I have a Pontiac g6. its not shifting into third and four gear. Is it the transaxle control module?

I'd start with the basics...the fluid level HOT...look at the dipstick and fill up to the hot mark....check the stick to see if the transmission fluid is black or smells burned~ look for leaks if the level is low~

The tranny is controlled by the PCM, it controls the engine also. It's more likely that your tranny is failing. When you check the fluid, check the color.

These do not have a dipstick so you have to stick something clean into the check plug to get a sample to check the color. Here is a pic of the plugs.

It's close the 60/65 are for the larger cars and the 40/45 are for the smaller cars. They probably share part design. There are some differences that I know of.

If the fluid is burnt and/or has alot of clutch pad material Lucus tranny fix may help for awhile. My 4T60e in my Monte has a bad slip in OD. I'll dump in the Lucus untill it goes then swap it out.

It won't shift out goes in drive fine goes fine just don't shift it's set 6 months or longer