Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

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

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4 years 3 weeks ago #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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4 years 3 weeks ago - 4 years 3 weeks ago #38067 by John Curtis
Here is a TSB and diagrams of the data network.

What are all your codes?

Making Pressure Differential Sensors (PDA Sensors) for pressure pulse diagnostics.
Currently servicing Central Texas.
Last edit: 4 years 3 weeks ago by John Curtis.
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4 years 3 weeks ago #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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4 years 3 weeks ago #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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4 years 2 days ago #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?
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4 years 2 days ago - 4 years 2 days ago #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: 4 years 2 days ago by jreardon.
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4 years 2 days ago #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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3 years 10 months ago #39855 by Betterway52
hey there car is still beating me up. i have a capture on my pin 1 of dlc the low speed can network. which shows constant communication. hours after car has been off. i also noticed that the data from my radio on the scan tool does not match power mode of the bcm. the radio data will show power mode off with car running and radio is playing. i cycled the key and it sometimes changes to acc or to run, im thinking now its an ignition problem or the bcm is not sending signal sometimes to radio. i need to look over how that circuit operates. now with the pin 1 capture shouldnt the waveform be all squarewaves for communication like on the high speed can lines?

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3 years 10 months ago #39856 by Betterway52
These are the pin 1 waveforms. Low speed can. Any help ideas are appreciated and welcomed.
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3 years 10 months ago - 3 years 10 months ago #39869 by John Curtis
Missing termination resistor(inside the module).
you’ll see how the voltage is going too high for the can network specs?
As far as the location of the terminating resistor SI shows that on is internal to the PCM and the other is in the rear fuse box.

Making Pressure Differential Sensors (PDA Sensors) for pressure pulse diagnostics.
Currently servicing Central Texas.
Last edit: 3 years 10 months ago by John Curtis. Reason: Correcting myself with service information
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3 years 10 months ago #39891 by Betterway52
thank you. im not sure if it is a flood vehicle. i am going to monitor the signal and start attemting to unplug modules. was hoping i did not have to take dash apart to get to the instrument panel cluster but that appears to be where i may have to go.

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3 years 10 months ago #39967 by Cheryl
First what is the list of modules you can communicate with when no problem occurs? Compare that to the list when malfunction occurs. See if it’s the pins 6 and 14 that’s messed up or the single wire communication. I’m betting it’s the ebcm since it has an internal fault code. Unplug it jump the cam lines with jumper wires to bypassed the module.

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9 months 2 weeks ago - 9 months 2 weeks ago #61845 by Khanm83
I am having this same problem with a 2007 DTS.. was running fine .. then stopped running.. when I unhooked the battery and hooked it back up.. I am unable to get the car to start...

It's showing loss of communication with ecm bcm and a few other modules..

I am lost as go what the problem is.. I believe it's wiring that's shorted out or has gone bad somewhere...
Last edit: 9 months 2 weeks ago by Khanm83.

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