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i've got a 2006 Cadillac DTS. story was owner had drove x2 weeks. died now its ours to repair, I see No communication on ecm tcm or Bcm. tried to access them with my AUTEL 900 device, i tried to run active testing. checking for codes, it all said no communication. ABS and trac and engine light is on. no shift indicator on dash. No crank no start. so far ive jumped starter relay and engine cranks. ECU has 12V going to it. I had a oxy fuse blown. ign fuses ECM PCM TCM fuses and AFT seating and FWD fuses have. Fuel pump works. Have 5V ref at MAF and MAP also found 12V there. my next stop is testing Electric TB. Do i have a smoked ECM? Can they be opened to look inside for burns? I see the TCM is getting hot to touch i cleaned curosion on the tcm connector. ecm cool to the touch. nothing melted on harness that i seen.
Hi,
If you have a no communication situation with various control units then I would start by checking the CAN network signals.
There are various issues that could cause CAN issues.
I agree with Rupert, I would probably start by checking the resistance of the network on pin 6&14 of the data link connector.
Unless you really did find 12v at the MAP connector, I am assuming you only found 12v at the MAF, but the way it's written makes it appear as both have 12v.
Will checking resistance at the OBD socket actually measure the high speed CAN network? Depending on topology you may only be communicating scan data with an interface. My preference would be to scope the CAN wires at one of the control modules that have a ‘no com’ issue.
You are correct, depending on the network topology, measuring resistance at the data link connector won't always work.
However, I did look at the network diagram before suggesting testing at the DLC, and on this car, there is no gateway or interface to complicate things.
So I can go to the ECM and check resistance what pens what I need to check for 60 ohm resistance? Also the TCM and BCM have no communication I'm thinking maybe the security key might not be working but the security light turns off when the ignition is on
Doesn't sound like a security issue to me, you would still be able to communicate with all the modules but the car wouldn't run.
I personally would check resistance at pins 6&14 of the data link connector under the dash, preferably with the battery disconnected.
As Rupert rightly suggested, if you have a scope and wire diagram you can always scope the HS CAN wires at modules.
So I need 60ohm with the battery disconnected? What would I do if it's not in spec, do I disconnect each module until I get 60ohms? I suspect the TCM is bad I saw corrosion in connection and wire pins. it's getting hot with the battery plugged in the car has a drain on the battery also it drops to 12.3 with the key on headlights off
If you are suspecting the TCM, you can bypass it by splicing the data wires.
Tan/black to tan/black and tan to tan.
It probably still won't start but if you regain communication with the rest of the modules then you found your problem.
Woe baby! I measured with the TCM disconnected and have 120ohm. I plugged in and still have 120 ohm. I pulled the green resistor in rear seat and it reads open. Does this mean a different module is shorted if I don't get 60ohm?
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