Check Engine Code U 0100
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Cadillac STS Forum - 2005 through 2012 Discussion, Check Engine Code U 0100 in Past Cadillac Vehicle Discussion; Took a run to the post office and during the ride the check engine light came on, I decided to ...
  1. #1
    tomm's Avatar
    tomm is offline Cadillac Owners Connoisseur
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    Check Engine Code U 0100

    Took a run to the post office and during the ride the check engine light came on, I decided to not shut it off when I got there (Good Thing) and the DIC started reporting all sorts of errors while driving check stability, cant initiate radar sensor or something similar etc. and when I returned home I shut off the STS and figured I would restart to see if check engine light would come back on.

    Guess What... Nothing, Would not crank or start everything went dead.

    Did a Google search and first recommendation was to disconnect the positive battery and ground it to restart the computer and sure enough it did the trick and it started right back up. Took it for a drive and everything was back to normal.

    Anyone have this problem before? U0100 Lost Communication With ECM/PCM?

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  3. #2
    1BadCadSTS's Avatar
    1BadCadSTS is online now Cadillac Owners Connoisseur
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    Re: Check Engine Code U0100

    Hey Tomm
    heres anything and everything GM says about it

    Document ID# 1423498
    2005 Cadillac STS


    --------------------------------------------------------------------------------

    DTC U0100-U0299
    Circuit Description
    Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

    DTC Descriptors
    This diagnostic procedure supports the following DTCs:

    DTC U0100 Lost Communication With Engine Control Module (ECM)
    DTC U0101 Lost Communication With Transmission Control Module (TCM)
    DTC U0104 Lost Communication With Distance Sensing and Cruise Control (DSCC) Module
    DTC U0121 Lost Communication With Electronic Brake Control Module (EBCM)
    DTC U0141 Lost Communication With Instrument Panel Module (IPM)
    DTC U0181 Lost Communication With Dynamic Headlamp Leveling (DHL) Control Module
    This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

    DTC Symptom
    DTC Symptom Descriptor

    00
    No Additional Information


    Conditions for Running the DTC
    Voltage supplied to the modules is in the normal operating voltage range.
    The vehicle power mode requires serial data communication to occur.
    The DTC U0001 does not have a current status.
    Conditions for Setting the DTC
    A supervised periodic message that includes the transmitter module availability has not been received.

    Action Taken When the DTC Sets
    The module uses a default value for the missing parameter.

    Conditions for Clearing the DTC
    A current DTC clears when the malfunction is no longer present.
    A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
    Diagnostic Aids
    A poor connection at the inoperative module may cause this code to set.
    An improperly powered module may cause this code to set.
    Step
    Action
    Yes
    No

    Schematic Reference: Data Link Connector (DLC) Schematics

    Connector End View Reference: Master Electrical Component List in Wiring Systems

    1
    Did you perform the Diagnostic System Check - Vehicle?
    Go to Step 2
    Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

    2
    Did you record any DTC in the range of U2105-U2199?
    Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information
    Go to Step 3

    3

    Important
    Use the DTC list in DTC Descriptors to determine which module is not communicating.


    Test the following circuits of the module that is not communicating for an open or a short to ground:

    The battery positive voltage input circuits
    The battery positive voltage output circuits
    The ignition voltage input circuits
    The ignition voltage output circuits
    The switched battery positive voltage circuits
    Refer to the following:

    Control Module References for the applicable schematic
    Circuit Testing in Wiring Systems
    Wiring Repairs in Wiring Systems
    Did you find and correct the condition?
    Go to Step 8
    Go to Step 4

    4
    Turn OFF the ignition.
    Test the ground circuits of the module that is not communicating for an open. If the module is the body control module (BCM), test its class 2 serial data circuit for an open, also.
    Refer to the following:

    Control Module References for the applicable schematic
    Circuit Testing in Wiring Systems
    Wiring Repairs in Wiring Systems
    Did you find and correct the condition?
    Go to Step 8
    Go to Step 5

    5
    Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing and GMLAN Wiring Repairs in Wiring Systems.

    Did you find and correct the condition?
    Go to Step 8
    Go to Step 6

    6
    Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits:

    The battery positive voltage input circuits
    The battery positive voltage output circuits
    The ignition voltage input circuits
    The ignition voltage output circuits
    The switched battery positive voltage supply circuits
    The ground circuits
    The high speed GMLAN serial data circuits
    Refer to the following:

    Control Module References for the applicable schematic
    Testing for Intermittent Conditions and Poor Connections in Wiring Systems
    Connector Repairs in Wiring Systems
    Did you find and correct the condition?
    Go to Step 8
    Go to Step 7

    7
    Replace the module that is not communicating. Refer to Control Module References for replacement, setup, and programming.

    Did you complete the replacement?
    Go to Step 8
    --

    8
    Use the scan tool in order to clear the DTCs.

    Does the scan tool still display other current DTCs?
    Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
    --





    Hope this helps, if I had to guess id say you have a bad ground or perhaps a dead cell in your battery.

  4. #3
    D&Ds_STS is offline Cadillac Owners Member
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    Re: Check Engine Code U0100

    Quote Originally Posted by 1BadCadSTS View Post
    Hope this helps, if I had to guess id say you have a bad ground or perhaps a dead cell in your battery.
    +1. Get your battery load tested. I had a similar bout of insanity that was resolved by replacing the car battery. I hope. So far, so good.

  5. #4
    lopezutos1 is offline Awaiting Email Confirmation
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    Re: Check Engine Code U0100

    hey when you grounded the positive battery to restart the computer where did you did that.?

  6. #5
    carter's_sts is online now Cadillac Owners Connoisseur
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    Just disconnect both cables from the battery and touch them together for a few seconds. Many people on here have done it.

  7. #6
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
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    Re: Check Engine Code U0100

    It's the standard reset procedure.

  8. #7
    ECSMALLS is offline Awaiting Email Confirmation
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    Re: Check Engine Code U0100

    Hello I have a 2006 Cadillac. My car does the same thing as listed above. What should I do. My car would not start and the code is U 0100 lost comm with ECM/PCM Module A. I need help
    Please PM me with any info

    Thanks

  9. #8
    Guy.Seminerio is offline Cadillac Owners Connoisseur
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    Re: Check Engine Code U0100

    Read the advice given above. Try that stuff and let us know if it works.

  10. #9
    Restomod is offline Awaiting Email Confirmation
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    Re: Check Engine Code U0100

    Hi Folks new here. having same issue as above. Has there been a fix? on the second battery same issue.
    did all the steps above. about to take to dealer for repairs just want to know if anyone has found a solution without expensive dealer repairs.

  11. #10
    Cadillac Cust Svc's Avatar
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    Re: Check Engine Code U0100

    Hello Restomod,

    Welcome to the forum! I am sorry to hear of the vehicle issue you've encountered. If you would like my assistance throughout the process of working with your dealership, please let me know. I can be reached via private message to further discuss your situation and help anyway that I can.

    Sincerely,

    Laura M.
    Cadillac Customer Care

  12. #11
    Diesel Dennis is offline Cadillac Owners Member
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    Re: Check Engine Code U 0100

    I have a 2004 CTS with the same code. Car sat for about three months but was running fine when I parked it.
    Went to start it the other day and it was electroniclly dead and would not start battery was completly dead no lights etc.
    It was the original battery so I replaced it. Now I have power but the security system will not allow the car to crank and you have to manually release the key.
    Called my dealer and they said I need to have the ECM relearned for $150 plus tow charge so the car will reconize the key.

    Does anyone know of a way to relearn the ECM so it reconizes the keys without spending $250 to take it to the dealer?

    (I have tried disconnecting the cables and touching together, removing ECM fuse and leaving key on for 5 min then replacing unpluging TCM and ECM all no help.)

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