Circuit Description
This symptom usually occurs when a shift into or out of 4LOW will not occur. When the transfer case control module (TCCM) receives a request to shift into or out of 4LOW, the TCCM must see the following parameters before the shift routine can start:
| • | The vehicle speed must be below 3 MPH. |
| • | The transmission must be in neutral. |
If the TCCM does not see these conditions the shift control switch indicator lamp will flash for approximately 5 seconds and then return to the original gear.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests the operation of the transfer case shift control switch to help determine if the system is operating properly.
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This step determines if the vehicle speed sensor reading is correct.
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This step determines if the park switch reading is correct.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Transfer Case Control Schematics | ||||
1 |
Important: The transfer case shift control module is not a class 2 device, and therefore a scan tool can not be utilized on this transfer case. Did you perform A Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check |
Does the transfer case range change with the press of all of the shift control switch buttons? | -- | Go to Intermittents and Poor Connections Diagnosis in Wiring Systems | Go to Step 3 | |
Use the scan tool in order to read the vehicle speed sensor on the transmission control Data Lists. Is the vehicle speed within the specified range? | 0 km/h (0 mph) | Go to Step 4 | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 4.3L, Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 5.0L and 5.7L, Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 6.5L, or Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 7.4L | |
Does the scan tool indicate the transmission is in Neutral? | -- | Go to Step 5 | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 4.3L, Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 5.0L and 5.7L, Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 6.5L, or Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 7.4L | |
5 | Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement . Did you complete the replacement? | -- | Go to Step 6 | -- |
6 | Operate the vehicle within the conditions for causing the symptom as specified in the supporting text. Does the symptom re-occur? | -- | Go to Step 2 | System OK |
