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5 Answers

Cadillac cts 03 wont shift out of park

Asked by: 37 views Transmission question

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?


5 Answers

  1. 0 Votes Thumb up 0 Votes Thumb down 0 Votes


    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.

    Ask A Mechanic Admin - Dec 25, 2017 |Reply

  2. 0 Votes Thumb up 0 Votes Thumb down 0 Votes

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

    Ilaria17 - Dec 25, 2017 |Reply

  3. 0 Votes Thumb up 0 Votes Thumb down 0 Votes

    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.


    Ask A Mechanic Admin - Dec 26, 2017 |Reply

  4. 0 Votes Thumb up 0 Votes Thumb down 0 Votes

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

    Ilaria17 - Dec 27, 2017 |Reply

  5. 0 Votes Thumb up 0 Votes Thumb down 0 Votes

    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 🙂

    Ask A Mechanic Admin - Dec 27, 2017 |Reply

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