Ford 4WD doesn’t work, an interesting design and food for thought

My wife’s 1991 Ford explorer is approaching  21 years old, and has been a most trouble free car.

A recent conversation about early snow, maybe even down low caused my wife to mention that button on the dash that says 4WD doesn’t work.

It hasn’t worked for a long while, and since the computer manages it, I hesitated to look into it earlier, funner stuff to do in the shop 🙂

One thing you need learn is to spend the majority of your time learning how something  works BEFORE you attempt to fix it.  This vehicle is NEVER in 4WD, so the parts that activate the 4WDH and 4WDL and back to 2H are not likely worn out..

Using google I entered “91 Ford explorer 4WD doesn’t work”.. I followed the links and quickly found a forum discussion and learned that Ford used this same system in light Ford Pickups as well.

I read thru a number of posts and found out the Service Manual was $80. I gleaned what I could from the posts and picked a most probable cause.  What I learned from the posts is this system has what old computer geeks might call a code wheel, others would call it a position sensor, but whatever the case, part of the periphery has to be convinced it knows which of the three positions the transfer case is in.. 2H, 4WH, 4WL. Unless the system has a valid position, it will totally ignore your request. My symptoms, reported fixs all suggest a dirty or broken position sensor, or a bad wire or dirty connector to the sensor.

In a newer system, we could generate an error code, and store it to be read. If we were to look up such an error, it might say.. 4WD requested, current position unknown! but hey, this was the 90s, not so advanced yet 🙂

Motor and Position Sensor

Motor and Position Sensor


Here’s a picture of the rear of the transfer case, put a floor jack on the frame rail, driver side, and jack both tires off the ground.. add some jack stands for safety to get under here to look around. There’s a round harmonic balancer mounted back here with four bolts, 1/2 inch, remove same to improve the view.

Red  Arrow on left is the Selector Motor, next arrow is the position sensor. There’s three security screws you need to remove, (harbor freight has the bits cheap if you don’t). make sure you make a mark on case, and case lid before you pull screws and cover so you know where to put it back.

I removed this cover and found wipers, and a wheel and traces. I used 600 grid paper to lightly wiped down the wheel and very lightly over the fingers,and then followed up with a lot of scrubbing down with new paper towel, then blew it down with air to get rid of any lint.

I slapped it all back together, and it works perfect. Why did I post this? Because I same as earned $500 or more this morning, I bet if I had taken it to the Dealer, it would have been more. The forum mentioned the New Ford motor sensor assembly is $525.00, I wouldn’t put it past my local dealer to sell me one. A penny saved, is a penny earned, and Isn’t that why we’re DIYs?


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11 Responses to Ford 4WD doesn’t work, an interesting design and food for thought

  1. Michael La says:

    Nice write up George. I too steer clear of the stealership. I have not taking a car for service in many,many years. I do all my own repairs.

    It also reminds me of my own 4×4 troubles on my 1996 s10 chevy.
    ( Ford=Found On Road Dead) LOL

    Anyway I believe the Fords are similar in the mechanicals. First off the two differences with the button actuated 4 wheel and the actual shifter on the floor of couse is mechanical vs electrical engagement. I will only buy 4wheel vehicles with shift on the fly. The reasons are one less device to go wrong, and for towing behing a RV the floor shifters allows you to put the case in neutral. The buttons on the dash dont allow this.

    The button applications actually activate a motor that moves the case to the proper position. Aside from this there is also some type of vacuum actuator that pulls a fork in the front differential. Once the case hase moved to the proper position a vacuum switch at the case switches vacuum the this device. Mine and many are under the battery tray. This in turn pulls a cable going to the front diff to lock it in.

    In my situation I could not engage 4 wheel, or it would not disengage. I found all the vacuum lines coming off the manifould, brake booster, emmisions canister under the hood were dry rotted. After a internet seach on the situation and a haynes manual, I easily replace what hoses I needed, plus a failed transfer case switch. Total cost about $20 and my time. Could you imagine what the stealership would charge?????

    The actuators under the battery tray are the most common to go because its just a diaphram actuator. batterys that are not maintained well often leak acid on these and compromise the diaphram and or vacuum hoses. Also the cable going to the diff are know to break and or get bound up by lack of lubrication. Like the throttle on a motorcycle.

    So I hope this comment helps you and others if further issues arise with 4 wheel drive mechanics.

    It is all so simple, and once you understand the series of events and parts involved to activate your 4 wheel drive its easily repairable with patience and basic common sense.

    My motto is take the time to find out how it works and why, and you can repair anything. This will enhance the path you take during troubeshhoting.

    OK I will stop rambing.

    Have a great day,

    Your friend from NJ

    Mike L.

    • George B. says:

      Mike well put…Maybe I need remind folks of the differences in systems, I think my Ford uses the torque seen on the front drive shaft to engage the hubs automatically..(on the fly). No cables, no vacuum required. I was a Chevy man for years, but who can argue with 260,000 miles of service over 21 years with zero major repairs! but we need know the history of this engine, it was first used in the imported 2.6 litre V6 Capri in the 60s, now a four litre and in production for many years and fully debugged. A starter, an alternator.. maybe it was two alternators? Batteries, power steering pump, tires, brakes, and universals in the rear drive line. Of course this is my wife’s car, and If there was an egg taped to to the gas pedal, it wouldn’t have broken yet.. Cost of ownership is $80 per month less maintenance items and gasoline. Most will understand you can buy a LOT of gas with these kinds of savings… BUT there’s no bragging rigths, and perhaps the nut across the street from you calls you an SUV owner? The car still looks fabulous, and our near salt free area means there’s zero rust. The car looks better than many five year old rigs, and the emissions numbers are still same as new! but… we need not fool ourselves, this is no American effort, it’s made in 20 plus countries if I remember correctly.

      • George B. says:

        I need to add.. about 12 years ago.. I told my Wife we could afford to get her a new car IF she wanted one.. We went back to the same dealer here in Kent, they found all kinds of things wrong with the vehicle including the fact it didn’t have a VIN number in the door jam where it belonged… “musta been in one helleva accident and repaired?”. We politely told them the dealer had sold us the car with full assurance the car had been in a minor accident and repaired correctly with a full warranty from them, and further assurance that all new parts were used. Furthermore, it was >them< that had sold it to us.... They had offered $1500 trade in value on the new car... I'm not sure I have ever seen my wife so angry... well maybe when I caught her rose bush on fire, but that's another story.. Needless to say, the dealer soiled themselves... I've never given car salesmen much credit for thinking ahead as a collective, but we know better than to brand them all 🙂 G

        • Brian W. says:

          I’m glad you had such good fortune with that vehicle. But it’s too bad that some American cars and American car companies failed miserably on reliability. The worst vehicle I ever owned was an 87 Jeep wrangler. Unbelievable what I dealt with on that vehicle. Three vehicles after that were Toyotas, out of fear of getting another American lemon. Finally got enough courage to buy American again, but it took me 20 years to muster the courage.

          • George B. says:

            Brian, I’m sorry to say that you have a LOT of company. There are all too many major engineering disasters in American cars, but do keep in mind, the car story I share is about a car that carries the FORD badge only, there were indentical Mazdas built (as per the power train), so this really isn’t a story about an American success, it’s a car made in 20 countries or more. If you are inclined to note disasters, we’ll all note the TM200 tranny, the Vega block with only a thin coat of teflon keeping alum block and alum piston from destroying each other.. the many self destructign Chrysler trannys in small pickups, on and on.. As a nation, we might attempt to handicap the competition by gettiing the engineers who design such crap jobs in Europe, and Asia. Others might mention that we are insane enough to outsource our engineering, and perhaps the bad designs were done outside the country.. who knows.. All I offer is one example of a car done mostly right..but I didn’t mention the flaws… heavy braking might warp the rotors, the car is known to be a little top heavy, I think it’s a bad choice to tow with regardless of what ford says. We also keep in mind.. this is a wife’s car.. she drives like a little ole lady, but for goodness sake.. don’t say I said it… I hear the Boeing 787 engineering was outsourced… 🙂 Can’t be done inside any longer as boeign sold off it’s brain power. I’d imagine the engineering firm that came up with the design to attach the wings onto the tube said “oh well, we gave it our best shot” History now records that the 787 is 10 plus tons heavier than the first engineered design! That’s a lot of added material in critical areas to assure the wings don’t fall off 🙂

            The good news? the 787 will still save an Airlines a bundle on fuel over an Air Bus design,… The moral of the story? …perhaps it’s what I’ve said for years, hands on engineering is king… that means ‘your hands’ not someone elses! We learn it is our Ass when their hands fail..

  2. Michael L says:

    Kudos on the 2.6 liter engine. Very different then the 4.3 liter vortecs in the chevys. The joke, which holds somewhat true is, ” 4.3 = Gas mileage of a V8 and the power of a 4 cylinder”!!!!

    My repair data base on my truck is similar to yours. 140,000 miles. 2 sets of tires, 1 alternator, 1 water pump, 1 fuel pump, 1 battery. Standard brake repirs and fluid changes. Thats it in its 15 yr existance. Truck has paid for itself 2 fold. Sticker was 15,800. Today this truck will cost 28,000 to replace.. “ABSURD” in my opinion. I dont drive vehicles for status but for function.

    Another thing is when my fuel pump went I had a choice of dropping the tank or lifting the bed. Well it may seem hokey but I think of anyway to save me labor.

    What I did was stood in the bed of the truck with my diamond blade angle grinder. Lined up and measured where the top of the fuel pump is, and cut an access panel in the bed. Replaced pump and made a new plate to cover. Siliconed in place and secured with self tappers. Put the duraliner back in, DONE. Took less then one hour. My buddy did his on a blazer type and took him in access of 5 hours and a hurt back. I belive his filler neck is still leaking and or some vacuum vent issue.

    I cant afford to get hurt or waste time on something where I can reduce my labor by 2/3 rds.


    Like I said my way may seem hokey but really think about it for what it is.

    Here is something funny that may give some a chuckle.

    Anyway no swagger wagons for me yet. ( Sienna SE = swagger wagon)

    For those that dont know what a swagger wagon is sit through this kind of rap paraody. Its quite humorous if you have an open mind.

    I found it funny when I saw it.

    Mike NJ

  3. Tom V. says:

    I used to own a ’92 Exploder, and have seen a fair number of Fords with the Warner 1354 t-case came through with 4WD difficulties.
    A common thing I have found in these shifter motors, other than the contacts needing some dressing, is the selector shaft driven gear, located under that switch plate and the next “layer” further into the gear box. The selector motor drives a worm gear, in turn driving a 2″ diameter gear splined to the selector shaft. The driven gear has a little post which limits its travel, and this post is normally cushioned by a plastic bushing; this bushing dies and the pieces are often seen lying in the housing when you remove the gear. With the bushing gone, the motor can turn too far, causing unexpected inputs at the 4WD controller box, and resulting in erratic shifting or no shifting, often accompanied by a blinking 4WD indicator.
    Now for the good news: all you need is a short piece of vinyl tubing to replace the bushing, and you’re good to go. With your switch contacts dressed (don’t forget to lube them with vaseline or similar,) you’re off for another 100k miles of not worrying about your 4WD system.
    Hope this helps!
    Tom V.

    • George B. says:

      Thanks for you addition to this thread! Great info. That lube you mention, I wiped mine down good thinking the >lube< was the source of the no contact. Sounds like I may have done the wrong thing, but we use 4WD almost never, so maybe running dry won;t be that bad?

  4. Tom V. says:

    I use just a small amount of white lithium grease, just barely enough to give the contacts a protective coat. It’s going to be wiped anyway by the switch contacts. You don’t want it caking up on you, so a thin grease with a low drop point (stays thin and runny even at low temps) is the way to go.
    For those of us who do take our trucks through mud and muck, a little (very little!) silicone sealant on the rim of the cover and switch will serve to keep the nasties away from our hard work.

  5. Philip says:

    I have a 1991 Ford Explorer and just got back from a ski vacation where I used the 4WD a lot and really put my car under a lot of stress. Probably drove home too fast as well, a few times hitting 85 mph. What can I do to be sure my car is still in good shape and can survive another similar trip if I take one? You guys sound very knowledgable. Another odd thing: to completely disengage the 4WD, it’s not enough just to switch it off. You’re supposed to back up 40 feet or so (if memory serves) and then you will HEAR it fully disengage. But lately I never hear this disengage sound so I worry about that as well. Any advice?

    • George B. says:

      When you take a sharp corner on pavement and don’t feel your front tires fighting the turn, you are likely to be disengaged.
      When driving any 1991 Auto, you should always have cash enough for a tow truck. My wife refuses to buy a new car, her 1991 will need to die a screaming death in order for me to pry her hands from the steering wheel.
      But you need note, she has a bit of magic with her at all times, with her cell phone, she can call me or a tow truck IF anything were to go wrong.

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