Hello. I have a 2001 Sable that does not shift into overdrive. Have higher than normal rpms at highway speeds. Found the transmission breather vent. It is clean. Replaced the dipstick. Has a better seal. Have had some fluid back up before when backing up. I did replace the fluid once. Sucked it out the fill tube. Added some Lucus fluid when refilled. Thought I just had slippage. Now know it is no overdrive working. Any suggestions or thoughts will be appreaciated. Thanks. It is on a Duratec 24 DOHV motor. It has tthe AX4N transmission.
Again, thanks!

 

You don't state how many miles might be on this trans and if it is the original trans.
Something to consider;
If you plan to keep the vehicle for a while and want to depend on it, you might consider replacing the trans with a "Remanufactured" trans.
A reman is better than a rebuilt in all respects except cost. The slight addl cost is worth the peace of mind. There are no shortcuts for solving the apparent problem and of course a lot depends on $$ available, and how long you expect to keep the vehicle. Only you know what you have and how long you want it to last.

 

Thank you for that. The trans is original. Mileage is about 185,000. Got it in 04 with 77k. Motor runs smooth. Taxes are low. Body starting to show some rust. Plan to eventually replace with something newer. Over the last couple of years, I have replaced the fuel pump, rear struts, inner/outer tie rods and tires. Plus a few other things. Plugs , wires, stc.
Right now, just looking for a way to get better mileage. I suspect something like a transmission speed sensor. This site has helped me before. Just looking for some ideas.