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CAN Resistance measurement question on bad TCM

  • Jayband
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05 Jun 2019 16:35 - 05 Jun 2019 16:40 #30421 by Jayband
Had a 2009 cts 3.6 with recent transmission change that would not start and had no comm to ecm and tcm. Measurements show below.

Im still fairly new at this. Is there a reason why when i flip my meter leads the resistance measurement changed? Obviously i know its not good ill post the pics of when we disconnected the tcm.
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Last edit: 05 Jun 2019 16:40 by Jayband.

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05 Jun 2019 16:36 - 05 Jun 2019 16:39 #30422 by Jayband
This is when we disconnected the transmission which has the tcm in it. Good after that
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Last edit: 05 Jun 2019 16:39 by Jayband.

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  • cheryl hartkorn
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05 Jun 2019 19:01 #30427 by cheryl hartkorn
Replied by cheryl hartkorn on topic CAN Resistance measurement question on bad TCM
you had some weird measurments in the first post. was the network still active when you took those resistance readings?? i usually do mine with the battery unhooked for a few minutes. the 120 ohm reading is what id expect to see with the tcm removed as it most likely has a terminationg resistor in it. you should see either 60 or 120 ohms. but 60 is what you want to see

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05 Jun 2019 19:03 #30428 by cheryl hartkorn
Replied by cheryl hartkorn on topic CAN Resistance measurement question on bad TCM
just make sure to check all powers and grounds at the tcm since the transmission was removed a main ground might bolt on the trans it self

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  • Jayband
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05 Jun 2019 20:27 #30429 by Jayband
So the first post was with the transmission connected. No comm to ecm or tcm and no crank. Then i did those resistance checks and scope. I thought it was weird how one way i hooked up my meter leads gave me one resistance then i flipped it and gave me a different reading. And yes it was with network not active.


The second post was when i disconnected the transmission and the network looked good again on the scope. I did the resistance readings again of course planned to see about 120ohms since the tcm was disconnnected and it was there both ways i connected my ohm meter leads.

My question was how or why when the bad tcm connected there was two different readings when i flipped my meter?

Oh and to verify the used transmission we got had a bad internal tcm, we raised the old transmission close enough to just connect the old transmission and the network was good resistance was 60ohms and it fired up.

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