Question about 2004 Cadillac CTS

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Had brake hose and electronic control module replaced on my 2004 Cadillac CTS . later (Two days) ABS light comes on . I don't know where the module is located and if replaced if it needs to be programmed.

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  • mrjameslewis Nov 10, 2010

    Well, we had cadillac to do the work and they have told us that the code indicates that the ABS may need to be replaced at 1300.00 they wanted to do more checking for additional money but we declined to give ourselvs some time to think.

    We had no indication of a problem when we took the car in for the hose replacement ( Cadillac recall for the hose) so we are find it strange that we suddenly have a 1300.00 problem.

    I'm sure it's possible but If I need to replace the ABS I'll need to know where to find it and If it needs programming.

    They were looking around for the reason the engine light was on and I had to tell them after I looked at the code report of the other mechanic, It pointed to the ECM.

    They told me I was incorrect and they needed to keep looking at 50.00 an hour only to call me back 5 minutes later with the news the ECM needed replacing.

    I am an electronic tech so I understand technical data.

    I just don't trust them.

    If I find that the unit needs replacing, I can find one on line but I need to know where it is located in the car so I can write down the specs to insure I order the correct box.

  • mrjameslewis Nov 10, 2010

    The codedes are: C0121

    The ECM is what was replaced not the ABS control module.
    The ABS T/C and Brake lamp came on two days later after Cadillac replaced the front brake hose and ECM module
    One code indicates a relay malfunction.
    The ECM and brake hose was installed at the same time.
    I took the car home and two days later the T/S, Brake ABS lamp came on.
    The fluid is filled.

  • mrjameslewis Nov 11, 2010

    Code: C0121

    Code: C0281

  • mrjameslewis Nov 11, 2010

    The (EBCM) electronic brake control module was not replaced, (ECM) the electronic control module was replaced because the engine light was on and I was getting faulty failure codes.

    The brake hose was also replaced at the same time. (Recall on hose Assy.)

    The ABS T/C and BRAKE control lamp came on two days after the hose Assy and the ECM was replaced.

    The repairs above may not be related to the ABS T/C , brake lamp coming on two days later but it just seems strange that the car is worked on for brake hose and ECM and two days later I have a major brake issue.

    The codes coming up are:



  • mrjameslewis Nov 13, 2010

    You are correct on all.
    Just One more question if you don't mind.
    Can a bad connection, ( open connection to the ebcm) give the same code 0121
    or does the code indicate closed circuit to the ebcm but malfunction from hte relay.
    I am specific because of my background and experience with electronics.

  • mrjameslewis Nov 13, 2010

    Thank you very much...


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I am not sure why the brake control module was replaced but it is located in the engine compartment on the right front fender.You will have to jack the vehicle up to get to it.Just follow the brake lines.The module has to be programmed after replacement.Also the brake pedal position sensor has to be calibrated.This has to be done at the dealership.The first thing you should do is get the codes and let me know what the code is.I can get back to you and let you know what the next step you should take.Just because the light is on does not mean you have to replace the electronic control module.That is why it is important to get the codes first.Hope this helps.Good luck.

Posted on Nov 10, 2010

  • Salvador Quintanilla Nov 12, 2010

    Good morning Mr.Lewis.I did some looking into the codes you gave me.The way I understand you when you say ecm you are meaning the ebcm.This is the electronic brake control module and it controls the anti-lock brakes.The ecm is for engine controls.If you are looking to repair the abs problem if you get an ecm you will get the wrong part.I want to make sure you get the correct part.The code co121 is a problem with a relay inside the ebcm and it is not serviceable.So the ebcm has to be replaced.Not a big job but it does have to be programmed and the brake pedal position sensor has to be calibrated.The code co281 is just an informational code for the technician.The ebcm is on the passengers side front fender area.You will need to remove the air deflector under the front of the vehicle.Hope this information has helped and let me know if you have anymore questions.Good luck.

  • Salvador Quintanilla Nov 13, 2010

    Yes it could be a bad connection,open or short .The diagnosis has you do an automated test and if the code reappears then they tell you to check the wiring and connections.So assuming the tech did that and it was all good then the only repair is to replace the ebcm.It`s good to know that you understand electronics so when I say an open circuit you know what I mean.That is a problem when answering peoples questions on here because you don`t know if they understand what you mean by an open,short or how a diode works.I hope this has been helpful and that your problem gets repaired.One thing I wanted to tell you about the 50 dollars an hour labor rate.At the dealership I was at it was 98 dollars an hour and that was about 5 years ago.Thank you for using fixya.


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Just check that the brake fluid level is ok, then you need to check that the ABS motor is also giving the brake system enough pressure. If these 2 areas are ok then you need to start looking at the sensors of the brake system.
Let me know, and I can give you more in-depth information.

Posted on Nov 10, 2010

  • Jason Maurirere
    Jason Maurirere Nov 10, 2010

    Possible Faults:

    1. You have an electrical connection fault to the Electronic Brake Control Module (EBCM), which is why your warning lamp is flashing.

    2. The brake pressure in the brake system has dropped which will also cause the warning light to come.

    3. Your brake fluid level is below the correct level.


    1. If you have had the warning light come on then you will have a fault code in the system, as you mentioned you got one from your last mechanic - Can you give me this code?

    2.If there is a electrical connection fault to the EBCM then the fault code will indicate this, if the fault code indicates this, then the faulty connection will need to be found.

    3. Make sure that you have the brake pressure tested, if is a fundamental step to isolating the fault to the ABS motor or modulator, it is also a recommendation from Cadillac.

    4. Once you have had the pressure test then you can determine weather the ABS needs to replaced.

    5. Check the fluid level and the fluid level switch, this maybe all that is at fault.

    Only until you have gone through this sequence, will it allow you to make certain that the fault is within the ABS modulator, the worst thing you can do is start replacing parts without having the facts that that part needed replacing.

  • Jason Maurirere
    Jason Maurirere Nov 11, 2010

    Both these codes are actually relevant to each other, when a code C0121 is set then this will also set the C0281 code and vice versa.
    What needs to be done is the DTC needs to be cleared with a scan tool, then once this is done a ABS systems check with the scan tool needs to be done.
    If the DTC or codes then show up again on the scan tool after the ABS system check the following procedure needs to be done.
    1. The Pump motor solenoids need to be check for continuity.
    2. If the value is open circuit then you need to replace the ECBM
    3. If the value is not open then you need to replace the BPMV - Brake Pressure Modulator Valve

    Once this is done you can then rescan the ABS system and see if any other codes come up, after doing the above the codes should not come up.


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