For 1990-2009 cars only
Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC C0550 37: Electronic Control Unit Malfunction Watchdog/Safety FailureDTC C0550 39: Electronic Control Unit Malfunction Internal Electronic Failure
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Watchdog/Safety Failure | Internal Electronic Failure |
|---|---|---|---|---|
Electronic Control Unit Malfunction | -- | -- | DTC C0550 39 | DTC C0550 39 |
Circuit/System Description
This DTC indicates and RAM/ROM checksum, a EEPROM failure, or an ECU malfunction due to an internal microprocessor failure.
Conditions for Running the DTC
| • | The ignition is ON. |
| • | System voltage is 10.5-18 volts. |
Conditions for Setting the DTC
The EEPROM, RAM and ROM, and ECM Microprocessor do self checks against one another and the data does not match causing the DTC to set.
Action Taken When the DTC Sets
| • | Shifting is still disabled until the DTC has cleared itself. |
| • | The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle. |
Conditions for Clearing the DTC
| • | The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present. |
| • | A history DTC clears after 40 consecutive warm up cycles without a fault present. |
| • | History DTCs can be cleared using a scan tool. |
Reference Information
Schematic Reference
Transfer Case Control Schematics
Connector End View Reference
Transfer Case Control Connector End Views
Electrical Information Reference
DTC Type Reference
Scan Tool Reference
Diagnostic Aids
It is sometimes possible to set this DTC falsely due to low voltage. Attempt to clear this DTC and retest.
Circuit/System Testing
- If this DTC sets attempt to clear the DTC and Retest.
- If the DTC is cleared, but then resets then replace the transfer case control module, program, and complete the transfer case motor learn procedure.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for TCSCM replacement, setup, and programming |
