Where exactly is the Transmission Vacuum Modulator

located on a 1998 Lumina 3.1?

Maybe someone got a picture of the location?

And is it very difficult to change it?

Thank you

Some words from Haynes manual.

"has an important effect on shift quality. If your vehicle exhibits shifting problems such as slipping or harsh shifts that are either too soft or too harsh check the vacuum supply to the modulator". Says vacuum should measure 13-17 at the modulator idling hot in drive brakes applied.

The pictures in my book are zoomed in very close so not obvious but studying my car and features in the picture it appears to be on the front of the transmission looking down between the drivers side dog bone and the air cleaner.

It looks like one of the easiest things to change on this car. Disconnect the vacuum line and then there's an obvious mounting bolt and nut and you use a magnet tool to remove the valve. You need a new oring for installation.

Thank you. Will try it.

Check the fluid level before diving into the modulator. The code is indicating slipping which could be exactly what is happening.

I checked the fluid level this morning before I started the car.

The level is a little bit over the second hole on the dipstick, means a little bit over max.
Does this cause the problem?

Did you check the level at normal temperature? If so it doesn't sound to be too far from normal level although the manual emphasizes it should be between the holes. Suppose if it were way overfilled you could get foam and slipping. The fact that this started after you changed the fluid seems to blame that process as appose to a fault with the modulator. I guess I'd recheck the level and get it between the holes then clear the code and see what happens before changing the modulator. If the modulator is not very expensive and appears to be the original maybe it would be worth yanking just for added confidence in the car. The book says a bad diaphragm in the modulator can cause smoke out the tail as tranny fluid is pulled into the engine and burned. You could also verify correct vacuum at the modulator.

Hm just read you post again and you said you checked it before starting the car so cold? Proper check is operating temperature. Parking brake on engine running and sweep the gear shift through all gears and end it in park then read the stick. It could be significantly above the hole at temperature as oil expands.

Do you mean with normal temperature I have to drive it till the engine is warm or just run the engine in park and wait till it is warm?

Here on the pic you can see were the fluid is.
A GM mechanic changed the fluid and filter.

http://img190.imageshack.us/img190/8572/c6az7a020c.jpg

My 98 3.1L owners manual says to let it run at idle for 3-5 minutes and keep the engine running while checking it. I pulled my stick and it has ADD 1PT/.5L and then the crosshatched pattern with a small reference hole at each end of the hatch pattern above it which agrees with the manual. The manuals say the level must be within the crosshatched pattern. Is the picture you posted of a 98 Lumina stick or just something you found for discussion because it's either short or those are two rivets attaching a longer piece to the handle but the handle doesn't look like mine?

I don't have a owners manual anymore. Don't know where I lost it.
The dipstick is just an example from the internet. The fluid is in cold over the second hole. So I think there is way to much fluid in. I will do the procedure you wrote tomorrow, since it is already dark here and let you know.

Thank you and Happy New Year.

fyi i think the part you are looking for is in this pic .. look for the small bit of blue shop towel in lower right side of pic, I have the paper towel stuffed in the vacuum inlet to keep dirt out while i was working on it... dont have better pic of it. right side of exhaust manifold

http://www.automotiveforums.com/vbulletin/attachment.php?attachmentid=38711&d=1269811714

Got it thank you very much.