Check transmission fluid

The automatic transmission fluid fill location on a 2008 BMW 650i can vary depending on the specific model and transmission type, but generally it is located under the hood and accessed through a dipstick tube.

To locate the dipstick tube for the automatic transmission fluid, follow these steps:

1. Open the hood of the vehicle and locate the transmission fluid dipstick. The dipstick handle is usually yellow, red, or black and is labeled with "ATF" or "trans."
2. Remove the dipstick from the tube and wipe it clean with a lint-free cloth or paper towel.
3. Reinsert the dipstick all the way back into the tube and then remove it again. The fluid level on the dipstick should indicate the current level of transmission fluid.
4. If the fluid level is low, you will need to add automatic transmission fluid. To add fluid, remove the dipstick and use a funnel to pour the fluid into the dipstick tube. Be sure to use the correct type of transmission fluid specified in your owner's manual.
5. Check the fluid level again with the dipstick to make sure it is at the correct level. Add more fluid as needed.

Note: It is important to follow the recommended procedure for checking and adding transmission fluid to your BMW 650i to avoid overfilling the system, which can cause damage to the transmission. If you are unsure about the location of the dipstick or how to properly add fluid, consult your owner's manual or a qualified mechanic for assistance.

You have to have a special dipstick tool in order to check the fluid in them transmissions! Here's a link to a sight that may help you, but if you do check the fluid the vehicle must be on a lift in a level position to check the fluid.

But, unless the transmission is leaking fluid? Then it would not be low. Unlike engines, transmissions do not use fluids, they would only leak, IF they had a problem.
https://www.2carpros.com/questions/2008-chrysler-town-country-check-fluid-38l-van

The first thing I'd check is the level of the transmission fluid. Make sure the vehicle is level, and is up to normal operating temperature. Check It while it is running. If it's low, there's your problem. If it's okay, then you may need to change the transmission fluid and filter. The transmission filter is similar to a filter on an A/C unit. Like a screen to catch the junk in the fluid. It's located inside the transmission pan on the bottom of the vehicle. If you do it yourself, make sure you use the right type of transmission fluid. Filters and fluid are relatively inexpensive to replace.
With all of that being said, all of that information was for an automatic transmission. Not for a standard transmission. If your transmission fluid level is okay, and doesn't need changing. Take heart, that doesn't mean you're looking at a complete transmission replacement either.

Have it checked with a scan tool and also check the transmission fluid level and condition.

Open the hood. On the driverside at the radiator. Look down and you see a black cap on the front transmission cover. This is were you check the level. The car needs to be at operating temperature and running in park to check. Unscrew the cap pull it out. Wipe it off and reinstall. pull it out again and check the fluid. Fluid should be in the hash marks. It takes dex VI. synthetic.

Engine must be running to check the fluid level. Transmission should be hot, not cold. Then remove plug. Add transmission fluid until it comes out of plug hole. If the engine is not running and you remove the plug, you will lose a lot of transmission fluid.

Transmission/primary or engine????

Engine drain plug is in a rubber hose that hangs down under the motorcycle transmission area at about the point where the kickstand rests in it up position. It has a worm clamp that you would loosen with a one quarter inch socket to allow you to pull the plastic plug out to let the engine oil drain out. The transmission/primary drain plug is on the bottom of the primary cover right below the middle of the clutch inspection (derby) cover. It is a 5/8 inch hex head plug

1. Switch off the car
2. Pop up the hood and raise it
3. Locate the transmission fluid cap
4. Remove the cap to add fluid
5. Check the owner's manual on what type of fluid your car requires and in what quantity. It is essential to use the right fluid and not anything off the shelf.
6. Remove the dipstick and start filling up the fluid slowly - you don't want to add too little or overfill.
7. Now put back the dipstick, switch on the vehicle and start shifting gears. Remove the dipstick and see the marking to know if you your car has the right amount of fluid
8. Put back the cap by turning it clockwise.

If your 2008 Avenger is set up like the Breeze, Cirrus, Stratus, or Sebring that it evolved from (and I don't see why they would change a successful platform), when you are facing the car the engine is on the left and the transmission is on the right (driver's side). The transmission dipstick should be the one between the engine and the transmission near the center of the engine compartment. When you pull the transmission dipstick, it should say something about the type of fluid required, and under what conditions to check the fluid level (usually on a level surface at normal operating temperature while in park). Add fluid if needed, and be VERY careful not to overfill as newer transmissions are very sensitive to fluid levels. Going as little as a couple of ounces over can adversely affect transmission performance and longevity. By the way, I strongly recommend changing your filter and fluid every 24,000 miles to keep from having to replace the transmission at arround 130,000 miles. The Mitsubishi transmission in my Eagle Vision (same as a Dodge Intrepid) disintegrated at around 137,000 miles and cost me $1380 to replace. Regular maintenance by the prior owner would have saved me that expense.