Transfer control switch lights go on when initial start, then go out. No lights while truck is running. Cannot engage 4 wheel drive. Service 4 wheel drive light is on. Occassionally can get it to go in, but then can't get it back to 2 wheel. Turn off, restart in neutral can then get back into 4 x 4.
The 4X4 system is controlled by a electronic control module . Can set a number of DTC'S - diagnostic trouble code's . Having the vehicle check for DTC'S would be your best bet ! Not at autozone or advance or any parts stores . They can not pull these code's . Need a factory or professional scanner . Your best bet , take it to a qualified repair shop.
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.
sound like problems in transfer case shift module.
SOURCE: 1999 tahoe 4 wheel drive trouble light is on. Wont go into 4
On the full size, the front actuator is electric, not vacuum. So check the fuse.
When in 4wd mode, a switch on top of the transfer case conducts 12
volts out to the actuator. Wire #50 (brown) is the 12v feed, and it
conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the
front differential - it looks like a large bullet that threads into the
front diff.) If it has 12 volts, check the transfer case switch and the power
feed to the transfer case. I'll assume it is the actuator, if the plug to the actuator is not getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated
by voltage. When it heats, the pin in the end swells and pushes a shift
fork in the front differential. The shift fork engages a spline on the
passenger side of the differential, and boom! you have 4WD, with out the 12 volts you have 2WD.
GM offered an upgrade to this actuator that is a motor instead of a
heated device. However, it requires a small harness addition, a spacer,
and a new actuator. It is about a $150 to $200 option.
If I were you, I would buy a new heated actuator. They are available at
most auto parts stores, and are about $90. They are also on eBay for
about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.
Good luck, That actuator is usually the problem 90% of time but check the fuse to the 4X4.
SOURCE: My 1999 chevy silverado 1500 four wheel drive
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.
SOURCE: 1999 chevy silverado service 4 wheel drive light
I had a similar problem with
the Service 4 Wheel Drive light which came on intermittently then became more
consistent in the message center display. It would go into 4 wheel drive if the
message center did not display the Service 4 Wheel Drive message in the message
center, but not when the message was displayed. I found the transfer case
switch module in the dash was defective, and it has been working with no other
problems for three years.
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