92' won't downshift

I have a 92' Lumina with a 4 speed automatic tranny. It does not want to downshift automatically and will not go into low gear. If I stop while in OD it will try to take off in OD, same with 3rd and 2nd gears, but even when shifting to low it will only go down as far as 2nd.

About the same time this started the service engine soon light started coming on within 10 minutes or so of driving? Is this some type of vacumn or electrical problem?

also, when I'm on the highway and floor it, it won't hit passing gear either...

Thanks,

George

Need to get that service engine code read and see what's happening.

Make sure you don't have a wiring harness connector from the trans to the ECM pulled apart or something.

The good news is, it sounds like a control problem, not hard parts.

I can't remember if your year had a throttle detent cable from the throttle body to the trans, but if it does, it may have broke or slipped it's adjuster. Take a look.