Transfer Case - NVG 126-NP4

DTC C0550

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC C0550
- ECU Malfunction

Circuit/System Description

At each power-up, the transfer case shift control module runs a self-test on the following:

* EEPROM Checksum
* ROM Checksum
* RAM Checksum
* RAM Malfunction

Conditions for Running the DTC

* The ignition is ON.
* 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* Masked ROM code has failed Checksum test indicating that masked ROM data is no longer valid.
* ROM code has failed Checksum test indicating that ROM data is no longer valid.
* One or more ROM locations have failed operational test indicating that some portions of RAM are not functional.

Action Taken When the DTC Sets

* The SERVICE AWD 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 (Diagnostic System Check - Vehicle).

Reference Information
Schematic Reference

Transfer Case Control Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Transfer Case Description and Operation (NVG 126-NP4 - Transfer Case)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.