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:
- 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:
- 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:
- 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.
| • | Proper SERVICE 4WD indicator operation. |
| • | Ability of the transfer case shift control module to communicate through the data link connector (DLC) |
| • | Existence of FT4WD DTCs |
| • | Extended Diagnostic Time |
| • | Incorrect Diagnosis |
| • | Incorrect Parts Replacement |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
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A fuse failure will cause no communication this step has you check for this condition.
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This step determines if the fuse blows when the ignition is turned on.
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This step determines if there is a short to ground in the battery positive circuit causing the fuse to blow.
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This step refers to the table for DTC C0306 for further diagnosis if a transfer case mode change is causing the fuse to blow.
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The presence of DTCs indicates that the transfer case shift control module has detected a fault. Go to symptoms for other concerns.
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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.
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Vehicle speed is provided to the transfer case shift control module via Class 2 and can effect the setting of DTC C0300. Perform the diagnostics for powertrain DTCs P0502 and P0503 first.
Step | Action | Yes | No |
|---|---|---|---|
1 | Install a scan tool. Does the scan tool power up? | Go to Step 2 | Go to Scan Tool Does Not Power Up in Data Link Communications |
Does the scan tool communicate with the transfer case shift control module? | Go to Step 7 | Go to Step 3 | |
Did the TREC fuse blow? | Go to Step 4 | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications | |
Replace the TREC fuse. Does the ATC fuse blow immediately? | Go to Step 5 | Go to Step 6 | |
Check the battery positive circuit for a short to ground. Was the condition found and corrected? | Go to Step 2 | Go to Transfer Case Shift Control Module Replacement. | |
Did the TREC fuse blow? | Go to DTC C0306 | Go to Step 2 | |
Select the transfer case shift control module display DTCs function on the scan tool. Does the scan tool display any DTCs? | Go to Step 8 | Go to Symptoms - Transfer Case | |
Does the scan tool display any DTCs which begin with a "U"? | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications | Go to Step 9 | |
Does the scan tool display DTC P0502 or P0503? | Go to Applicable Powertrain OBD Diagnostic System Check |
