Service 4wd light only comes on when driving in 2 hi. If it is in auto or 4 hi it is fine. Is this the sensor unit?

The Internet, though, has a large number of web sites
where you can buy service manuals and schematics
from bookstores, publishers, and other collectors.
Here is just a sampling of what sites are out there:

Factory Auto manuals
http://www.factoryautomanuals.com/
search for : factory service auto repair manuals

Repair Service Manuals
http://www.repairservicemanuals.com/
the largest collection of Automotive Repair Service
Manuals and Owners Guides on the internet. Our
database currently holds over 54,000 entries
dating back from 1940 to more recent 2011.

about Chilton Repair Manuals
http://www.chilton.cengage.com/

about Haynes Repair Manuals
Haynes Publishing
Haynes auto manuals
http://www.haynes.com/

Hummer 4wd service light reset Questions & Answers - Fixya

www.fixya.com > Forum > Tags > 4wd service light reset
Hummer h2 2003 55000 mill ... service 4wd the liht is on all time Remote the battery wire from the car for 20 ... My 2006 H3 will not come out of 4 wheel drive?

Its your control module for the 4 WD on the transfer case hanging. They go bad often. I would replace

On these issue, there are few solved help links for troubleshooting the issue easily.-------

Click the link below: ---

No 4x4 light on dash?

http://repairhelpcenter.blogspot.com/2011/12/no-4x4-light-on-dash.html

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4X4 Truck makes roaring noise in the front end?

http://schematicsdiagram.blogspot.com/2012/01/4x4-truck-makes-roaring-noise-in-front.html

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Car will not go into 4WD high or 4WD low?

http://schematicsdiagram.blogspot.com/2011/12/car-will-not-go-into-4wd-high-or-4wd.html

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No 4x4 light on dash?

http://repairhelpcenter.blogspot.com/2011/12/no-4x4-light-on-dash.html

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4 wheel drive system will not disengage?

http://technoanswers.blogspot.com/2012/01/4-wheel-drive-system-will-not-disengage.html

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4WD light is flashing and beeping? NO 4WD high?

http://schematicsdiagram.blogspot.in/2012/02/4wd-light-is-flashing-and-beeping-no.html

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2002 Jeep Wrangler: 4WD Idiot Light is ON?

http://technoanswers.blogspot.in/2012/06/2002-jeep-wrangler-4wd-idiot-light-is.html

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Traction control switch will not engage on 4WD High or Low

http://whoisbyme.blogspot.com/2012/10/traction-control-switch-will-not-engage.html

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4WD light flashing and 4WD will engage after few minutes

http://repairhelpcenter.blogspot.com/2012/10/4wd-light-flashing-and-4wd-will-engage.html

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2008 Toyota Tundra: 4x4 Wheel Drive Light is Flashing?

http://technoanswers.blogspot.in/2012/05/2008-toyota-tundra-4x4-wheel-drive.html

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4x4 front differential will not engage the axle on ford?

http://technoanswers.blogspot.in/2012/02/4x4-front-differential-will-not-engage.html

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4x4 will not engage on Ford F150?

http://technoanswers.blogspot.in/2012/02/4x4-will-not-engage-on-ford-f150.html

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Dodge Ram 4x4 light keeps flashing

4X4 LOW LIGHT IS FLASHING ON DASH

http://technoanswers.blogspot.in/2012/09/dodge-ram-4x4-light-keeps-flashing.html

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Ford 4x4 front wheels will not engage?

http://technoanswers.blogspot.in/2012/02/ford-4x4-front-wheels-will-not-engage.html

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These details will help.

Thanks.

Well it could be the selector switch, but I doubt it.
Generally, the service light means something is not working that the computer controls. Solenoids and valves are a couple of possibilities.
The transfer case is shifted by solenoids commanded by the body computer based on the switch position on the dash.
You should be able to have a shop scan the body computer for trouble codes and proceed from there.
A basic code reader may not access the body computer.

2001 Chevy Blazer it likes to stay in 4 low. replaced sensor, pannel motor, older computern to check it was placed for a couple weeks or less it will do the same thing again. Just dies and quits has to be restarted agin still in 4 low . Tried to shift the gears slowly, Place in reverse and 2HD pressed and held while backing up this dinn't work either. To get it home I had to hold it in neutral and run the gears again ginally I got it to a shop. He is out of ideas too.

check switch connections,fluid level and actuator at transfer case if good have truck scanned for possible trouble code possibleas sensor or component going bad , some auto stores such as auto zone /advanced auto do it for free if theres a trouble code it will be a starting point

sound like problems in transfer case shift module.

Does the 4-wheel drive work ? Most of the time, it is a reminder to have your fluid changed. Other times, it could be a vacuum leak in the line that engages the 4-wheel drive. Check both of those first.

pull atc 25 amp fuse in underhood fuse center and 10 amp 4wd fuse inside cars fuse box,your problem is in control box behind kick panel on pass. side ,corrosion build up,