For 1990-2009 cars only
Circuit Description
At each power-up, the transfer case shift control module runs a self-test on the following functions:
| • | EEPROM Checksum |
| • | ROM Checksum |
| • | 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 9-16 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. |
| • | Transfer case shifting is disabled. |
Conditions for Clearing the DTC
| • | Replace the transfer case shift control module. |
| • | Perform the Diagnostic System Check - Vehicle. |
Diagnostic Aids
Extremely low system voltage can cause this DTC to set falsely. Refer to Battery Charging.
Test Description
The number below refers to the step number on the diagnostic table
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 | |
Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the repair? | System OK | -- | |
