The 4WD transfer case encoder motor position sensor or the selector switch may fail causing the service 4WD message to be displayed. Fault code(s) stored in the transfer case control module will be of assistance in determining the exact fault causing the message to be displayed.
Service 4WD Message May be Displayed on Chevrolet Silverado 1500 HD
Average mileage: 143,540 (64,500–211,100)
Drive Train affected: 4WD
18 people reported this problem
2003 Chevrolet Silverado 1500 HD - 4WD 118,345 mi, Visitor
selector switch not working no lights,got a new one same thing no lights,service 4wd still on dash ,4 wd not working at all
Service 4WD message come on and the transmittion will not switch from 2WD to 4WD or 4WDL. Turning the truck off for a short period of time and restarting the truck will reset the system. The 4WD switch will work properly for a short period of time. The meesage will reappear and the system will lock up again.
I have replaced the encoder motor twice and the shift control buttons on the dash and the SERIVCE 4WD light continues to come on when the truck is cold. In the summertime the message doesn't appear. In the winter, after the truck is warmed up, the 4WD works fine.
2003 Chevrolet Silverado 1500 HD - 4WD 93,000 mi, Visitor
DIC intermittently displays SERVICE 4WD Dealer states encoder sensor electrical failure. Suspect internal encoder sensor issue. No noticeable problems shifting in and out of 4wd. Not yet fixed. Is a reprogramming necessary for this repair?
2003 Chevrolet Silverado 1500 HD - 4WD 193,000 mi, Visitor
I have had the problem with the 4wd train two times. I have replaced the 800.00 part twice and am now having the same problem for the third time. What are you going to do to correct this problem that I continue to experience.
2003 Chevrolet Silverado 1500 HD - 4WD 103,000 mi, Visitor
Servers 4 WD light come on.it is not fixed.
2006 Chevrolet Silverado 1500 HD - 4WD 211,100 mi, Visitor
code is co327 is this the sensor for trans case