Having trouble with your 4-wheel drive not operating or your 4-wheel indicator light flashing?

If you have a General Motors Pickup with a NV246 or NV263 transfer case, or a General Motors Sport Utility Vehicle with a NV126 or NV226 transfer case, the following Diagnostic Trouble Codes (DTCs) often occur. Any of these codes may be set in any combination: P0700, P0836, P0500, C0327, C0500, and C0500 in the different modules.  You may also notice a grinding noise or vibration from the front axle area of the vehicle.

The following are frequent trouble spots, so these connections should be checked: Transfer Case Control Module (TCCM) G110, Engine G103, G104 and G107 at the back of the engine, ground G201, part of splice pack SP201 and ground G102.

The problems may be caused by chafed TCCM wiring harness, especially at the park brake cable release spring area.

The TCCM will need to be replaced if Code C0500 is present.

Examine the pin tension and connector crimps at:

  • - the encoder motor (pins A, B, C, D, E, F, and G)
  • - TCCM connector C1 pins B2, A7
  • - connector C2, pins A8
  • - connector C3 pins A, B, C, D
  • - connector C151 pins A, F, G, E
  • - connector C154 pins A, B and C
  • - the under-hood relay center

Also these connections should be checked:

  • - TCCM G110
  • - TCCM engine G103
  • - G104 and G107 at the back of the engine
  • - ground G201 part of the splice pack SP201
  • - ground G102

If you get DCT CO327 only when you shift to four-wheel high, you may have a fluid contamination problem. Inspect the fluid, and if you find metal, you may need to replace the transfer case.

If the problem has been going on for a while, look at the front axle. Make sure the wiring is in good condition and connected, and check the shift sleeve teeth in the front axle assembly.

If the problem continues, a likely cause is an encoder sensor. Before removing the encoder motor assembly, make sure the unit has been shifted to the proper position, NV246 in neutral, NV263 in 2-wheel high. If the unit won’t shift, remove the transfer case fuse, generally marked TREC 30 AMP, located in the under-hood fuse block. After re-installing the fuse, the unit will usually shift, allowing you to attain the desired position.

Be sure to browse our shop for new, used, and remanufactured GMC transfer cases.