4wd will not engage on 2002 gmc sierra 1500

Light on , DTC- diagnostic trouble code stored in the 4X4 control module . Take's a professional type scan tool to read these code's . Your best bet AAMCO . or dealer .

THE TRANSFER CASE MOTOR IS ONLY FOR 4WD LOW. That would have never been the problem as soon as you confirmed it shifted into 4wd Low. 2wd and 4 Hi work off of vacuum. You may have one or two issues. A vacuum leak up by the front axle that engages the 4wd HI or the sensors on the transfer case.

fullyjr.

Engaging from 2WD - 4HI/Lo requires movement of the vehicle. very low speed under 5mph, push button should engage. the vehicle has to be moving.

You probably have a bad encoder motor.It is located on the side of the transfer case on the drivers side.It is black.The other problem they had with these was the switch but you have already replaced this so your next thing is the encoder motor.Hope this helps.Good luck.

Is the motor and control board on the transfer case working sometimes it hangs up and tapping on it with a small hammer jars it loose.

see if the front driveline engages, then move to the front wheels if they do not engage check the actuator on the front diff

could be your front actuator or your actuator motor on the transfer case.

try reversing six to eight feet after shifting into 4WD. PLEASE RATE MY ANSWER.

while in drive, engage the 4wd, then shift into neutral for 2 or 3 seconds, then shift back into drive. it works for my '98 ram.