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Jettadan1, Chevy Technician
Category: Chevy
Satisfied Customers: 5064
Experience:  Most of our fleet is chevy.
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97 chevy blazer: has electronic 4wd..It wont shift..front wheels

Customer Question

My 97 Chev Blazer has electronic 4wd. It wont shift into 4hi, and when I shift into 4lo, I feel the t-case shift but the front wheels get no power. can this be fixed easily and cheaply by myself. I am very mechanically inclined.
Submitted: 7 years ago.
Category: Chevy
Expert:  Jettadan1 replied 7 years ago.

Bulletin No.: 05-04-21-002

Date: March 10, 2005


Guidelines for Replacement of Transfer Case Control Module (TCCM)


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.



Dealers who unnecessarily replace the TCCM that are found to have No Trouble Found (NTF) at the WPC will be returned to the AVM (Area Service Manager), or the DSM (District Service Manager) in Canada, through the Regional Feedback Process and may be charged back for the repair through the WINS system.







What this means is usually there is a fualt with the wiring or connections to and from transfer case. And you have fuses that could have blown

Expert:  Jettadan1 replied 7 years ago.
I am a chevy expert as well as a car expert and I have moved our question to chevy.
Customer: replied 7 years ago.
my scan tool is showing no codes for the 4wd, and I have replaced the fuse. the dash lights come on for BOTH 4hi and 4lo when shifted into 4lo. the lights flash and then go back to 2hi when 4hi is selected.
Expert:  Jettadan1 replied 7 years ago.
Have you gotten under vehical to check connections. All connections need to be followed to and from tranfer case. If you look good on the connection


  1. Lower instrument panel trim.
  2. Two screws securing the transfer case control module to the bracket.
  3. Electrical connector from the transfer case control module.


  1. Electrical connector to the transfer case control module.
  2. Two screws securing the transfer case control module to the bracket.
    • Tighten transfer case control module screws to 8 Nm (71 inch lbs.).
  1. Lower instrument panel trim.
s and they are clean then the control module may need to be replaced.



Customer: replied 7 years ago.
I can accually feel the transfer case engage in 4lo but there's still no power to front end, but it wont shift into 4hi
Expert:  Jettadan1 replied 7 years ago.

When that happened t me in my 4x4 it was just a vacum hose that came off. It was mounted by the front cross memeber. I am not sure if your electonic system involves vacum but you may want to try. There is an actuator switch down there also that could be the root cause. It going into low gear is different that shifting intoXXXXX