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  1. #11

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    Quote Originally Posted by silverado002 View Post
    I believe it may be using the vehicle speed sensor in the trans too.
    Actually, there may be two sensors. One is used by the transfer case when you have it in AUTO4x4 and the other (I think) is used by the ABS. I don't know which one provides the vehicle speed (which is based upon driveshaft rpm).
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  2. #12

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    C0225 is left front wheel speed sensor open. ABS system runs a diagnostic "test" (basicly sends a voltage through the circuit to see everything is operational) every time the key is turned on. if a code sets as soon as you turn the key on it is a "hard code", happening right now. check to make sure it is plugged in and wires/ connector are ok. check resistance of sensor with it unplugged. the U code are for communication. B code is SRS code. several modules must communicate together (class 2 serial data) for the system to work properly. you need to drive it and see if any codes return. if so these will help you locate your problem.
    OOH! almost forgot, check you fuses.

  3. #13
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    Quote Originally Posted by edsmagichands View Post
    C0225 is left front wheel speed sensor open. ABS system runs a diagnostic "test" (basicly sends a voltage through the circuit to see everything is operational) every time the key is turned on. if a code sets as soon as you turn the key on it is a "hard code", happening right now. check to make sure it is plugged in and wires/ connector are ok. check resistance of sensor with it unplugged. the U code are for communication. B code is SRS code. several modules must communicate together (class 2 serial data) for the system to work properly. you need to drive it and see if any codes return. if so these will help you locate your problem.
    OOH! almost forgot, check you fuses.
    PIKEY POSTED THE complete c0225 GM shop manual explanation. recheck your front sensor comment.

    This is the rear sensor being the issue . I also have the shop GM manual and this where I got my help info that the PCM is seeing a higher voltage at this sensors output.

    where did you get your front sensor info c0225 ?

  4. #14

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    Thanks j cat, keep me on my toes!

    I read Pikey's post, checked against MOD, appears to be the same info. all the codes mentioned are speed sensor codes. 221 & 225 conditions for running DTC is key on. this tells me it's part of the ECBM's self test. conditions for setting 221 & 225 are open or shorted wheel speed sensor or circuit for 500 milliseconds, (not high voltage). MOD shows this truck as a 3WAL not 4WAL. meaning rear wheel speed is monitored by the VSS. since C0221 & C0225 were grouped together,and no "P" codes for VSS, i figured they were for front rt & lt speed sensors. MOD nor Pikey's info clarified this. http://www.obd-codes.com/trouble_cod...codes.phplists C0221 as right front & C0225 as left front.

    This is interesting! i would love to read your GM shop manual as it seems we have conflicting info. which by the way, wouldn't be the first time i've seen it. i will certainly review my data for accuracy but, as of right now, it makes sense to me.

    The presence of all those speed sensor codes along with the "U" & "B" codes leads me to suspect a module communication/failure may be present.

    Again, feel free to correct me if i have mis interpreted my data.

  5. #15
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    pikey and I have the same info , should be the rear sensor to high on voltage...

    just hope that he can post back so others can be helped with his findings. ABS can be tricky and a tough ,expensive rear.... actually it is normally an expensive repair.. if it is a sensor in the rear then that would be the cheapest fix..

  6. #16

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    I just reread this thread start to finish. no where in pikey's post does he indicate it's the rear sensor or it's high voltage. "Conditions for Setting the DTC
    C0221 and C0225
    The EBCM detects an open or shorted wheel speed sensor or wheel speed sensor circuit for 500 milliseconds." that's from his post. what am i missing?

  7. #17

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    I Don't know if this will help but there is a service bulletin describing an ABS light on condition. While the codes aren't exactly the same I think it could be like edsmagichands describes as a BCM comm failure.
    "The presence of all those speed sensor codes along with the "U" & "B" codes leads me to suspect a module communication/failure may be present."

    Bulletin No.: 04-05-25-002E - 1999-2007 Silverado ClassicSome customers may comment that the ABS light is on. Upon further inspection, DTCs C0265 and C0201 may be set in the brake module. It is also possible for DTC U1041 to set in other modules. There may also be a loss of communication with the brake module.
    Cause:
    A poor connection at the EBCM ground is causing unnecessary replacement of brake modules. The EBCM ground is different for each application. Fullsize Trucks and Utilities = Ground 110. Remove the EBCM Ground. The EBCM Ground is located on the frame beneath the driver's side door. If multiple grounds are found in this location, the EBCM ground can be identified as the heavy (12-gauge) wire. Clean and reconnect.
    I don't wish to lead you down the wrong path but it may be something to consider.

  8. Thanks edsmagichands thanked for this post
  9. #18

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    Well said silverado.

    I was saving that for later! the Electronic Brake control Module (EBCM) ground wire is a common problem in this year range. all the codes mentioned could be a result of this ground being loose/corroded. the fact that C0225 returned after battery was disconnected then reconnected and key turned on, suggests that there may also be a bad left front speed sensor. communication between modules can be verified with the correct scan tool. a good test drive is still needed to see if any codes return.

    If i were diagnosing and repairing this vehicle with the info given, i would check resistance of both front wheel speed sensors, replace if bad, clean & reconnect the EBCM ground, test drive & see if any code return. as there has been no clear evidence otherwise, i stand by code C0225 as left front wheel speed sensor open or shorted.

    - - - Updated - - -

    forgot to say i'm glad someone was seeing what i was seeing.

  10. #19
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    the rear sensor I posted as the problem area is from the same pages pikey got the post he posted. the GM shop manual states this higher than normal voltage from the rear sensor with only this code of c0225.

    looking this code failure on the internet it is stated this is the LF wheel sensor... book wrong ?? could be .. with the high voltage it could be the ECBM or the ground on the frame rail next to the ECBM...

  11. #20

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    Well j cat, that IS interesting. if i understand you correctly, there is info in the GM manual,other than what pikey posted, that says if C0225 appears by itself it is high voltage from the rear sensor? that does seem to be a conflict in the GM manual since the page pikey posted clearly states the conditions for setting C0225 are open or shorted wheel speed sensor or circuit. i would love to read that manual. usually there will be a different code for opposite conditions on the same sensor.

    That being said, the web address i posted was not my only source of info. several professional techs who have personally repaired this code agree. C0225 is left front wheel speed sensor open or shorted. MOD says EBCM uses VSS as the reference for rear wheel speed. if C0255 were for the rear sensor i would expect to see a "P" code for VSS as well.

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