Converter or ECM problem?
- Thread starter jbird007
- Start date
Replaced. Logged and traced wires to ECM and TCM to confirm brake status - checked out OK.
Ok, A40 LBZ TCM fixes the problem!! But, creates more problems as well. The converter locks HARD, I'm guessing this because of the absence of the engine speed sensor? Also, tow/haul and tap shift don't work. With the A40 from an LMM the trans unlocks the converter (same problem) and doesn't downshift into 1st until fully stopped for 2-3 seconds (T/H and tap shift work). Thought about splicing / re-pinning the LMM harness to comply with the LBZ TCM, however, that won't fix the lack of speed input. The underhood fuse panel came from a 2wd truck - Are the 2wd/4wd fuse panels different? Maybe I have a GMLAN in the incorrect place? When swapping we took the suburban panel out and put the 2wd truck one in and placed the harnesses (underneath) in their respective locations according to a "truck".
Maybe check with ferminator. I think he had the same issue. Also in a swap, but iirc it's a 5speed lb7
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You don't have an engine speed sensor? How does it know when to even lock up
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Try running a lockup controller. Part throttle lockup will most likely be a problem unless you get Ben to work some kinda magic though.
Lockup controller is not the answer...its a bandaid, and a poor one at best.
I still think there is a speed sensor issue. And you're absolutely sure you've checked brake pedal status as reported by the BCM, ECM, and TCM?
What scan tool are you using??
I still think there is a speed sensor issue. And you're absolutely sure you've checked brake pedal status as reported by the BCM, ECM, and TCM?
What scan tool are you using??
I wish I was local...Id love to take a look at it. Sometimes these more complicated gremlins really need to be diagnosed in person.
How does it even know when to lock without seeing rpm?!
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01-07 had both. The converter sensor was removed on the LMM's (07.5). You are correct though, the ECM sends the TCM RPM data from the crank sensor on the LMM.
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I didnt say the sensor wasnt reading at all, I said maybe theres an intermittent issue that is giving the TCM an erratic reading...it jumps around a bit.
It sounds like the TCM is in default mode for some reason.
Check the turbine speed sensor and output speed sensor for proper orientation and the wiring going to the sensors.
As said above, the 2007.5+ trucks do not use an input speed sensor (the one on the bell housing).
Ben
>100k
V2 and Tech2 emulator via MDI. I agree that it's a speed problem. A40 (LMM) in it now and unlocks converter and doesn't shift into 1st until stopped for 2-3 seconds. It seems as if the trans "lets go" in between upshifts(flares).
Turbine speed and output speed look normal, TCCM speed looks good as well. Any other PID's I need to look at?
Matched when locked and wasn't erratic. I never compared to another truck though. What should the readings be?
07-08 Duraburb - same shifting symptoms did you solve?
Hey,
I have an 07 gmt900 LMM Duraburb with the same symptoms. Did you find a solution?
It also harsh shifts into 1 when braking hard. It seems to over Rev w/out power at wot, I "false neutrals/gear hunts" over big bumps and so on.
Thanks!!
Hey,
I have an 07 gmt900 LMM Duraburb with the same symptoms. Did you find a solution?
It also harsh shifts into 1 when braking hard. It seems to over Rev w/out power at wot, I "false neutrals/gear hunts" over big bumps and so on.
Thanks!!