new egr valve but tranny still wont stay in 4th gear.

[Tim's Buick]

So i replaced the egr valve however, my transmission will not stay in 4th gear. Anytime you turn the car off and restart, it will go into 4th no problem, but after 5 to 10 mins it comes out of 4th and my live data shows 4th gear as being commanded off.

What gives? Very annoying to waste my gas like this... no cel.

[nos4blood70]

I think you need a special scan tool to see trans codes. I'm guessing the EGR valve might be unrelated and it's coincidence. Maybe the 4th gear hub is close to wearing out.

[95se]

Mines odd as well it needs one drive cycle in thr morning. Thr rest of the day itll hit 4th everytime!

[AJT2004]

Mines odd as well it needs one drive cycle in thr morning. Thr rest of the day itll hit 4th everytime!

That is likely normal shifting with a cold engine. Most cars will not shift to overdrive to speed up the time to reach operating temperature, it is suppose to reduce emissions and help gas mileage.

[95se]

I realize most cars do this but i randomly started doing it

[david]

Egr valve has nothing to do with it.And Nos4blood70 is right about the scan tool. Had mine checked and I must have a worn hud shaft. No 4th gear on my car.

[RJolly87]

If it is commanding a downshift, you may want to scan all other live data to see if you can identify an issue. TPS comes to mind, maybe a temperature sensor too

Also, they are correct, it does behave differently when cold, but i believe the magic number is 70*, and it just doesnt lock the TCC

[MattStrike]

Hard parts failure would usually mean no 4th gear ever. For some reason the pcm thinks it needs to stay in 3rd gear if it doesn't command 4th gear.

[95se]

Ok thanks guys, ill start checking sensors and data and see what its doing!

[Tim's Buick]

A good idea.

Heres a funny thing, when I am cruising at 100 kph, the tranny in third, my rpms are at roughly 2800. If I let off the gas to coast down a hill, the tach dips to 1000 rpms and jumps back up immediatly. Wierd...

What should the tps be showing at cruise?

Its funny because when the car is cold, and just starting out, I have fourth gear and tcc lock. But both disappear after 5 to 10 mins. Would the pcm keep the tranny out of 4th because the tcc doesn't lock? I can live without tcc, but no fourth gear kills my gas mileage big time!

[Tim's Buick]

Looking on Identifix, someone stated that 4th gear is inhibited if the TCC does not work. Makes sense as to the way the car has been acting. Makes no sense as to why some engineering brainiac would design a car to waste gas when a simple solonoid goes bad!? At 100, the car is fine at 2000 rpms, but lose 4th gear and it surges to 2500-2800 rpms!!