Question about GMC Sierra
Four wheel drive will not engage when switch is turned to 4x4
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Posted on Jan 02, 2017
SOURCE: four wheel drive wont engage
If you have push button 4-Wheel Drive, it is recommended that you use it every once in a while, in order to keep gunk, rust, and corrosion to build up on moving parts. The mostly likeley (though not definite) reason would be that you let the 4-wheel drive unused for so long that corrosion has built up on the parts and the actuator that engages the 4-Wheel Drive doesn't have the power to engage it past the corrosion.
You'll need to take it in to be cleaned, or to have parts replaced. In the future, every month or so, engage 4-Wheel Drive and drive around in some mud, grass, sand, or any other loose ground for a bit, just to keep the parts moving and clean.
The service Four wheel drive light is to alert the operator the system is not being read properly by the ECU.
If the ECU loses contact with or position of the Transfer case actuator motor the service light will come on. Same thing goes for the front diff actuator.
So it may be a bad switch, sensor, or an actual problem in the 4WD linkage. This is not a Oil Change light that you can ignore a few extra weeks - it indicates a problem that should be taken care of ASAP to avoid costlier problems down the road.
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Posted on Feb 21, 2009
I have a 1994 ford f150, my 4 wheel drive keeps trying to engage by itself even without me touching the automatic hub button....at time you can even hear it engaging and disengaging by itself, the low range light even comes on (dimly)...what could be the cause? the transfer case motor looks good and so does the wiring.
Posted on Nov 24, 2009
Operationally vacuum holds the IWE ( Integrated Wheel Ends ) out, and once vac is removed the spring engages the IWE.
Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
If it turns it is a problem with the transfer case.
If it doesn't it is a front axle engagement problem.
- If the front drive shaft does not turn :
Shut of the truck ( still jacked up, and supported ) remove the vac lines from the IWE. The spring should push the gears in, without the vac line on.
Check the vent line ( tube that is routed into the engine compartment with nothing attached to it ), for blockages.
If the vent line is clear, and with the vac lines off the IWE should be engaged ( both front wheels locked ).
If they lock, the problem is with the IWE solenoid not shutting off vacuum to the IWEs. There is a TSB on the 2004-2006 IWE solenoids, a newer revision has been made, and used from 2007 and newer MYs.
Here is a block diagram of the IWE system
Posted on Dec 20, 2009
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.
Posted on Dec 28, 2009
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