AT problems. 2004 Dodge Neon?

Question

Yesterday i was driving my car, a Neon 2004, and the check engine light came on, then the gears of the transmission will not change anymore.
I think it got stuck in 1st or 2nd gear.
The R, N and P gears still work fine.
I used universal type ATF, "Chrysler" compatible.
I overfilled it pass the "hot" limit in the stick, but just for like half an inch or so, and i leave it like that. I measured the level with the engine hot, running and in park position.

I just need some advice from someone of you, so i have an idea of what to do and believe after hearing the mechanic's diagnostic of it.
Here is a tip that might give a better idea of the problem.
Before this happened, the car moved like half an inch forward while waiting for the stop light, like if you get hit from behind, but not too violent. Just a push... this happened like 3 times before over the month, until this last time yesterday. The same push activated the check engine light and then no more transmission the next second. Thx!

Answer 1

Check engine engine light usually indicates a engine emissions control problem. what you need to do is have someone hook up a code reader and see what default code was set. Just plug into the OBD II outlet ASAP as engine could be in the limp home mode.

Answer 2

Not sure on which years, but the Chrysler A604 transmission was used on the Neons I do believe. They have a "limp home" mode whereby if there's a big problem within the transmission, it will only allow shifts up to 2nd gear. I've read they are VERY sensetive as to what ATF is used also. Either way, have the car scanned at AutoZone or something like that to see what the Check Engine light is on for first. From there, check to see what the transmission is doing. May need a flush and a reprogram of the computer.