I have an A4 Avant 2.8L with a DRN transmission code. I did not know that all the transmission were the same, so I replaced with a transmission with FAS code. The transmission work good from first gear up to four then the car goes into limp mode, and will not downshift. The transmission will stay on 4 gear.
Is there a way to fix it or do I need to find a DRN code transmission?
I will appreciate any help.

 

just a thought but check you shifter-is this a tip tronic?-does your cruise quit working at the same time-does the center display quit workin? PRDN5432-if so there is a small magnet located in the under consolethat tells the computer where the shifter is at-it can work loose or misalign- wiggle the shifter gently-does it then go into gear? if you wiggle it to much does it fault out?-had this problem went to a parts store and used scanner to reset it always started to work problem was under the console-hope this helps

 

Yes is tip tronic transmission, and cruise also stop working at the same time.
The code reader says that can not read the input speed sensor.

 

I would go back to the basics - clean all related connectors use dialectric grease - even clean and grease some of the things you are nearby - dialectric grease prevents corrision and moisture build up - reset with the scanner then see what ya get - cleaning and greassing creates a baseline from wich to work - you get a chance to see the wiring-if you need to clean any connectors use some contact cleaner and a toothbrush not a metal one though am not always sure when voltage is present(key on or Off) - keeps me from fryin stuff lol -frayed cracked whatever or hopefully in good shape - if it still throws the code at least you have a place to start - more accurate readings-hope this helps

 

I purchased a new crank sensor, but the results were the same. The car is not able to downshift.

 

You purchased a crank sensor?-thought you said bad input speed sensor?-checked and clean connectors? other sensors can be related to it and not show up-throttle position sensor?-anything related to the trans downshifting- am not familiar yet with all the in's and out's as this is also new car to me but most information transfers from car one to the next-some just ad more junk to it-I accidentally cleared my codes before i could read them so i don't know what they were-but i do know what they were related to(MY SHIFTER ON THE CONSOLE)did you check the harness?- check it again carefully-if it changes when you wiggle it or codes out likely it is the issue-that shifter goes through alot of use over the years- i did download some schematics but have not had chance to look at them yet-will let you know if i find anything and have a code sheet as well-till then

 

Ok here goes-your gonna love this, told you about the extra goodies
1check supply voltage of trans cntrl module
2-kickdown switch
3-multifuntion trans switch!!!!!! in the console
4-ground connections
5-voltage supply of trans solenoids-7of them including shift lock solenoid
6-trans vehicle speed sensor
7-trans input sensor
8-trans fluid sensor-reading correct temp?
9-wiring connection to-
throttle valve signal!!
consumption signal-what you are getting mpg-estimated
engine speed signal
engine intervention signal-low oil pressure-coolant-ignition etc. - i believe
up/down shift signal
Like I said get the goodies you get the crap to-our local library has excellent manuals for my A-4 All Data i think-not chiltons or haynes have checked the local parts houses as well, you can buy a 1yr subscription for your particular car, downloadable schematics i do believe. Get a meter and get into it because there is more to it than i have listed here. Try not to throw parts at it,just gets more frustrating I am still using a meter that i bought from Harbor freight for less that 5 - 7bucks and it does everything i need, paid for itself hundreds of times over in the last 4-5 years
Again-clean it-grease it-test it-and everthing related to it-check for good battery voltage as well, weak cells can wreak havoc on these cars and it is sometimes nothing more than a low battery-Hope this helps-ttyl

 

If I'm talkin out my exhuast pipe someone let me know-any other adivice for this is welcome-Later

 

Let me ask you. The transmission codes is important or not. Like I said the transmission that installed now is different from the orinal transmission code?

 

It is likely important - your transmission computer is likely coded for a specific transmission.