Drivetrain - TCCM Replacement Diagnostics/Guidelines

Information IB05-05-S007

Guidelines For Replacement Of Transfer Case Control Module
(TCCM)

ISSUE DATE: MAY 2005

Affected Vehicles

2003-2005 Isuzu Ascender (US/UT) with 4WD.

Service Information

Dealers are replacing the TCCM unnecessarily.

Dealers are replacing the TCCM with codes stored in HISTORY only. The TCCM does not have a current fault condition when tested. Properly diagnose and repair the transfer case control system prior to replacing the TCCM.

Important:
These are the only two legitimate reasons to replace the TCCM:

^ Diagnostic Trouble Code (DTC) C0550.

^ NO Communication with a scan tool.

DTC C0550

This DTC indicates that the module has an internal fault and should be replaced. Refer to DTC C0550 in the Service Manual for further information.

No Communication

^ The no communication conditions referenced here is also caused by a module internal fault to a point where the module physically will not talk. A technician cannot pull DTCs from the module because it will not communicate. The module is electrically dead.

^ No communication is not to be confused with a U1026 code. This code indicates that the module may still be functioning, but is temporarily off line. This code may be set by the Instrument Panel (IP) or the Powertrain Control Module (PCM) against the TCCM. The technician needs to figure out why the module went off line. These are typically caused by connection concerns. There is no need to replace a TCCM for a U1026 DTC. Refer to the Service Manual for further information.

Diagnostic Aids

^ When diagnosing a transfer case electrical control system, ALWAYS check the power and ground wire first. Refer to the Service Manual.

^ After repairs are complete, ALWAYS clear DTCs from the module prior to a system function test. If codes are not cleared first, the system will not function after repair. The technician may erroneously think that the system is still down and that further repairs are needed.





^ Test connections for intermittent or poor connections, complete plug insertion, bent pins, pushed out terminals and water contamination. Refer to Testing for Intermittent and Poor Connections in the Service Manual. Pay particular attention to the terminal connections at the module. Spread or open terminal connections may create an intermittent contact. Do a pin drag test. Refer to the terminal testing information in the table.

Terminal Testing tools and service terminals can be found in the Terminal Repair Kit J 38125 or ordered separately through Kent Moore 1-800-345-2233.





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