4wd engages but 4wd service light illuminates replaced dash switch and 4wd vacuum solenoid

Flashing super select 4wd lights most often occur when the front differential automatic disconnect is not engaging /dis-engaging when you select/deselect 4x4 drive. Causes are:

- front differential sensor switch is damaged or faulty
- actuator rod/shaft jammed / seized (perhaps sand/mud/dirt)
- vacuum lines leak/popped off fittings
- vacuum solenoid valves (2no.) either maybe faulty
- electrical wiring connection issue (ecu/solenoids/switch)
- combination of the above

Check the vacuum switch under the hood in the center of the firewall...follow vac diag

We may need more details. Does your 4wd dash light illuminate? Do you hear clicking from the dash? If it does not, you are dealing with a fuse or transfer case issue. If you see the light and hear clicking, it likely is not your transfer case but either your 4wd solenoids (attached photo) on the passenger side firewall or the actuator on the front differential. Pop the hood and listen for clicking from the solenoids, if the click, direct your attention to the actuator. It is vacuum actuated so it should move about an inch when engaging and disengaging 4wd. It sometimes gets stiff so see if you can move it by hand to free it up.

There are many vehicles which notice same issue with 4wd not engaging in low or high mode.I suggest you few help links related to these issue,with there troubleshooting details and solutions.
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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Service 4wd warning light on Dash? http://howtobyme.blogspot.com/2011/11/service-4wd-warning-light-on-dash.html

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Car automatically switches to 4wd low?

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These are the help links related to your issue.Going through these help links,will guide you to troubleshoot and solve the issue noticed on your car.
Keep updated for more help.
Thanks.

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 ( this is what you seem to have, the transfer case is engaged and will drive the front shaft mine was a key on engine off test ).

- 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.

-- 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.


Usually the case is cracked vacuum lines from the solenoids, the next common is a cracked vacuum reservoir box, and 1 time I have seen the mount for the vacuum disconnect motor broken ( motor floating free so it could not push against the axle )

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.

I am going to guess the drive shaft will not turn, and the problem is the shift disconnect motor on the front axle, or the shift solenoids.
The shift motor looks like this


The shift solenoids look like this :


You can check the shift solenoids with a vacuum gauge. The blue vacuum line is the 4WD operation, the pink is the 2WD operation. Pull the vacuum line at the shift disconnect motor, and install the vacuum gauge. Shift into 4WD and the vacuum should be on the line, and hold. If not could be the disconnect motor or the vacuum line to the motor.

Could also be the shift motor in the transfer case, but with the 4x4 light on the cluster lighting up, the transfer case should have shifted, the confirm comes from the transfer case to illuminate the 4x4 indicator on the cluster.

Sounds like the selinoid on the transfer case is not fully ingaged.....?

If its not engaging into 4 WD the vaccum actulator is more than likely stuck. The actulator is located on the front of the axle next to the the front gear hub it will have a plastic cover over it. Unbolt the two 10mm bolts that hold the cover on and spray down with WD-40, also pull back the rubber cover thats on the actulator staff and spray it. You might have to hit the staff a few times to get it to move just make sure its in 4WD. I had the same problem, that part is exposed to alot of water, snow, salt and so on. Or you could just replace it but its cheaper to spray it down with WD-40

Transfer case engages/disengages via a vacuum line. If the vacuum line is cracked, often by age and cold weather, it has to be replaced to allow a good vacuum pressure.

Check the super select solenoids. I had the same problem with my pajero/montero io, when I released 4WD from 4H to 2H the two front wheels lights started flashing. They stopped flashing and was solid on when I re-engaged the 4WD (2H to 4H).

My problem was a failure in the 2H solenoid, it was not producing enough vacuum. The problem was intermitent at the begining and then was permanent.

I checked the solenoids in this way:
1) The solenoid that receives the vacuum in the botton is for 2H
2) The solenoid that receives the vacuum in the top is for 4H
3) Both solenoids operate in the same way, they only change in the way they transfering vacuum from top/botton to the exit pipe (2H or 4H). The difference is that one has the vacuum input on the top and the another one in the botton.
4) The default position when you disconnect the electronics is 4WD
5) Try disconnecting the electronics and switching the output pipe between the solenoids. This will put the solenoids on 4WD position and you changed the pipes, so the 4WD should disengage.

4WD should disengage if your 4H solenoid is OK, the ligths should now flash when you change from 2H to 4H because 4WD cannot engage because the pipes are switched. You can also check the vacuum of each solenoid with your finger on each one.

If this doesn't work, try to bypass the solenoids and connect the input vacuum hose to the 2H output pipe. If the lights doesn't turn off in 2H mode it's posible that you have different problem.

Also check this address: http://4wd.blogeasy.com/article.view.run?articleID=318776

Good luck.