Front drive won't engage; 25A 4WD fuse blows.

The actuator will not be on the front differential or drive line, it will be on the transfer case, which is mounted behind the transmission. Follow the front drive shaft back from the front differential, and the component at the rear of the driveshaft is the transfer case. That is where four wheel drive is engaged/disengaged.
I'm not familiar with your vehicle, but if you have a separate lever to engage 4wd, there will not be a fuse for the actuator - it is a manual system. If the 4wd is selected electrically, check that all wiring and connectors on the transfer case are in good condition.

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.

Check the 4x4 wiring ground (directly behind the left front tire, mounted to the body). If the front axle actuator is still good, this is usually the source of frustration. Put some RTV Gasket sealer on the nut and bolt after you replace them to help keep it from corroding as fast.

Power as in 12 V DC ? if yes, you are not in the correct area, the front axle is locked in and out of 4x4 mode with vacuum.

Operationally vacuum shifts the front axle between 2WD and 4WD mode. The GEM ( Generic Electronics Module ) applies ground to the solenoid needed for the mode selected on the switch ( for ESOF ) or when the transfer case shift lever is moved ( MSOF ).The contact plates in the transfer case signal the GEM that the transfer case is engaged, and the Vacuum solenoids need to be activated ( either 2WD to 4WD or 4WD to 2WD ).


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 :
•With the truck running ( with front wheel back on the ground ), switch from 2WD to 4WD and back again, the vacuum shift motor should move the lever on the front axle.

Item #10 in this diagram

-- If the vacuum shift motor does not move:
1.Check for vacuum on the lines while shifting between modes. Pink vacuum line is 2WD mode, Light Blue vacuum line is 4WD.
2.Check the fuses for the 4WD system and the solenoids.
3.Check the vacuum lines from the vacuum shift motor to the solenoids on the firewall.
4.Check the vacuum lines from the solenoids to the vacuum reservoir box behind the battery.
5.Check the vacuum reservoir box for cracks.
6.Typical solution is the vacuum lines ( to the solenoids or to the vacuum shift motor ) are cracked or the vacuum shift motor has a cracked diaphragm and has water in it.
7.Could be the shift plate contacts in the transfer case are corroded / not making good contact, and not activating the solenoids.


- If the front drive shaft turns:
For ESOF system
-- Check the fuses for the transfer case, engine compartment fuse panel, 17 & Cab fuse panel fuses 13 and 23 ( verify with owners manual, 97-97 & 99-03 MY can be slightly different on some items ).
-- Try hitting the transfer case with a dead blow hammer ( do not use a metal hammer, it can damage the transfer case ) to see if the transfer case shift motor is hung up .
-- Check the transfer case connector, to make sure the connector pins are clean and making good contact.
For MSOF systems
-- Check that the shift linkage on the transfer case is moving when the lever is moved from 2W to 4H and 4L.

It does not matter the color of the fuse as long as it is a 25 amp fuse. I would suspect the wiper motor is defective.

i've been told it was the 4wd actuator located on the passenger side near were the cv joint goes in to the front axle a good test is to floor jack it up so both wheels are off the ground and have someone on the other side , put in nutrual turn both wheels one way at same time and the 4wd drive shaft should turn if not its your actuator, costs about $86 for anew actuator and takes about 5 mins to change once you have the tire off

There are 2 switches (one on top of the transfer case left side above shifter) this then sends power to the electric actuator to engage the front axle. Quite often the actuator is internally shorted causing fuse to blow. I'm sorry I don't have a schematic in front of me. The second switch is on the front axle and will illuminate the 4wd light when engaged. It could be shorted but won't inhibit 4wd operation (its a separate circuit). Remove the connector at the front axle actuator and jumper it directly to battery (using a fused jumper). if it operates, and fuse doesn't blow, then you have a wire chaffed to ground. Most often its near the front axle harness that gets rubbed thru. If the fused jumper blows then obviously the actuator is no good. I hope this helps some.

Operationally vacuum shifts the front axle between 2WD and 4WD mode. The GEM ( Generic Electronics Module ) applies ground to the solenoid needed for the mode selected on the switch ( for ESOF ) or when the transfer case shift lever is moved ( MSOF ).The contact plates in the transfer case signal the GEM that the transfer case is engaged, and the Vacuum solenoids need to be activated ( either 2WD to 4WD or 4WD to 2WD ).


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 :
•With the truck running ( with front wheel back on the ground ), switch from 2WD to 4WD and back again, the vacuum shift motor should move the lever on the front axle.
{ picture of shift motor }
-- If the vacuum shift motor does not move:
•Check for vacuum on the lines while shifting between modes. Pink vacuum line is 2WD mode, Light Blue vacuum line is 4WD.
•Check the fuses for the 4WD system and the solenoids.
•Check the vacuum lines from the vacuum shift motor to the solenoids on the firewall.
•Check the vacuum lines from the solenoids to the vacuum reservoir box behind the battery.
•Check the vacuum reservoir box for cracks.
•Typical solution is the vacuum lines ( to the solenoids or to the vacuum shift motor ) are cracked or the vacuum shift motor has a cracked diaphragm and has water in it.
•Could be the shift plate contacts in the transfer case are corroded / not making good contact, and not activating the solenoids.


- If the front drive shaft turns:
•For ESOF system
-- Check the fuses for the transfer case, engine compartment fuse panel, 17 & Cab fuse panel fuses 13 and 23 ( verify with owners manual, 97-97 & 99-03 MY can be slightly different on some items ).
-- Try hitting the transfer case with a dead blow hammer ( do not use a metal hammer, it can damage the transfer case ) to see if the transfer case shift motor is hung up .
-- Check the transfer case connector, to make sure the connector pins are clean and making good contact.
•For MSOF systems
-- Check that the shift linkage on the transfer case is moving when the lever is moved from 2W to 4H and 4L.

There is an electric actuator on the front axle that engages 4WD. This part commonly fails resulting in no 4WD. Unhook the electrical connector to this part and see if heater still blows fuses. If It does not blow the fuse, the problem is in the actuator. If it still blows the fuse then it could be in the wiring. Buy a repair manual and trace the wiring schematics.

Hello;
Sounds like yoou have a short either in the switch pod or in the 4wd electrics. Check for pinched wires or bare wires grounding out at the front axle and at the transfer case.
Thanks;
Rich
RPM Northwest