Circuit Description
At each power-up, the transfer case shift control module runs a self-test on the following functions:
| • | Electronically erasable programmable read only memory (EEPROM) Checksum |
| • | Read only memory (ROM) Checksum |
| • | Random access memory (RAM) Checksum |
| • | RAM Malfunction |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C0550 ECU Malfunction
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The system voltage is 9-18 volts. |
Conditions for Setting the DTC
| • | Critical operational parameters stored in EEPROM have failed Checksum test indicating invalid data. |
| • | Masked ROM code has failed Checksum test indicating that masked ROM data is not currently valid. |
| • | ROM code has failed Checksum test indicating that ROM data is not currently valid. |
| • | One or more RAM locations have failed operational test indicating that some portions of RAM are not functional. |
Action Taken When the DTC Sets
| • | The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle. |
| • | The transfer case control switch does not display the current position LED while DTC C0550 is current. |
Conditions for Clearing the DTC
| • | Replace the transfer case shift control module. |
| • | Perform the Diagnostic System Check - Vehicle in Vehicle DTC Information. |
Diagnostic Aids
Extremely low system voltage can cause this DTC to set falsely. Refer to Battery Charging in Engine Electrical.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step has the technician attempt to reprogram the transfer case shift control module.
-
This step has the technician replace and reprogram the transfer case shift control module.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Transfer Case Control Schematics Connector End View Reference: Transfer Case Control Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Attempt to reprogram the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Does the DTC set after programming? | Go to Step 3 | System OK | |
Replace the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the repair? | System OK | -- | |
