2003 GMC Sonoma 4 WD Not Working - Please Help ASAP

AUSTIN2863

MEMBER
2003 GMC SONOMA
6 CYL
4WD
AUTOMATIC
121,000 MILES

My 4wd will engage in 4Lo but my 4Hi will not engage. I can hear a click in the dash and at the transfer case while the 4Hi and 4Lo lights flash but then it lights 2HI back up and nothing else happens. I tried replacing the selector switch on the dash but the new one does the same thing. Also when you plug a diagnostic tool to the computer it states that there is "no communication" with the transfer case. I cannot afford to take it to the dealer, could you plaes help me?

Sunday, October 18th, 2009 AT 1:58 PM

1 Reply

BRIAN 1

MECHANIC
1,030 POSTS

Check the connector at the transfer case control module, its on the pass side kick panel. Usually you will find corrosion on the connector and tccm itself, from water leaking inside the vehicle, very common on these. Check that first and post back with what you find. Also you can manually get the codes without a scan tool, try this Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. Post the codes.

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Wednesday, October 21st, 2009 AT 8:48 PM