BW 4493/4494 - Transfer Case

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

This is an internal fault detection of the transfer case shift control module (TCCM). This fault is handled inside the TCCM and no external circuits are involved.

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

Conditions for Running the DTC

* Ignition ON.
* System voltage 9-18 V.

Conditions for Setting the DTC

* The random access memory (RAM) of the TCCM has failed an operational test indicating that some portions of RAM are not functional.
* The read only memory (ROM) or the masked ROM of the TCCM has failed the Checksum test indicating that the data is not currently valid.
* The critical operational parameters stored in the EEPROM of the TCCM have failed the Checksum test indicating invalid data.

Action Taken When the DTC Sets

* The SERVICE 4WD indicator will be latched on and the system will be disabled.
* The transfer case control switch will display the current position LED while DTC C0550 is current, but further shifting will be disabled.

Conditions for Clearing the DTC

* Replace the transfer case shift control module.
* Perform the Diagnostic System Check - Vehicle.

Diagnostic Aids

* DTC P0550 detects the wrong copy of non-volatile memory in RAM or a RAM read/write failure.
* DTC P0550 detects a non-volatile memory write error.
* DTC P0550 detects a corruption of the EPROM/Flash memory.
* When attempting to set TCCM internal DTCs, let the engine run for at least 1 minute and then shut the engine OFF for 30 seconds. Following this procedure will allow for a complete TCCM shutdown. Reprogram the TCCM and retest the DTC to see if the DTC resets.
* A low voltage condition can sometimes falsely set this DTC. Attempt to clear this DTC and retest.

Reference Information
Schematic Reference

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

Component Connector End Views (Connector End Views By Name)
Description and Operation

Transfer Case Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

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

Circuit/System Verification

1. Engine running. Let the engine run for at least 1 minute.
2. Ignition OFF for at least 30 seconds to allow for the complete shutdown of the TCCM.
3. Ignition ON, verify that DTC C0550 is not set.

• If DTC C0550 sets, reprogram the TCCM. If the DTC resets, replace the TCCM.

Repair Instructions

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