a combination of things: Gear selection sensor, throttle position sensor, vehicle speed sensor and maybe a few other things.
It could also be that a shift solenoid is stuck.
I don't have enough experience with automatics to be of further help. Hopefully someone else jumps in.

 

Hi, thanks for the gen, your thinking seems to be going along with mine, a sensor problem or relay, possibly the hold relay locked up. Thanks again, Colin