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<H1>Diagnostic System Check - Transfer Case</H1>


These diagnostic procedures will help you to find and repair full time 4WD
transfer case (FT4WD) system malfunctions. This service category also contains
information for repairing FT4WD system malfunctions. For best results, use the
diagnostic tables, and follow the sequence listed below:</P>

1. <LI type=1>Perform the Transfer Case Diagnostic System Check. All FT4WD
   diagnostics must begin with the Transfer Case Diagnostic System Check. The
   Transfer Case Diagnostic System Check determines the following:
   <UL type=BULLET>
   <LI>Proper SERVICE 4WD indicator operation.
   <LI>Ability of the transfer case shift control module to communicate through the
   data link connector (DLC)
   <LI>Existence of FT4WD DTCs </LI>

<LI type=1>Refer to the diagnostic table as directed by the Transfer Case
Diagnostic System Check. The diagnostic tables will help enable you to diagnose
any FT4WD system malfunction. Bypassing these procedures may result in the
following:
<UL type=BULLET>
<LI>Extended Diagnostic Time
<LI>Incorrect Diagnosis
<LI>Incorrect Parts Replacement </LI>[/list]<LI type=1>Repeat the Transfer Case Diagnostic System Check after you perform
any repair or diagnostic procedures. This will verify that you correctly
performed the repair. This will also ensure that other malfunctions do not
exist. </LI>[/list]<A name=ss1-836901><A href="#ss1-836901">
<H5>Test Description</A></H5>


The numbers below refer to the step numbers on the diagnostic table.</P>

1. <A name=TD02>
   <LI value=2>
   
   
   Lack of communication may be due to a partial malfunction of the class2
   serial data circuit or due to a total malfunction of the class2 serial
   data circuit. The specified procedure will determine the particular
   condition.</P><A name=TD03>
   <LI value=3>
   
   
   A fuse failure will cause no communication this step has you check for this
   condition.</P><A name=TD04>
   <LI value=4>
   
   
   This step determines if the fuse blows when the ignition is turned on.</P><A
   name=TD05>
   <LI value=5>
   
   
   This step determines if there is a short to ground in the battery positive
   circuit causing the fuse to blow.</P><A name=TD06>
   <LI value=6>
   
   
   This step refers to the table for DTCC0306 for further diagnosis if a
   transfer case mode change is causing the fuse to blow.</P><A name=TD07>
   <LI value=7>
   
   
   The presence of DTCs indicates that the transfer case shift control module
   has detected a fault. Go to symptoms for other concerns.</P><A name=TD08>
   <LI value=8>
   
   
   The presence of DTCs which begin with "U" indicate some other module is not
   communicating. The specified procedure will compile all the available
   information before tests are performed.</P><A name=TD09>
   <LI value=9>
   
   
   Vehicle speed is provided to the transfer case shift control module via
   Class2 and can effect the setting of DTC C0300. Perform the diagnostics
   for powertrain DTCs P0502 and P0503 first.</P></LI>

<TABLE width="100%" border=1>
<TBODY>
<TR>
<TH vAlign=bottom align=middle>


Step</P></TH>
<TH vAlign=bottom align=middle>


Action</P></TH>
<TH vAlign=bottom align=middle>


Yes</P></TH>
<TH vAlign=bottom align=middle>


No</P></TH></TR>
<TR>
<TD vAlign=center align=middle><A name=S01>


1</P></A></TD>
<TD vAlign=top align=left>


Install a scan tool.</P>


Does the scan tool power up?</P></TD>
<TD vAlign=bottom align=middle>


Go to Step2 </P></TD>
<TD vAlign=bottom align=middle>


Go to <A
href="/servlets/CellHandler?CellId=11032&RefDoc=836901&evc=sm">Sca n Tool
Does Not Power Up</A> in Data Link Communications</P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S02>


2 </P></A></TD>
<TD vAlign=top align=left>

1. <LI type=1>Turn ON the ignition, with the engine OFF.
   <LI type=1>Attempt to establish communication with the transfer case shift
   control module. </LI>

Does the scan tool communicate with the transfer case shift control
module?</P></TD>
<TD vAlign=bottom align=middle>


Go to Step7 </P></TD>
<TD vAlign=bottom align=middle>


Go to Step3 </P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S03>


3 </P></A></TD>
<TD vAlign=top align=left>

1. <LI type=1>Turn off the ignition.
   <LI type=1>Check the underhood TREC fuse. </LI>

Did the TREC fuse blow?</P></TD>
<TD vAlign=bottom align=middle>


Go to Step4 </P></TD>
<TD vAlign=bottom align=middle>


Go to <A
href="/servlets/CellHandler?CellId=11033&RefDoc=836901&evc=sm">Sca n Tool
Does Not Communicate with Class 2 Device</A> in Data Link
Communications</P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S04>


4 </P></A></TD>
<TD vAlign=top align=left>


Replace the TREC fuse.</P>


Does the ATC fuse blow immediately?</P></TD>
<TD vAlign=bottom align=middle>


Go to Step5 </P></TD>
<TD vAlign=bottom align=middle>


Go to Step6 </P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S05>


5 </P></A></TD>
<TD vAlign=top align=left>


Check the battery positive circuit for a short to ground.</P>


Was the condition found and corrected?</P></TD>
<TD vAlign=bottom align=middle>


Go to Step2 </P></TD>
<TD vAlign=bottom align=middle>


Go to Transfer Case Shift Control Module Replacement.</P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S06>


6 </P></A></TD>
<TD vAlign=top align=left>

1. <LI type=1>Start the Engine
   <LI type=1>Attempt to shift the transfer case to different modes.
   <LI type=1>Check the underhood TREC fuse. </LI>

Did the TREC fuse blow?</P></TD>
<TD vAlign=bottom align=middle>


Go to <A
href="/servlets/CellHandler?CellId=69972&RefDoc=836901&evc=sm">DTC
C0306</A> </P></TD>
<TD vAlign=bottom align=middle>


Go to Step2 </P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S07>


7 </P></A></TD>
<TD vAlign=top align=left>


Select the transfer case shift control module display DTCs function on the
scan tool.</P>


Does the scan tool display any DTCs?</P></TD>
<TD vAlign=bottom align=middle>


Go to Step8 </P></TD>
<TD vAlign=bottom align=middle>


Go to <A
href="/servlets/CellHandler?CellId=69979&RefDoc=836901&evc=sm">Sym ptoms
- Transfer Case</A> </P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S08>


8 </P></A></TD>
<TD vAlign=top align=left>


Does the scan tool display any DTCs which begin with a "U"?</P></TD>
<TD vAlign=bottom align=middle>


Go to <A
href="/servlets/CellHandler?CellId=11033&RefDoc=836901&evc=sm">Sca n Tool
Does Not Communicate with Class 2 Device</A> in Data Link
Communications</P></TD>
<TD vAlign=bottom align=middle>


Go to Step9 </P></TD></TR>
<TR>
<TD vAlign=center align=middle><A name=S09>


9 </P></A></TD>
<TD vAlign=top align=left>


Does the scan tool display DTCP0502 or P0503?</P></TD>
<TD vAlign=bottom align=middle>


Go to Applicable Powertrain OBD Diagnostic System Check</P></TD>
<TD vAlign=bottom align=middle>


Go to <A
href="/servlets/CellHandler?CellId=69963&RefDoc=836901&evc=sm">Dia gnostic
Trouble Code (DTC) List</A> </P></TD></TR></TBODY></TABLE>
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