4WD will not engage, no message?

Tiny
1PASVANAS
  • MEMBER
  • 2005 GMC SIERRA
  • 6.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
Push the 4-wheel drive button to engage; it blinks like 5 times and stops blinking. Checked the PJ to the Transfer Case Shift Motor. There is ground at the center wire, and 5VDC at the orange wire. Wish I had a schematic for the system. A new transfer case shift motor gives the same result. What is pulling the 12VDC down to 5VDC?
Monday, March 23rd, 2026 AT 1:23 PM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 55,211 POSTS
The 4WD switch blinking about 5 times and then stopping usually means the TCCM tried to make the shift, did not see the expected feedback, and aborted the command. I have seen the front axle actuator go bad and cause this problem as well so you might want to remove it and then work the system to see if the actuator works. Also, there are three fuses that run the system so please make sure those are good as well. Here are the fuse and locations along with the system wiring diagrams so you can see how the system works. Check out the images (below). Please upload a short video in your response, so I can see what's going on.
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Tuesday, March 24th, 2026 AT 9:13 AM

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