I have a problem when I start the car it will not go into a gear, but when the engine is not running it goes into al gears. I filled brake fluid and it worked for 1 day and now doing the same

With the van in park or neutral with e-brake on, and engine running, pull the transmission fluid dipstick, notice there's no fluid on the dipstick. Put a quart of transmission fluid in the dipstick tube, with e-brake still on, put the van in gear. R or D, and see does the van try to move against the brake. If it tries to move, engine speed drops, put it back in neutral or park and check the fluid level again. If it's still low, put in a little more till it's to the full mark.. Done. Check under the van and find the area where fluid is dripping out and fix it. If it's the pan gasket, replace it. Replace the filter while the pan is down.

if its the the gear selector is moving and not going into gear ----under hood drivers side under brake mastercylinder is the top of transmission the gear selector cable connection is there check that it hasnt come off,loose or damaged ----=if selector does go into a gear and trans not responding look under drivers side and thru wheel wells for fluid leak ---theirs no dipstick so to check fluid
There is a black cap located on top of the trans almost directly under the brake master cylinder. It's about 2 inches high, 3 inches around. That's where you add the fluid. The checking procedure is as follows: Start the engine and allow the engine to idle until the transmission fluid temperature has reached the value specified. 104 degrees F.
Depress the brake pedal and move the shift lever through the gear ranges, pausing a few seconds in each range. Return the shift lever to the PARK range.
vehicle must be level with the engine running and the shift lever in the PARK range.
Remove the transmission oil level control plug.
The plug in an 11mm bolt located between the r/s axle seal and the oil pan.
Check the fluid level. The fluid level should be even with the bottom of the threaded plug hole.
If you remove the plug and nothing comes out, add about half a quart at a time until the fluid starts to dribble out. Once it stops, the level is good.this is the procedure to check fluid if their is fluid and problem still persists the transmission module and or internal transmission damage possible which a mechanic {transmission}would need to diagnostic check the following link has multi videos for the cobalt transmission 05 Cobalt Transmission Fill Yahoo Video Search Results

You can test the clutch hypothesis. Carefully put the car in gear for a safe direction, then depress the clutch and turn over the engine. If the car lurches, then the clutch is not working. In this case, check the linkage to the clutch, or if yours is hydraulic, check the fluid level in the clutch master cylinder. If the cylinder is low, then don't stop by just filling it, you want to find out where the fluid went. Look for leaks - especially around the clutch slave cylinder.
If on the other hand your engine it starts with the transmission in gear and the clutch down without lurching, then try letting the clutch out slowly. With any luck you have it running and in gear. See what happens next. Good Luck!

Eric, how are you confirming whether or not the car goes into gear if you shift gears without the engine running? One way would be to put it in 1st and see if you can push the car. If you can't, it is in gear.

Another option is to roll the car slightly forward or backward (engine off) while trying to put the car in gear. Once it is in gear, then the car shouldn't move any further. However, if it goes into gear, DO NOT start the car without taking it back out of gear.

The clutch is much more likely to be the problem than the transmission.

If the clutch fluid ever ran dry, then the clutch hydraulics will need to be bled of air. Otherwise, the problem could be the clutch master cylinder, slave cylinder or throwout bearing. Since you didn't report the clutch slipping (e.g. engine revving without accelerating when in gear) it is likely not the clutch disks themselves.

Fluid must be hot ,engine running in park on level surface

is the fluid in the trans over filled and foamy? check the level and color (red not brown) it should be low on the marks when cold and running in park. and high but NEVER past the marks when hot.

Start the car and go for a drive to warm it up.When you are ready to check the tranny oil level,pull the h/brake on and go through all the gears slowly and finish in N.Now check the oil level with the engine still running.If it needs oil,you add it down the tube that the tranny dipstick goes.Tranny oil bottles often come with a tube made into the lid to make things a bit easier.Hope this helps

Start the engine and allow it to get to operating temperature.

Place the gear selector in Reverse, then slowly through all the forward gears, while holding the brake.

Replace the selector in Park, but leave the engine running.

Check the transmission fluid level.

If low, add fluid until level is correct, then repeat above procedure and check fluid level again to ensure that transmission is filled to proper level.

If level is correct, perform fluid/filter exchange. If problem persists, see qualified service technician for further diagnosis. Transmission damage will require overhaul to repair.

Here is the procedure:

The transmission temperature must be between 86° to 130° F (30° to 55° C) before checking With engine running, switch on AC While holding vehicle with brakes, place transmission into each gear briefly With engine running and transmission in park, remove Fill/Check plug. If a small amount of oil runs out, fluid level is correct. If no oil runs out fluid level is low, add fluid as required through Fill/Check plug hole. When level is correct, reinstall Fill/Check plug and tighten to correct torque.

I'm having the exact problem! To get it in gear, turn key to unlock, put in neutral, start then in gear. That's as far as I've gotten with a solution to at least drive it. Next will check the brakes...yeah it sucks! Hope there's better advice commong...