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will URS6 ECU work in my URS4 Automatic?

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  • will URS6 ECU work in my URS4 Automatic?

    ECU is 4A0 907 551 B

    URS6 ECU is 551 D or F

  • #2
    Our C4 UrS-cars have an AAN engine that is controlled by a Bosch Motronic ECU (computer). This AAN Motronic ECU has had a number of part numbers, depending on the location and year. Here is a list compiled by Dmitri ("prj") on the S2Forum (who has cracked most of the Motronic codes):

    "AAN Motronic ECU Part Numbers:
    551A early UrS4 with pseudo dizzy and 8k boost chip
    551AA UrS4 non-immo, Europe and America
    551B UrS4 same as 551AA, but auto
    551C UrS6 incorporates all software updates from RS2, different codebase, more diagnostics
    551D UrS6 same as 551C but auto (see photos at the end of this post)
    551E UrS6 has a small tweak to fuel on cold start
    551F UrS6 same as 551E but auto.

    At 551C, when the immo got incorporated, the RS2 codebase was merged as well. Yes, all are still 230hp DIN, 227 hp SAE), but many routines are rewritten. For example the rev limiter routine is different, the software code area in the boost/knock control unit is 200 bytes longer and so on."


    Do the math. You need an auto AAN ecu to work with your auto trans TCU (Transmission control unit)
    RS2'd 93 UrS4 5 spd sedan
    94 UrS4 V8 6 spd manual avant

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    • #3
      so what you saying, it don't work?

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      • #4
        Originally posted by vag_noob View Post
        so what you saying, it don't work?
        Yep

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        • #5
          you kidding? ah come on...

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          • #6
            **** it all I need is spark fuel and air, I'll get this bitch going again

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            • #7
              A ECU from a manual car will work in your car ( as in it will run) I've swapped a tuned manual ECU into my auto and it runs and drives but maybe not correctly

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              • #8
                If you exclude the A version which has a different boost chip, I believe that all the ecu's are interchangable providing the relevant software is used for the vehicle, manual/auto/unimmo/immo. Thats why different pins are assigned for particular functions.
                So unless you have a socketed ecu and the correct sw for your purpose then its a bit of a minefield.
                As other have said you can use manual/auto equivelents (unimmo AA/B/immo C/D/E/F) but the sw is different so they do not perform the same. For example I beleive the auto ecu has a lower rev limit and some tricks for gearchanges.
                You cannot use an immo ecu on a non immo car and I suspect the same is true if you attempt to use immo sw in an unimmo ecu. The car will fire briefly and then cut out. There may be ways round this. One way is to remove the line of code in the sw but then you would also need a chip programmer as well as a socketed ecu! Or you can substitute the unimmo sw. There may be hardware mods but these are not spoken about for obvious reasons!
                I know you destroyed your original set of chips, which in hindsight was not the best idea, as you cannot re-establish the original set up. Do you know with confidence what sw you have and whether its compatable with the vehicle, the biggest issue being if they were for unimmo or immo.

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                • #9
                  Originally posted by vag_noob View Post
                  so what you saying, it don't work?
                  NO. All I am saying is an autobox UrS needs an Autobox-prepped Engine Control Unit (ECU).

                  551B UrS4 same as 551AA, but auto
                  551D UrS6 same as 551C but auto
                  551F UrS6 same as 551E but auto.

                  Autobox ECUs are different because several of the ECU pins (42, 51 and 54 (and maybe 43) are connected to autobox-related portions of the ECU.

                  42/55 - (brown/green)- Gear selection input,e.g. P or N, - Automatic only - if an Automatic ECU is used in a manual trans application this wire needs to be grounded out to gives a 0 in the 4th position in VAG-com measuring block 005. It's default without being grounded is 1 = no start. (Thanks to "MG" on the S2forum for this info)

                  43/55 -Might be Autotrans related (??), not used for manual trans AANs

                  51/55- Not used for standard transmission cars - relates to kick-down shift point for automatic trans cars. Third digit in VAG-com measuring block 005. Normally "0" until kick-down with Autotrans when it goes to "1". (Thanks to "MG" on the S2 forum for this info)

                  54/55- Not used for standard transmission cars - relates to automatic trans cars

                  REFERENCE: AAN ECU Pin-out Post:

                  http://forums.quattroworld.com/s4s6/msgs/21009.phtml

                  RS2'd 93 UrS4 5 spd sedan
                  94 UrS4 V8 6 spd manual avant

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                  • #10
                    Originally posted by twoqu View Post
                    I know you destroyed your original set of chips, which in hindsight was not the best idea, as you cannot re-establish the original set up. Do you know with confidence what sw you have and whether its compatable with the vehicle, the biggest issue being if they were for unimmo or immo.
                    Yeah I did a 30 minute round trip in the car with new ECU chips installed before I cleaned the board.

                    I software is PRJ don't know which version, ran flawlessly.

                    Can I just swap chips into D or F, will that disable immo? From what I read, yes?

                    I have soldered new headers onto the stock chips, got the same result as new chips.

                    Trying to source ECU before girlfriend gets sick of taking the train to work. Then a new hobby.. fix old ECU.. possibly a hopeless enterprise.
                    Last edited by vag_noob; 18 April 2017, 06:32.

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                    • #11
                      As I said previously, any version of the ecu would work (except A) providing it is socketed to take the sw you have. The p/n of the ecu reflects the different sw really. That should help widen the market for replacement.
                      Of course the correct replacement would be as Dave said the 551B if you are concerned about originality.
                      As the sw is ok its just a matter of finding an ecu. The ID of the ecu is in the sw so if for arguments sake you but 551B sw in an 551F ecu it would ID as a 551B in VCDS/Vagcom.

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                      • #12
                        Originally posted by twoqu View Post
                        any version of the ecu would work (except A) providing it is socketed to take the sw you have.
                        "Any version"? DO NOT think so. Because of his automatic transmission, he needs an Autobox-prepped Engine Control Unit (ECU):

                        551B UrS4 same as 551AA, but auto
                        551D UrS6 same as 551C but auto
                        551F UrS6 same as 551E but auto

                        RS2'd 93 UrS4 5 spd sedan
                        94 UrS4 V8 6 spd manual avant

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                        • #13
                          Acquired a 551D unit, installed chips, we have ignition Will test drive tomorrow.

                          *update (late), works perfectly
                          Last edited by vag_noob; 19 May 2017, 08:09.

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                          • #14
                            Three years later, still works perfectly.

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