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Discussion Starter · #1 ·
I think my tcm has gone bad. My 08 is an SS and the pull a parts around here don't have an SS. Will the Lt tcm be a direct replacement or does it need reprogrammed? Or if I just buy a new one from autozone will it need to be programed?
 

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You'll likely need to program a replacement.
Have you checked power and ground connections to the TCM?
Have you looked at the Class II databuss signal with a scope?
 

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Dr Shock video. SAE J2534 AC Delco service programming with a laptop and Blue GM Bosch MDI
You can buy a single VIN service programming license for @ $40 Yankee bucks

Viewing Class II Data signal with a scope. You will not get any meaningful information from a multimeter.
 

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Discussion Starter · #4 ·
You'll likely need to program a replacement.
Have you checked power and ground connections to the TCM?
Have you looked at the Class II databuss signal with a scope?
No I haven't done anything but run my code reader on it. Popped up code P0700 and after Google search it said thats a bad tcm. I'll check for power and good ground but the databuss signal thing I don't have the equipment for
 

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P0700 means is the TCM isn't communicating or is sending dodgy data.

No power and No / damaged Comms connection are the first place I look. If one or both are not OK then a good TCM can't talk. Much cheaper to fix corroded, broken, or chewed wire(s) or bad ground(s) than replacing a controller.

There are several power and ground wires on the ECM. I'd have to look at the TCM wiring diagram but don't count on only one pair of power wires.
Comms are twisted wires.
Use a tungsten filament bulb to test power and ground. A meter is low impedance so it'll show 12v when the wire is corroded or damaged enough that it won't carry enough current to light a 168 series peanut bulb.
 
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Discussion Starter · #6 ·
No I haven't done anything but run my code reader on it. Popped up code P0700 and after Google search it said thats a bad tcm. I'll check for power and good ground but the databuss signal thing I don't have the equipment for
P0700 means is the TCM isn't communicating or is sending dodgy data.

No power and No / damaged Comms connection are the first place I look. If one or both are not OK then a good TCM can't talk. Much cheaper to fix corroded, broken, or chewed wire(s) or bad ground(s) than replacing a controller.

There are several power and ground wires on the ECM. I'd have to look at the TCM wiring diagram but don't count on only one pair of power wires.
Comms are twisted wires.
Use a tungsten filament bulb to test power and ground. A meter is low impedance so it'll show 12v when the wire is corroded or damaged enough that it won't carry enough current to light a 168 series peanut bulb.
Checked for power at the tcm no power. Looked in fuse box found the 10a trans fuse was popped. Put in new fuse and soon as I turned key on popped again. I guess i got a short some where or can a bad tcm pop the fuse?
 

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Discussion Starter · #7 ·
Checked for power at the tcm no power. Looked in fuse box found the 10a trans fuse was popped. Put in new fuse and soon as I turned key on popped again. I guess i got a short some where or can a bad tcm pop the fuse?
So it still blows the fuse even when the tcm is unplugged so that eliminates that. My luck is its the shift solenoid in the transmission pan
 

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Fuse blowing without the TCM plugged in means you have a short to ground between the TCM and the fuse panel.
 
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Discussion Starter · #9 ·
So it still blows the fuse even when the tcm is unplugged so that
So it still blows the fuse even when the tcm is unplugged so that eliminates that. My luck is its the shift solenoid in the transmission pan
Fuse blowing without the TCM plugged in means you have a short to ground between the TCM and the fuse panel.
Not my transmission but its same 07 ss mine is 08 ss. Do you happen to know what that plug is? When that is unplugged and key on fuse don't blow. Car won't start without it plugged in though
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Yep you was right. Took awhile but found the short between tcm and fuse box. Thanks for the help
Glad I could help and you found it. And thank you for the after action report.

Divide and conquer. I try to unplug components and harness interconnects when I'm chasing gremlins. It eliminates the components and sections of the wiring from my tests when I'm chasing a short or open or harness damage.
Eric at South Main Auto talks about the splitting things up method to chase shorts and open wires in long or complicated or obstructed wiring harness runs cause it cuts way down on time spent chasing the problem. Even when you're not costing a customer money and or pushing other jobs out on the schedule it's nice to get it done so you can go spend time with the family and use the darn car.
 
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