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Thread: T42 tcm

  1. #1
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    T42 tcm

    Pretty sure i need a new TCM, 2005 Corvette A4. Car randomly started wondering looking for gears slamming in and out of gear. Didnt get any codes replaced the VSS, still happening and now it gets worse. Replaced the VSS last night, drove it to work this morning and drove great not a hickup until about half way there. Started slamming in and out of gear trying to find what gear it should be in I guess. Hooked up HPTuners to try and flash back to stock transmission tune and could not connect to the TCM was getting an error. Let the car shit in the parking lot all day with the battery disconnected. After work I reconnected everything and tried to flash it again. This time it went thru all the motions it erased got aobut 30% into writing calibration and it lost connection and timed out. Tried to flash again with no luck just continually times out and now i have a U0101 code or something like that. Can not connect to it at all and the car stays in 2nd or 3rd gear all the time because it acts like i have a large torque converter when i start off and never shifts and to do 70 im sitting around 3k rpm to cruise at 70. I have also caught my speedo bobbing a little bit. Now my question is The TCM in the car is a 24231673, I can find some used on fleebay but what normally pops up when im looking for one is a 24226863. Is there a difference in these two? Can i use 24226863 ? If i do get one will i be able to flash it to the same tune file im already using? Any input is really appreciated.

  2. #2
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    The flash failed so you're in 3nd gear failsafe/limp-home mode as the TCM isn't actually controlling the trans right now and everything is at full line pressure. You probably also do not have a gear indicator on the cluster as well.

    Any aftermarket accessories like an alarm or stereo? Start pulling the Radio, Onstar fuses and retrying the flash. If you can't get it to flash, next best option would be to bench flash it quickly and then put it back in the car. If that doesnt work, then you're looking at a new TCM.

    T42s are pretty resilient, I've personally had good luck flashing different OS' in but I've only played with 06-08 model years.
    ~Erik~
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  3. #3
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    Quote Originally Posted by ScarabEpic22 View Post
    The flash failed so you're in 3nd gear failsafe/limp-home mode as the TCM isn't actually controlling the trans right now and everything is at full line pressure. You probably also do not have a gear indicator on the cluster as well.

    Any aftermarket accessories like an alarm or stereo? Start pulling the Radio, Onstar fuses and retrying the flash. If you can't get it to flash, next best option would be to bench flash it quickly and then put it back in the car. If that doesnt work, then you're looking at a new TCM.

    T42s are pretty resilient, I've personally had good luck flashing different OS' in but I've only played with 06-08 model years.

    Car does not have a gear indicator on the cluster. Could the problems I was having before it failed to flash be cause by it going bad? With the TCM not controlling anything the transmission feels fine granted its stuck in 3rd gear. Even if I get it to reflash Im worried Im still just going to have the problems I had before it failed to flash.

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    Quote Originally Posted by XeRoX17 View Post
    Car does not have a gear indicator on the cluster. Could the problems I was having before it failed to flash be cause by it going bad? With the TCM not controlling anything the transmission feels fine granted its stuck in 3rd gear. Even if I get it to reflash Im worried Im still just going to have the problems I had before it failed to flash.
    The failed flash is at least causing the loss of cluster indicator, 3rd gear default, and full line pressure.

    Not sure about the other issues, but you need to get the TCM programmed with a usable tune before proceeding with troubleshooting.
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned

  5. #5
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    Quote Originally Posted by ScarabEpic22 View Post
    The failed flash is at least causing the loss of cluster indicator, 3rd gear default, and full line pressure.

    Not sure about the other issues, but you need to get the TCM programmed with a usable tune before proceeding with troubleshooting.
    Once I get it re-flashed if i can then what should i do for trouble shooting? When it was wondering and shifting in and out of gears hard and erratically I wasn't getting any codes.

  6. #6
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    Quote Originally Posted by ScarabEpic22 View Post
    The failed flash is at least causing the loss of cluster indicator, 3rd gear default, and full line pressure.

    Not sure about the other issues, but you need to get the TCM programmed with a usable tune before proceeding with troubleshooting.
    TCM is flashed with stock trans tune again, it finally let me do it after letting the car sit for a couple weeks with the battery disconnected. Let it idle in the driveway for 10 mins, took it for a drive and after a couple miles it started acting up again. Speedo bouncing up and down a few miles per hour, up shifting and down shifting for no seemingly no reason and i think locking and unlocking torque converter. When it starts doing this it also start to bring the trans temp up and heat up faster than normal. Its not as harsh now with the stock trans tune but something still isnt right. I have replaced the vehicle speed sensor in the rearend and it has done nothing. The care doesnt have a gear indicator on the dash at all(it never did). Ill upload a video shortly of what the speedo is doing, I guess i didnt capture what the rpms are doing as it searches for gears so ill try to get a better video after work.

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    Have you logged it to see if this is a cluster issue or is the actual data over the bus show the MPH jumping around? Can you post the tune(s) and a datalog of this happening?

    Are you using the correct TCM OS for this year car? (and corresponding ECM OS)

    If the MPH/VSS jumps around, the TCM will try to react so Im not surprised it's up/downshifting and the TCC is cycling on/off.
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned

  9. #9
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    Quote Originally Posted by ScarabEpic22 View Post
    Have you logged it to see if this is a cluster issue or is the actual data over the bus show the MPH jumping around? Can you post the tune(s) and a datalog of this happening?

    Are you using the correct TCM OS for this year car? (and corresponding ECM OS)

    If the MPH/VSS jumps around, the TCM will try to react so Im not surprised it's up/downshifting and the TCC is cycling on/off.
    The weather is nice today so after work ill take it out and log it happening so that i can post them up. As far as i know the TCM and ECM should both have the factory OS on them. I replaced the vehicle speed sensor with a brand new acdelco in hopes of that solving the problem(it was the first thing i did) and it didnt seem to help at all. After i get home ill log the drive as soon as it starts happening and post it along with the tune file i am currently using. Once i managed to get it flashed after it got wiped and lost connection, i put the stock trans tune back in so thats what im currently running on.

  10. #10
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    So after about 35 minutes of driving it started again. Ran the DTC's and got U0101 and also a code for shift time/ solenoid high or some thing like that, that code disappeared when i reran the the DTC check when i made it home. It looks like it just completely loses communication with the TCM for seemingly no reason. Was logging gear indicator and it started showing invalid. Sorry for the long log file but if you skip ahead to 30 minutes thats where it loses comm.

    u1010.hpl
    corvette(Transmission Stock).hpt

  11. #11
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    Your STFTs start to swing wildly when the VSS starts jumping around.

    The ECM OS doesnt match what TIS says should be in your car, but looking at the repo it looks like GM released a handful of 05 Vette OS updates (not surprising since it was the first year of the E40/LS2 in the Vette). The TCM OS is the correct one, there is a newer version available for your car but I doubt it would fix this issue.

    Have you wiggled the TCM connector when it's working properly to see if there's a loose wire in the connector?

    You could throw a new TCM at it, might not be a bad idea at this point I'm afraid. Honestly though, I've seen more E40s fail than T42s...
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned

  12. #12
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    I had noticed that this drive that i logged and the last drive i did after i got the tcm reprogrammed that when it started messing up the motor felt weird as well. Do you know if the other part number i had posted about will work? The TCM is mounted in the passenger fender a long with the ecm and it only messed up after driving for a little bit some times sooner than others. I did put it on jack stands and took the tcm out of the car and the plug looked great nothing visually looked loose and all the pins looked good.

  13. #13
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    I meant wiggle the actual plug while it's installed in the car and the car is running to see if there's a loose connection that gets bumped when you drive.

    My experience has been that T42s are pretty robust and take whatever you flash into them. Most are like $20 on eBay so couldn't hurt to grab one and try it. Yes, you can flash your current tune, just make sure to Write Entire for the TCM.

    If the engine acts up as well, I'd really start looking more at the ECM than the TCM. The ECM is the module throwing lost comms with the TCM and the module causing the engine to act up, I'd check to see if the ECM is working properly. Unfortunately, the E40s are pricey as they were only used for 2 years.
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned