4WD DRIVE LIGHT IS ON, BUT 4 WHEEL WILL NOT ENGAGE

The reason the light is flashing constantly is because the vehicle is sensing that four wheel drive(4WD) is not working. These 4WD systems use vacuum from the engine to engage/disengage to front axle. The vehicle probably has no vacuum going to the front axle, which would not allow the 4WD shift to complete, which would then leave the light on the dash flashing.
First thing to check is that the vacuum actuator on the firewall is working as it should.

no year car.
no model jeep stated.
now 4wd option stated (
command trac, Select track. quadra-trac/drive?,)
or if unknown what transfer case is there (tag on rear says)

the front axle have the vacuum valve on it.
does it work, the vacuum servo ( test it?)
if no vac. servo there, that is the newer jeeps.

is this your jeep?

There may be vacuum lines running down to the hubs. If so check them for vacuum when engaging and dis-engaging 4 wheel. If you can't feel any vacuum, trace lines, and check for leaks.

Hi, depending on the vehicle, there can be different controls. Standard control, 4hi, use in slippery conditions, never on dry pavement. Just push the button, and it will engage. 4low is for extreme conditons and the transmission must be in neuteral to engage 4lo. If you have auto 4wd button, just press the button in slippery conditions. If you have a denali, it is all wheel drive, and there are no buttons to push. So, depending on the model, there are multiple ways, but pushing the button engages it. Good luck...Goop

what's wrong with 4wheel drive when light blinks on 4hi other than not engaging

fullyjr.

Engaging from 2WD - 4HI/Lo requires movement of the vehicle. very low speed under 5mph, push button should engage. the vehicle has to be moving.

your doing it right but your accuater is bad 59.00 auto zone easy install

if it is a lever type and not automatic 4WD. You have to manually get down and turn the hubs clockwise to engage or couter clockwise to remove from 4WD. then Push the lever to 4L or 4Hi. If it is automatic. You press a button to engage 4wd.

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

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.