Wont Shift Into 4th (o/d)

[sc300newbe]

transmission is acting up on my 1992 sc300

just recently i lost 4th gear the tranny just wont shift into 4th (O/D)

some time it will shift into 4th but a few seconds later it will kick back into 3rd

im thinking sensor going bad but i dont know which one

and i dont know what the two sensors on the tail end of the tranny are called. so i cant get diag procedures for them.

[smooth1]

I don't like doing diagnostic work over the boards. To many varibles to account for. So, heres some ideas.

You might be down on hp output. Maybe the issue is in the motor and your only seeing a symptom of the problem. the car is 15 years old. So, what condition is the motor in? Have you had it recently serviced? Ever have a compression check? How is your gas mileage? Have you noticed a slower acceleration or inability to get up to speed quickly?

Are there any cells being thrown up? Most of the driveline sensors are monitored.

Have you checked the fluid level in the tranny? Make sure it's full, but not over full.

Also, how are your engine mounts? If they are bad, over time the motor will start to " rotate" and damage the tranny tines not allowing it to shift properly.

The speed bands in the tranny might be too far out and need to be adjusted. ( $$$) But I usually see this problem in the lower gears not the top.

[sc300newbe]

I don't like doing diagnostic work over the boards. To many varibles to account for. So, heres some ideas.

You might be down on hp output. Maybe the issue is in the motor and your only seeing a symptom of the problem. the car is 15 years old. So, what condition is the motor in? Have you had it recently serviced? Ever have a compression check? How is your gas mileage? Have you noticed a slower acceleration or inability to get up to speed quickly?

Are there any cells being thrown up? Most of the driveline sensors are monitored.

Have you checked the fluid level in the tranny? Make sure it's full, but not over full.

Also, how are your engine mounts? If they are bad, over time the motor will start to " rotate" and damage the tranny tines not allowing it to shift properly.

The speed bands in the tranny might be too far out and need to be adjusted. ( $$$) But I usually see this problem in the lower gears not the top.

yes the motor is in great condition.when i had 4th i got 25mph on the highway. and it pulls hard through all gears.

if any servicing get done it will be done by me. not in any need for service right now. no codes right now. so this is the hardest problem that i have come by. and right about now i am not about to take it to a professional so he can charge me !Removed! ton of money to tell me he cant figure it out and that he thinks i should replace it.

but ne way past couple of days i have noticed when it is cold it will some time shift into 4th but as soon as it gets hot will immediately kick back to 3rd. and also hard acceloration in 3rd up to about 80mph its tries to kick down but will just kick back to third.

[sc300newbe]

bump and now randomly i have 4th only when the weather is cool out

even after a good spirited drive it still is shifting into 4th.

[smooth1]

Sounds like you might not be that far away from needing a tranny rebuild then.

[Kevin Dehning]

I realize this 15 YEARS later but was there ever a solution for this. I have a 1999 doing exactly the same as OP listed.