Is my 4WD working???

[dogfriend]

I took it to AutoZone and the diagnostic hookup found no error codes, not sure if the guy knew what he doing.

He would need to use a scan tool that can scan for GEM codes - if he only can scan the PCM, then it wouldn't give the codes. If you are getting flashing lights, it should set a GEM code

So I'm thinking that I should remove and clean the front and rear speed sensors. To make sure I am after the right thing, is this the rear sensor: Rear Sensor. And is this the shift motor that must be removed in order to access the front sensor (pointers to mounting bolts): Shift Motor

Unfortunately, the links that you gave don't work for me, but I think that if you trace the wires from the harness that plugs into the Transfer Case, you will be able to find the speed sensors easily.

Do I have to worry about any fluid draining out when I pull these items? Will I need to replace any seals? How exactly should I clean the sensors?

I believe that both speed sensors are above the fluid level, but I think that I drained the fluid out anyway. The speed sensors have an o-ring seal. You shouldn't need to replace them, but you might want to replace to avoid leaks later. The sensors have magnets in them, so you would clean them by wiping off any metal which may have collected on them.

A couple other things: I recently replaced the fluid in the transfer case, at this mileage I realize it was way overdue but the fluid was still pretty clean looking. Much cleaner than me after I got Dextron all over my shirt trying to refill the case anyway I have been guilty of NOT putting the vehicle in 4WD every month or so, could something be "stuck" somewhere? Also, I recently traced a problem with the defrost control to a broken vacuum line, are there any vacuum lines that (if they were leaking) could cause these 4WD symptoms?

Thanks very much,

russ

Your 96 has a vacuum disconnect for the front diff - it is possible that a vac leak could cause a problem with engagement of the front diff - I don't know if that would also cause the dash lights to flash.

 

[Stumpgrinder]

Hi and thanks for the replies!

I haven't had a chance yet to crawl back under the vehicle, but in the meantime here is a little more info:

1) Try this link to view the stuff I'm talking about: Sensor Pics

2) I'm pretty sure that the same thing happens if I select 4W Low, in that the lights still flash and go out.

3) If I go to Autozone again I'll make sure they can read GEM codes, I got the feeeling the last guy that did it wasn't very experienced. What do PCM and GEM stand for anyway?

4) As far as the vacuum leak idea, I'm pretty sure the front diff IS engaging, the problem is that the drivetrain is behaving as if it only goes into 4W Low.

Thanks again, and I will let you know what I find...

 

[dogfriend]

1. In your second pic, you can see that the fill port is under the rear speed sensor, so you shouldn't get any fluid draining if you remove it. I'm not sure about the front one under the shift motor.

2. The lights could be flashing for several reasons; it could be because the shift motor is not turning, not turning completely, or some other reason like the speed sensors are not working. Scanning the GEM is really the only way to know.

3. PCM stands for Powertrain Control Module - the computer that runs the fuel injection, determines auto trans shift points, runs OBD (Onboard Diagnostics) emission tests, ect. GEM stands for Generic Electronic Module (seriously ) - the computer that controls the intermittent wipers, the door locks, the courtesy lights ect. On the 4wd models, the GEM also controls the functioning of the Control Trac system.

The PCM is found under the hood, on the pass side firewall. The GEM is behind the dash, to the right and behind the radio.

The genius at Autozone will need a scan tool that can specifically scan for Ford GEM codes; he won't be able to do it with a generic scan tool unless its a very good one.

4. I don't think that a vacuum leak is causing your problem, but I mentioned it because you asked the question. I'm guessing that it could be a problem with the shift motor, but that is just a guess.

 

[Stumpgrinder]

Fixed!

OK I *FINALLY* got around to wrenching last weekend.

1) Remove harmonic balancer. (13mm)

2) Remove shift motor. (10mm X 4)

3) Remove front and rear output shaft speed sensors. (10 mm)

4) Separate electrical connector.

5) Use needle nose pliers and pull red retainer from shift motor side of electrical connector.

4) Use small screwdriver/knife to lift the locking tab under the brown wire pin. While lifting the tab pull brown wire out back of connector. You can now take the shift motor, speed sensors and wiring harness from under the vehicle.

5) Using same technique as in #4, release each wire to the old sensors and insert the new. I did one at a time to be sure I did not screw up.

6) Get back under vehicle and re-insert the brown wire.

7) Replace the red retainer.

8) Thread brown wire into the plastic shroud leading to the rear sensor.

9) Smear film of permatex on shift motor gasket surface.

10) Install front and rear speed sensors

11) Install shift motor.

12) Reconnect electrical connector

13) Reinstall harmonic balancer.



The entire job took maybe 30 minutes, and I went slowly to avoid mistakes.


End result: I now have fully functional control track 4WD!!!



A BIG THANK YOU to everyone on this forum who offered advice/help. You are a great crew!!!