Pushbutton 4wd issue, 1996 F-150.

I have a 1996 F-150 4wd, E4OD trans, pushbutton 4wd control. It used to have auto hublocks, too, but they were replaced with manuals under warranty. 

Today, when I engaged the 4wd, the lights on the dash (one dot by the button, and one that says "4X4" in the dash) didn't light. The system would engage and disengage the front end, but not select low range, because it didn't realize that it had successfully made it to 4wd. 

Thoughts?

There is a sensor in the transfer case that senses when the shift shaft reaches the position where it is in 4x4.  It does this so that it actually knows it is physically engaged as opposed to just a dummy light that comes on because you pressed the button.  As far as I know, the system uses the same signal as the dash light to let it know it is ready to engage low.

My guess is that this sensor is not functioning.  Wire loose?  Bad sensor?

But despite the light not being on, you are successfully engaging 4hi?  You're getting torque to the front wheels?  It just won't go the 4lo because it doesn't know it can?

Does it matter that the hubs are now manual and they need to be locked prior to engaging 4-low?

No.  The automatic hubs he replaced are passive.  They use a little worm gear to engage the hub when they receive torque, then disengage when you take it out of 4x4 and drive in reverse for 10'.  The computer has no idea what goes on in the hubs.

The factory automatic hubs are plastic junk and break frequently.  I replaced my autos with manuals and don't have an issue.

In fact, I use 4lo in my truck for backing trailers.  The reverse gear in the 5 speed manuals is pretty high, so using 4lo wasn't a problem for me after I put manual hubs on regardless of locked hubs or unlocked.

The system is pretty simple.  It uses that sensor in the t-case to let it know that 4x4 is engaged.  His (for some reason) isn't signaling that it is in 4wd (that it's OK to continue to low range).  It thinks he's not in 4x4, hence why I thought maybe it was an issue with that sensor or the wiring.

Here is a picture.  Inside that round shifter housing is a rotary position switch.  It runs the servo motor until the shifter has reached the position where 4x4 is engaged.  Once it reaches that point, it will allow you to press the 4lo button and let the shifter continue to engage low range.

There is a 4x4 control module under the dash.  Some people claim it is a trouble spot, but I never had them fail.  I have had a couple position sensors fail.

Here is a good writeup on rebuilding the whole thing and it shows the rotary position sensor

Thanks, Curtis. 

It does actually engage and disengage the front axle as it should, so the problem is probably in the sensor/wiring.

I also do the "2lo" thing for backing trailers.  It keeps the trans from puking fluid when trying to exactly place a trailer on an uphill grade. 

Wait, are there two sensors?  It would appear that the one that runs the motor actually works, and the one that tells the 4x4 light to come on doesn't. This would probably be the same on non-pushbutton trucks, because my lever-shifted 4x4 had indicators on the dash for 4x4 and Low Range. 

As far as I know, it's just one sensor, but it may have two circuits in it; one for the light and one for the control unit.  The common problem is that the little plastic button that engages the switch gets a flat spot or just falls apart entirely.  My guess is that your sensor is either corroded or the button isn't engaging the switch to tell it you're in 4wd.  Depending on what the circuit is telling the controller, it might still engage and disengage 4x4 but won't go any further because it doesn't get the right info.  The sensor actually has several positions, not just three.  There are a couple triggers on the way to 4x4 and also on the way to 4lo.  So its possible that it is getting all the right triggers on the way to 4x4, but not the one that actually says it has arrived.

Many times people replace the whole motor actuator assembly when it could just be a switch rebuild or cleaning.  The switch is a common reason for the failures and the motor getting "stuck" because the sensor isn't giving the correct information to the control unit.

Totally unhelpful comment:  One of the things I like best about my low option Silverado is the shiny steel bar sticking through the floor that goes to the transfer case.

Streetwiseguy said:

Totally unhelpful comment:  One of the things I like best about my low option Silverado is the shiny steel bar sticking through the floor that goes to the transfer case.

Truth.  If my Branger gives me any more fits, I'm retrofitting a manual T-case.

Update: I got under the truck today and looked at some stuff. I unplugged and re-plugged the 10-pin connector that runs the motor, the sensors, and probably the VSS, which is under a shield that is also the slip yoke housing for the t-case. 

After doing that, I layed down under the truck and had my buddy push buttons (with the trans in neutral).

Here are the results:

Press 4x4 once. Motor runs, front drive shaft engages. No lights on the dash. 

Press LOW RANGE once. Motor runs. The dot next to the LOW RANGE button lights up, and "LOW RANGE" lights up on the instrument cluster.  

Press LOW RANGE again. Motor runs, lights go out on dash. 

Press 4x4 again. Motor runs, front drive shaft disengages. 

That sounds like a fried bulb in the dash to me.  It is actually engaging the low range?

I tried to think that the bulb was blown, too, bit there are two separate locations that should light up. 

And yes, low range works (and some lights on the dash work with it).