Cadillac cts 03 wont shift out of park

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03 cts module. Ecm was replaced and the car wouldn’t shift out of park. So I replaced the ecm that was under warranty. But I’m getting the same problems with new ecm. Abs/brake/traction lights all onThis is the code I getP0856 How can I find out if it’s a wiring harness open or a faulty ebcm? 

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Ilaria17 4 months 5 Answers 904 views Member 0

Answers ( 5 )

  1. Hello

    To get this from the beginning.

    1. Do you get contact with the diagnostic computer to the Engine(ECM), Brake control module, Transmission module? If not check fuses/if you got 12volts to the ecus.
    2. Do you have brake lights?
    3. In which control module are you getting the trouble codes?
    4. Make sure the variant coding in the ECU’s is OK as I mentionded before.
    5. Check Live data in the TCM(transmission control module). Check that the brake light switch is OK from there, check what gear the tcm gets from the shift module. It should say “P”
    6. Try to do “output test” to the shift module solenoid. To see if it releases when you do it with the computer.
    7. check the same live data in ecu/bcm to see where the information gets lost.

    I think you should check this things before you start to search for wiring faults.

    Best answer
  2. This answer is edited.

    I do have working brake lightsThe trouble codes I’m getting are coming from ECM P0856. P0161. P0056.  P0318 

  3. Okay like I said, you have to make sure that you got communication with the Transmission control module and brake control module and read the fault codes there, and check live data.

    If you dont have communication you have to check if you got 12v+ and ground to them.


  4. I don’t know how to do any of the tests you are advising to perform

  5. You need a good diagnostic tool for this job. You have to check which ecu’s you have communication with and can search for trouble codes in 🙂

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