A Diagnostic System Check

Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
2. 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.
3. The presence of DTCs indicates that the transfer case shift control module has detected a fault. Go to symptoms for other concerns.
4. The presence of DTCs which begin with 'lull indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
5. 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.
6. Perform diagnostics for DTC C0300 and C0305 first before addressing other DTCs. DTC C0300 and C0305 can be responsible for setting other DTCs.