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<H1>4WD Switch Indicator Lights Flashing, 4WD Inoperative, DTCs C0327, P0836, P0500 (Replace Encoder Motor Sensor, Reprogram TCCM, Inspect Front Drive Axle Engagement Sleeve for Damage/Repair if Necessary #03-04-21-001C - (06/24/2003)</H1></TABLE>4WD Switch Indicator Lights Flashing, 4WD Inoperative, DTCs C0327, P0836, P0500 (Replace Encoder Motor Sensor, Reprogram TCCM, Inspect Front Drive Axle Engagement Sleeve for Damage/Repair if Necessary)


2003 Chevrolet Avalanche, Silverado, Suburban, Tahoe


2003 GMC Sierra, Yukon, Yukon XL


This bulletin is being revised to update the Correction and Warranty Information. Please discard Corporate Bulletin Number 03-04-21-001B (Section 04 -- Driveline/Axle).<A name=ss1-1350313><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1350313&psdid=297&evc=sm#ss1-1350313" target="_blank">
<H5>Condition</A></H5>


Some customers may comment that the Service 4WD light is on, the 4WD system is inoperative, the 4WD switch indicator lights are blinking or that a grinding noise is heard from the front axle.<A name=ss2-1350313><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1350313&psdid=297&evc=sm#ss2-1350313" target="_blank">
<H5>Service Diagnosis</A></H5>


Technicians may find DTC C0327 in the Transfer Case Control Module (TCCM) and/or DTC P0836 in the Transmission Control Module (TCM) and/or DTC P0500 in the Powertrain Control Module (PCM).


It is possible that the module may be in a mode that will not allow any shifts or updates for the software or calibrations. If this occurs, the TREC fuse (in the engine compartment) must be pulled and reinstalled after 30 seconds. This should allow further operation and service of the system. If a C0550 code is found, the TCCM must be replaced. All other codes should be able to be cleared, and the module reused successfully.<A name=ss3-1350313><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1350313&psdid=297&evc=sm#ss3-1350313" target="_blank">
<H5>Correction</A></H5>



<H4>Important</H4>


For ease of reassembly, shift the transfer case assembly to 2HI for the NV263 (NP1), or Neutral for the NV246 (NP8) prior to removing any components. For information on placing the NV246 (NP8) transfer case in NEUTRAL, see the procedure at the end of this bulletin.




  1. <LI =1>Remove the transfer case and front axle/engine skid plates (if equipped).
    <LI =1>Disconnect and position the front propeller shaft aside.



    <LI =1>Disconnect the transfer case encoder motor wiring harness.
    <LI =1>Remove the three (3) bolts that retain the encoder motor to the transfer case.
    <LI =1>Separate the encoder motor assembly from the transfer case and place it on a work bench.






    <H4>Important</H4>


    DO NOT REMOVE THE SCREWS INDICATED WITH THE (1) IN THE ABOVE ILLUSTRATION.



    <LI =1>Remove the four screws on the outer perimeter of the encoder motor housing.



    <H4>Important</H4>


    For proper timing and ease of reassembly, hold the gear in place as your remove the cover from the encoder motor assembly with your thumb or finger.



    <LI =1>Carefully remove the cover from the encoder motor assembly. The cover has a sea
 
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