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2006 cadillac dts intermittent no com with few diff modules creating no start

  • Betterway52
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04 Mar 2020 15:31 #38063 by Betterway52
I have a 2006 cadillac DTS. The car has has various u codes. at times i can not comunicate with tcm,bcm,ecm,abs. i have checked the ohm on the dlc connector when i have no com and i read 63-64 ohms all modules connected.I have also checked the power and grounds to the modules with a test light did not go as far as to take voltage readings. whenever i disconnect any module the resistance jumps to 123ohms. which i think is supposed to be normal? if i pull up data from module with intermittent fault data will display and then shortly thereafter not comunicate. Any help would be greatly appreciated. any other test i could do would greatly be appreciated.

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04 Mar 2020 16:16 - 04 Mar 2020 16:16 #38067 by John Curtis
Here is a TSB and diagrams of the data network.

What are all your codes?

Thinking out loud always helps me in the process.
Last edit: 04 Mar 2020 16:16 by John Curtis.
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04 Mar 2020 18:59 #38075 by Betterway52
I have the wiring diagram thanks. i did not see this tsb i will check my module connectors for this condition. which i do not think is occurring.

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04 Mar 2020 19:04 #38077 by Betterway52
codes are u1000 u0073 c0550 b1325 c0899 u0100 probably some others. they always lead to a no com to different modules. but most seem as a loss to ecu

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25 Mar 2020 12:54 #38622 by Betterway52
These images are from the dlc and then the single trace images are the can lines at the connector. Any idea what that looks like bad computer?
Attachments:

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25 Mar 2020 16:35 - 25 Mar 2020 16:48 #38627 by jreardon

Betterway52 wrote: whenever i disconnect any module the resistance jumps to 123ohms. which i think is supposed to be normal?


I've redrawn that oe diagram just to make it easier to understand where the wires are going.



Last edit: 25 Mar 2020 16:48 by jreardon.
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25 Mar 2020 20:59 #38635 by jreardon
c0550 - ebcm detects an internal malfunction
c0899 - device voltage low - ignition voltage to ebcm is less than 9v for 100 msec.
b1325 - device power circuit - system voltage below or above the calibrated value of 9v -18v

Clear the codes, make sure battery is good and terminals tight. Check battery for excessive ac ripple. Check what your low speed serial data looks like (dlc pin 1). 60 ohms on high speed gmlan and your image attachment shows it's intact, not shorted to each other, not shorted to power nor ground. Scope capture looks a little wavy haha. c0550 points to bad ebcm, if that code keeps coming back unplug that module and jump the terminals so the 120 ohm resistor in the ECM stays connected on the network.
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