Recently I bought a 99 Bonneville for 300 bucks to drive to work and back. I knew this before i bought it, but it doesn't shift into overdrive. Seems to shift fine into all other gears, and has no whining sounds or any other odd behavior. If i manually shift from od to d or d to od rpms do not change.The fluid looks ok and does not smell burnt. Not wanting to really put any money into this, I was just wondering if anyone had any suggestions.I have been reading about a tcc solenoid or stripped out splines on 4th gear, but i would greatly appreciate any other possibilities. If it seems to be an expensive fix, I will probably have some fun with this car in the demo derby this summer. Thanks for any info you may have.

Have you have the car scanned? Some of the transmission codes don't set of a light, but will store a code. Post that code here and we could tell you more. One thing that can prevent the trans from shifting in to 4th is a bad fluid temp sensor. But that'* inside the trans and needs to have the side pan removed to change it.

I did scan the codes cuz the check engine light was on, but I also had to change the intake and egr tube. None of the codes seemed tranny related. one was o2 sensor but cant remember what other ones were, I had cleared them and they haven't came back. i figured they were old ones from the engine flooded with coolant when the intake went. One other one was multiple cyl misfire, which is probably a given. I also don't know if that scanner reads tranny codes or just engine codes? It was one borrowed out from the local O'Reily store. If the check engine light isn't on, will a tranny code still be present?

Ya, several trans codes wont trip a light. The trans codes are P codes so they should still show up on a code reader.

I will run another scan tomorrow and see if anything comes up, and this time i will write them down. There was a P code on there but can't remember what, and thought if it cleared and didn't come back, it was from the intake problem.

Does P1811 ring a bell?

No not really, the guy i bought it from also said they had it hooked up to a scanner at a tranny shop and they tried to shift it manually with that( if thats even possible, I don't know) and they couldn't get it to go. Not too sure about any credibility with him though.

If the splines on the 4th gear input shaft was stripped I would expect it to go in to 4th and slip. SGP358 is the trans guy here. He may have more in site.

Yea I guess that would make sense. I'll scan it tomorrow and let ya know what I come up with. Thanks!!!

This is what I found but it doesn't make sense to me.
P1811
Transmission 4-Wheel Drive Low Indicator Short Circuit To Ground