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Thread: 4l65 TCM will not command shift to 4th

  1. #1
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    Mar 2020
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    4l65 TCM will not command shift to 4th

    Hello all, Im a little new here so please be gentle with me LOL!
    Like the title says this TCM will never command a shift to 4th if engine is running. You can command all 4 gears with the engine off only. With the gear command test, the solenoids A and B respond and current gear pid changes and you can hear the solenoids click in the trans with engine off. 1, 2 and 3 all work fine but the TCM never trys to shift to 4th and the only way I can get 4th to ever happen is with engine off with scan tool or VCM scanner gear command test. Both tools gear commands do not command when engine running and only work when engine is off. PRNDL shows correct D4, VSS shows correct, no OD off input is present according to pids and it shifts up through 1,2 3 and back down 3,2,1 just fine but never will the tcm command 4th gear on its own? I have tried lowered RPM and VSS speeds with no luck at all. TCM never tries to shift to 4th even according to pids. Tune and data log attached if anyone can spot anything strange, I may not loose my mind........ today anyway! Gen 3 Camaro with 2008 truck 5.3 with 4l65e e38 with t42. Swap was done a few years ago, never finished and now its in my yard driving me slowly insane. 1st, 2nd and 3rd all work correct so with only 2 solenoids A and B that control all 4 gears, if the trans would command 4th it should go to 4th but TCM never does as data log shows
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  2. #2
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    Join Date
    Mar 2020
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    Looks like I found the pressure mode changing from "garage shift" to "diag test" and never leaves "diag test"? It also shows the shift mode pid as "unknown: 0b" most of the time and only "normal mode" under heavy acceleration in 1st and 2nd and as soon as it hits 3rd it again enters 'unknown 0b' ...........My gut says I found the problem and now to figure out the right fix. My neighbors must love me because this thing is LOUD and I've had it running WAY more than most! LOL!

  3. #3
    Potential Tuner
    Join Date
    Mar 2020
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    I found a map that had all the exact same id numbers in the trans hardware tab, all accept the diag tab and that tune is for a 4l80e and I know we have a 4l65e? The vin for the engine ecu im using for an 2008 1500 with a 5.3 and im assuming has a 4l60e. I did a segment swap to a stock 4l60e from a 2008 1500 5.3. The shift mode is now in "normal WOT' all the time and goes to "unknown: 0b" when wide open, when the old tune went to just normal and I still cant get 4th gear even with lowered speeds and rpm. Is this the wrong ecu to run a 4l65e and just will not work and I need a different tcm? Any way to figure out what tcm I need if this one won't work? I also noticed that before the segment swap the tcm was tripping iss faults so i disabled them. After the segment swap its not tripping iss faults and I haven't turned the faults back off like before the swap? If anyone has any insight in this I"m all ears on what I have to do to get this trans to shift correct. I'm not ready to give in yet! :]