Dodge Repair: 98 Avenger: trans wont shift out of 2nd gear, transmission control module, dodge avenger

Question
hi! i have a 1998 dodge avenger i was driving to work the rpm's flew up but wouldnt switch gears i did 25mph in first gear to work after work got in drove normal same thing happened 1 week later some 1 told me i need a new transmission..but i don't think i do because it works some then doesn't work some someone suggested to me the speed sensor..i have no clue idk if it helps at all but i also have a clogged catolic converter..

Answer
Hi Cody,
It appears that you are in 'limp mode' which happens when the trans senses a problem and wants to avoid unnecessary wear or damage until it is repaired.
Fortunately the transmission control module and the engine (powertrain) control module have a self-diagnostic capability which is communicated by four-digit fault code numbers which you obtain by inserting a code reader into a socket under the dash next to the steering column.
You can often get a free code readout at a nationwide auto parts store such as Autozone or you can go to an independent repair shop and they will do the readout for around $40. Ask for the number(s), what they mean, and what they recommend doing. Then send me a follow-up question telling me the results, we'll compare what you were told to what the shop manual says about the specific codes and go forward from that point.
I would not buy/replace anything until you have the fault codes. A speed sensor (there are two of them) might be the cause (and each has its own fault code) but there are about 40 other codes so you don't want to guess at this.
The catalytic converter is of course unrelated to the transmission problem so deal with that separately.
Please read the PS below.
Thanks,
Roland