I have a 2003 chevrolet tahoe 5.3 in I had the truck in two wheel drive so go put it 4 wheel drive in think a light come on say sevice 4wd what does at mean

SOURCE: heater core on a 2003 Chevrolet pickup 4 wheel drive crew cab

if you have air conditioning you will need to take it to a garage and recover the r134, you will need to remove the dash to allow you to remove the heater box, it's an ugly job, I've done a dozen or so and can do it in about 6 hours now, the first time it was closer to 11 hrs, good luck

SOURCE: 03 Chevy Tahoe Z71 - 4wd not functioning

my son has one and his did that and it was a fuse he put a new one in and it is working good now

SOURCE: 2003 chevy tahoe service 4 wheel drive on

I had this light come on in my 2003 tahoe it ended up to be the transfer case motor (encoder motor) was bad. I got one out of a used part store and the light went off right away.

SOURCE: 2004 Ford F-150 extended cab FX4. 4WD problem

Your front hubs are automatic locking hubs, and the gears are hard nylon. These hubs break very easily, therefore causing you to lose your front wheel drive in 4 high, or 4 low. If you replace the hubs with "WARN (name brand) " manual locking hubs, you will never have the issue again. Of course, you will have to get out of the truck and manually lock the hubs, but they are metal gears, and much more durable. I've personally seen the issue several times, and changing the hubs has resolved the issue every time.

SOURCE: Chevrolet Suburban 4 Wheel Drive Indicator Lights

Just serviced my own 4x4 Suburban, by buying a 2nd hand encoder motor and replaced the old one, which was trashed by the winter salt. The device is prone to failure since it's made of alluminium and water has an easy time of entering the unit and trashing it.

CAUTION: Abbreviated gratuitous information of how an encoder motor was serviced. If unqualified to deal with repair, seek professional service.
CAUTION: Read at one's own risk.

To replace it, you need to crawl under the vehicle and remove the front drive shaft;

Disconnect the electric harness to the encoder motor, followed by unbolting it.

Take replacement encoder motor and install. There may be an issue with aligning the cogged cam of the transfer case to the encoder motor. If so, the vehicle's 4 wheels will need to be raised off the ground. The engine started, transmission in Park, and using a Vice-Grip® wrench gently rotate cam clockwise approximately 1/16 to 1/8 of an inch, then while set in this position, stop engine. Now attempt to align and attach the encoder motor.

After successfully attaching new encoder motor, attach its wiring loom.
Test vehicle.