4 Wheel Drive/SUVs: 4wd selector switch or tccm, light duty trucks, communication conditions

Question
QUESTION: i have a 2003 chewy S-10 4wd and the 4wd selector switch has been acting up every once in awhile and it will flash and sometimes would not go into 4wd.the other day i had it in 4wd and the selector switch lights went out and it is stuck in 4wd and i cant get it out.is there any way to get it out manually or not. i went to the junk yard and put a used tccm and selector switch in and nothing. i also checked the fuses that i thought could effect it and found nothing wrong. how can i check and see if im getting power to the tccm or if there is a broken ground somewhere.

ANSWER: Yukon,

It is possible that the used unit you purchased is faulty also.  I would purchase a repair manual and go through the testing procedure to confirm that this is the faulty component.

There is a service bulletin out on the TCCM:
Bulletin No.: 05-04-21-002

Date: March 10, 2005

INFORMATION
Subject:
Guidelines for Replacement of Transfer Case Control Module (TCCM)

Models:
2005 and Prior Light Duty Trucks

with New Venture Gear (NVG) Transfer Case (RPOs NP1, NP4, NP8)
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.

Parts reviewed at the Warranty Parts Center (WPC) have a 75% No Trouble Found (NTF) rate. The only two legitimate reasons to replace the TCCM are:
^    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.

No Communication
^    The no communication conditions referenced here are 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 tells the technician 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.

Diagnostic Aids
^    When diagnosing a transfer case electrical control system, ALWAYS check power and ground wiring first.

^    Test the connections for intermittent or poor connections, complete plug insertion, bent pins, pushed out terminals and water contamination.

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 shown.
^    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.

Carl


---------- FOLLOW-UP ----------

QUESTION: how do i clear the dtcs from the unit and how do i test it?

Answer
Yukon,

This is normally done with a scanner, or code reader.  There are several inexpensive ones on the market for personal use, or you can take it to a shop and have them run a diagnostics test on it and clear all old codes.

On some vehicles this can be done by disconnecting the battery for a period of time, usually a minimum of 30 minutes to overnight.

Carl