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Thread: 2005 gto A4 to T56 U2105

  1. #1
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    2005 gto A4 to T56 U2105

    So, to give you some background, I have a 2002 VU Ute that I swapped a 2005 GTO LS2 and T56 into.

    As if that wasn?t enough bastardization, the GTO engine and trans are not related to the donor harness or BCM which are for an automatic car.

    Now, I bought HP tuners and told the ECU that it was a manual now, but it is still throwing TCM codes. Or it was. I had grounded the neutral safety switch pin on the auto ECU to get it to start initially, but now that it thinks it?s a manual I think that may have been causing me some issues. So, I ungrounded it and it has not complained about the tcu since.

    It IS still throwing code U2105 though. I should also say that I have a traction control button on order but right now there?s nothing plugged in where it should be.

    Do you think U2105 is the ECU complaining that it can?t see the traction control button?

  2. #2
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    U2105 is a GM high speed LAN DTC saying that there is a loss of communication with the ECM across the high speed network.

    What module sets the U2105?

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    I wish I knew. U2105 is the only code triggering my SES annoyer chime so I want to get to the bottom of it.

  4. #4
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    Do you have a DLC and high speed data circuit in the car from the swap?

  5. #5
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    Yes. The entire dash and harness came out of the GTO. Ecm, bcm and pim are all from the GTO. The original GTO was a4 though, and I put a t56 behind it. I toggled the trans type to ?manual? in HPT, but it?s still complaining about the tcm. It just threw that u0101 tcm code again.

  6. #6
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    I DID leave the tcm out when I went t56. I didn?t figure the ecm would even look for it once I toggled the trans to manual in the software?.

  7. #7
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    The drop down menu for automatic to manual does nothing. The base file has to be a manual for it to really be a manual.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Can you plug the TCM back in and see if the DTC goes away? The high speed LAN system is probably missing the TCM CAN messages and its not happy.

  9. #9
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    Quote Originally Posted by 5FDP View Post
    The drop down menu for automatic to manual does nothing. The base file has to be a manual for it to really be a manual.
    That's what I have been reading. But what does it mean? I can get a 6MT calibration file, flash it and be good to go? Or is this a Tech2 dealer flashy thing?

    Quote Originally Posted by cadillactech View Post
    Can you plug the TCM back in and see if the DTC goes away? The high speed LAN system is probably missing the TCM CAN messages and its not happy.
    Unfortunately, the engine harness came with the donor engine/transmission set, so it is set up for the T56 and doesn't have the TCM plug. I DO have the MT ecu that came with the engine, but it wont be paired with my PIM/BCM... Isnt that a nightmare of a process that involved a Tech 2 also?

  10. #10
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    Quote Originally Posted by twoutes View Post
    That's what I have been reading. But what does it mean? I can get a 6MT calibration file, flash it and be good to go? Or is this a Tech2 dealer flashy thing?



    Unfortunately, the engine harness came with the donor engine/transmission set, so it is set up for the T56 and doesn't have the TCM plug. I DO have the MT ecu that came with the engine, but it wont be paired with my PIM/BCM... Isnt that a nightmare of a process that involved a Tech 2 also?
    If the BCM and all the other donor modules are programmed to have a TCM CAN message going through the CAN bus and you removed that, I think this is your problem. Each module monitors the CAN bus for the appropriate messages and if there is something missing then they set DTCs.

    The PIM takes ECM, EBCM and TCM CAN messages and passed them along to the DLC and the BCM. This may be your issue too as the PIM wants to see ECM and TCM messages.

    If you have the DLC and can access the other modules from the swap, see what they are reporting for DTCs.

    The GTO CAN system is unique as this was the era as GM started adding in high speed CAN as well as running 2 more more other protocols at the same time.

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    GTO CAN.jpg

    Here is the schematic in case you didn't have it.

  12. #12
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    Gotcha. I'm going to see if I can get my hands on a Tech 2 and start digging.

    Thanks!

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    It gets even more bizarre...I do have a tech 2 on the way, so I will have more insight into what is causing all of this soon, but I finally got a TRAC button in the mail. I installed it and trac still wont turn on, which is not surprising based on my current codes and issues. However, with the TRAC button plugged in, the ignition wont give me my key back! It prevents full travel to "off" and key release. Pulling the negative cable allows the key to come out. I unplugged the TRAC button and that also allowed the key to come out again. So weird that the TRAC button is tied to the ignition interlock...

  14. #14
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    Quote Originally Posted by twoutes View Post
    It gets even more bizarre...I do have a tech 2 on the way, so I will have more insight into what is causing all of this soon, but I finally got a TRAC button in the mail. I installed it and trac still wont turn on, which is not surprising based on my current codes and issues. However, with the TRAC button plugged in, the ignition wont give me my key back! It prevents full travel to "off" and key release. Pulling the negative cable allows the key to come out. I unplugged the TRAC button and that also allowed the key to come out again. So weird that the TRAC button is tied to the ignition interlock...
    gto can 1.jpg

    Looks like the traction button is a direct input into the PIM.

  15. #15
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    Quote Originally Posted by cadillactech View Post
    gto can 1.jpg

    Looks like the traction button is a direct input into the PIM.
    These cars know way too much... :P I cant wait to get the Tech 2 and gain some insight!