Many posts about the power door locks used in the F150. After diving into the schematics and partially troubleshooting my own problem here's what this electrical engineer has learned:

(The following applies to a 2000 F150 XLT with remote keyless entry)

1. Door lock circuit consists of
a) door switches that are grounded when closed for either lock or unlock. (Different circuit in each case is grounded.)
b) three relays that send voltage & current to door actuators. One relay is dedicate to the driver door unlock function when RAP is included. The other relays control both doors. One for lock and another for unlock.
c) RAP module (optional equipment) that has two outputs that basically connect in parallel to the door switches. There is a third dedicated output and relay for opening just the driver side on a single key fob press. The RAP module also performs the auto door lock feature when you remove your foot from brake and tranny is in gear.

2. When pressing a door lock switch the relays under the dash are activated. You should hear a click near the top of dash under the access panel (panel that starts near top center of dash and goes off to the passenger side and has slots for the automatic headlight sensor). A door lock switch can be held closed and continuous voltage is applied to the actuators.

3. When using the key fob the RAP module will pull the same lock or unlock switch to ground. The biggest difference is that the RAP module will only pull the circuit to ground for about a half second then let go. On the first press a dedicated RAP output will just control the driver door through that dedicated relay. On the second press both doors are controlled (yes the driver's side get's two actuatons when you press the key fob twice.)

4. Please note that the RAP and switches control the same circuit prior to the relays. They are in parallel.

5. The actuators are really DC motors. They work in both directions. Voltage applied in one direction causes a "lock" and voltage applied in the other direction causes an "unlock". Only two wires are really needed at the actuator. But it seems there are more on mine. My schematics don't show more than two wires. Inside the actuators are thermal protection devices. Basically, these devices go high resistance when they heat up thus limiting the current through the motor and protecting the motor from burning up. You can cause these guys to heat up by holding the door lock/unlock switches down or repeated use of switches or key fob.

OK, my problem has been door locks that appear to be getting sluggish over time and eventually to the point that there just doesn't seem to be enough power in the actuators to move the mechanism. Both doors doing this at about the same frustration level.

One thought was dirty relay contacts since the problem was the same with switches or key fob. The relays were common to both sides and since both sides acted up at about the same time this made sense.

The relays are found under the top dash access panel. That piece of dash that looks like it can come off really does! No screws, just get the edge of your fingers under the end closest to the headlight sensor slots and pull up and work your way all the way around pulling up. With that removed there's a relay box right there. Sorry, but that's not it! You need to pop that one off the metal bracket and remove the bracket. It comes off easily. Under the metal bracket toward the engine is a relay box with a plastic cover. Once the cover is off I found the three door lock relays on the left and two others (auto headlight circuit?) on the right. All were the same part number so I simply did some swapping to see if symptoms changed. Nope! I even measured contact resistance and all were no more than 1.5 ohms. Very little compared to the rest of the circuit.

Since the relays checked out I could only think of two other possibilities:

1. High resistance in a ground circuit
2. The door acutators.

After reading many posts on door actuators I'm betting on that. To check for high resistance I could disconnect and fish the two-conductor actuator wire out of the door and connect a light bulb to it. I would then measure the voltage across the light bulb to see if the voltage was much less than about 11v. A light bulb is required to draw current and force a voltage drop across bad (high restance) connections.

Since the door actuators have a built-in thermal protector I am betting this device is going bad (high restance under normal temperature) and limiting the current to the motor resulting in weak action. It seems mine work better in cold temps. so this further supports the theory of bad thermal protectors.

I think I will order one or both actuators and intstall. I'll update after all the cuts and scratches heal



Roger

 

Great info but you stopped right where I need to begin. How do you actually install new actuators?

thanks

jc

 

there is a rivet in door that holds actuator need to drill out and remove then sometimes need to remove latch and window guide to get enough room to swing actuator off of latch. it has a hook bent into the end of the rod have to kind of swing it around and twist.

 

Yes, I did stop before the job was done! That's because after getting the latch loose and feeling my way around enough to remove the stinker I ran out of time and had to reverse my steps to put the truck back together so I could use it. I had spent considerable time tracing other possible causes before I got to the actuators. Could have saved a bunch of time & trouble had I come to this forum first

BTW, I did not have a rivet to drill out. I did have the latch and actuator loose from the door but I didn't see clearly how to get the linkages off. I counted three but I'm not sure if all need to come off to remove just the actuator part.

My dealer quoted about $236 including tax (6%), labor and parts to replace both sides. Actuators alone were about $56 each. I may spring for the extra $120+ to have them do it!

When I get the bad actuators out I plan to tear down and see what exactly is failing. That's just the engineer in me

Sorry I stopped short. Good luck!

Roger

 

thanks, I'll give it a shot.

jc

 

I'm having the same problem. Did you ever get them fixed?

 

I have the same problem. Waiting on your results before I dive in. By the way, my drivers side door was sluggish 1 - 2 months before my passenger door. Now both are totaly dead ! Took about 9 months to reach this point from first signs of weak performance.

 

My truck started the same exact thing, just in reverse order. My passenger side lock became weak about 3 months before my driver's side. Now neither automatic lock will work.

Just out of curiosity, are alot of people having trouble with this, and if so, what year model's are involved.

2000 F-150 Lariat 4x4 extended cab.

 

My passenger door has been dead for about a year now the drivers side is still fine.

 

OK, I finally got a chance to return to my door lock problem. Here's a detailed solution.

Summary: Door locks act weak and barely work if at all.

My findings: Carbon powder from the motor brushes accumulates inside motor providing an alternate path for current.

This, combined with warm days when the motor's thermistor is at a slightly higher resistance will cause weak or nonfunctioning door lock actuators.

Solution: The best solution is to replace the actuators. My dealer quoted $250 for both doors. Actuators can be found for about $30-$50 each on the web. For those on a budget and willing to do a little labor, an alternative is presented here. This involves removing the actuators, removing the motors inside the actuators and opening the motors to clean out the carbon dust.

Disclaimer: I did this repair to both doors on my F-150. The passenger side works great. The driver's side works most of the time but not like new. When it stops working I must wait about 10 seconds for the thermistor to cool down then try again and it usually works. I have not yet tested in hot weather.

I took many pictures throughout this process but I do not have a web site to post them. I can e-mail to somebody who does, however. (I will be gone for a couple of weeks so it will take a while to reply.)

Materials and tools needed:

1. #9 torx
2. long flat blade screwdriver
3. philips screwdriver
4. small short needle nose to open motor case
5. drill and a set of bits
6. 11mm socket and wrench
7. some #4 1/2" sheet metal screws to put actuator back together
8. Electrical cleaning spray (critical)
9. one or two bandages
10. a good facial grimace or two
11. about 2 hours of time

Instructions (2000 F-150 extended cab)

1. Make sure window is up then pop off vertical plastic trim above door panel
2. Pop off trim under inside door handle.
3. Remove two screws found under the trim pieces.
4. Pop up the panel with lock and window buttons. Lift the edge closest to door hinge first.
5. Disconnect connectors
6. Lift up on door panel to remove. Careful, lightbulb will still be attached!
7. Remove lightbulb. (Turn on interior lights and use this light as an aid later.)
8. Pull down the plastic stick-on barrier.
9. Remove 11mm bolt near door edge under latch to free up window guide.
10. Remove two more 11mm nuts to the horizontal metal bracket to make some elbow room.
11. Pop off the plastic lock button on top of rod.
12. Remove inside lock stem. There are two plastic holders. Reach behind the lower holder and squeeze to release. Pull rod down through upper holder. Leave hanging.
13. Use long flat blade screwdriver to snap open the holder for the outside door handle rod. This holder will be at the latch side -- not the door handle end. My snap holder was yellow. Once opened just pull the rod out.
14. The key lock rod is the hardest. Reach a couple of fingers behind the rod then use a flat screwdriver to pry open the plastic holder while pushing the rod out. This holder is hard to see and is hidden behind the window guide. Move the guide a bit to see the retainer.
15. Use a #9 torx to remove three latch screws
16. Now, holding your mouth just right, wiggle and turn the latch assembly to get it out. The rod that went to the door lock may fall off during this step. Remember that the small loop in the rod goes to the lock and the other end fits rather loose into a hole lined with plastic dip coating.
17. Disconnect wires to the actuator portion. Other wires can remain connected.
18. Remove the actuator. Use a flat screwdriver to pry up on a locking tab located between two metal guide rails. While prying up slide the actuator off the rails.
19. Drill out 6 plastic rivets. (Do not remove metal rivets at the end.) Use a drill bit slightly smaller than plastic head. Don't drill too deep. You will use a smaller bit to drill deeper to clear holes for the #4 screws used to reassemble the case.
20. Pry open the case and remove the motor.
21. Bend out metal tabs holding plastic motor back on.
22. You will likely find the inside cap and motor windings covered with a black dust. This comes from the wear of the brushes. This needs to be removed. I used an electrical cleaner called Electro-Clean. Spray your cleaner on and this powder should come off rather nicely.
23. I removed the small thermister element along one side and cleaned it off as well. Remove using a small needle nose. Do not loose this piece! Also, do not replace this piece with a short circuit or you will burn up your motor! The motor is not designed for a 12v stall current of about 4 amps!
24. Assemble motor and replace. Make sure two slots are up for the electrical connection. (Look inside housing and you should see two terminals sticking down that go into motor when the case is closed.)
25. Use 1/2" #4 sheet metal screws to close the case. It may be necessary to first use a small drill bit to clear a hole for the screws at each rivet location.
26. Slide the actuator back in place and connect the wiring.
27. For the fun of it, you can test at this point by reconnecting the door switch temporarily.
28. If the rod for the door lock came off earlier slip it on now.
29. Hold your mouth in whatever fashion worked for step 16 and wiggle the actuator back in place.
30. Before replacing the three torx screws, I reattached the rod for the door lock because it wants to float around a lot.
31. Now, replace three latch screws.
32. Pop the door latch rod into place and snap the keeper over it.
33. Slip the inside lock rod up through the upper holder and replace the lower holder. Put the plastic lock button on the rod now before you forget.
34. Replace 11mm bolt and two nuts.
35. Test again.
36. Replace plastic barrier, door panel and other trim.
37. It's possible that the plastic slot for the manual lock will cause additional friction during unlock. You might need to lubricate slightly or remove door panel and bend the rod a bit.

Hope this works for you! Again, I have not tested in hot weather yet.

Roger
n9sxz@arrl.net

 

First of all, thank you very much RogerD for the detailed instructions and the prompt reply to my email! My job would be much more difficult without this help.

I'm really on a budget, so replacing the actuators at $40+ a pop didn't seem like a good idea to me. I followed Roger's instructions and despite a good cleaning, they still didn't work.

I investigated the small rectangular thermistor found inside the tiny motor housing. Mine started off at 8 ohms when cold and went up to 20+ ohms when hot. When present in the curcuit along with the motor coils, the whole lot only has ~ 11 ohms of resistance cold. Thus, the motor has approximately 3 ohms of resistance. The 8 ohms the thermistor provides when cold is just too much. I think this has been speced incorrectly because the motor does not have the power to move the locks. I would suspect you can buy these items at an electronic store. If you are realy concerned about the termal protection they provide, that's probably the route you want to take. Just replace it with something with a smaller cold rating.

After thinking about Roger's warning about not bypassing the thermistor with a short, I decided to bypass the thermistor with a static resistor. Because the resistance is so low, I simply removed the thermistor and stuffed some solder in there. Solder really isn't a very good conductor, so it provides some natural resistance, so long as there is no copper core.

This makes the locks work exceptionally well. The motors do get hot, but they don't burn out. I would suspect that if you held the button down for a long period of time, bad things may happen, but the worst case is that you would have to replace the actuator which is what you were facing in the first place. Now, they work instantly and have lots of power.

G.

 

Seems that these actuators are a classic case of :

a) Simple design complicated by adding protection against idiots/children who would play with the locks until they burnt out

and

b) "value" engineering that replaced a proper thermal overload with a cheap thermistor

Thanks to all for the information

 

We have finally had some hot days here in Central Indiana. My locks are still working fine.

Greg, your warning is good and I'm glad to hear yours are now functional again. I was a bit concerned about removing the thermister altogether. Too bad the cleaning didn't work for you. I wonder if your linkage is tighter or has more mechanical resistance that calls for a stronger push/pull.

It's only the door switches that can be held on constantly -- not the remote key fob. So if you treat them normally like you said there should be no issue.

Roger

 

hmmm i was thinking they went from riveted on actuators to latch mounted in 2001. well i guess they change in 2000. the new ford ones do look different then the original 2001 model actuators. mount the same and have same connectors but a slightly different shape. i wonder if they redesigned them and they might work better then the older ones. i've seen lots of problems with 01 actuators but not too many on 02 or newer yet.

 

My passenger side became sluggish about 2 months ago and now the drivers side is doing the same thing. Both switches will NOT unlock the either thier own door OR the other.

200 F-150 Lariat 4x4 extended cab.

This forum is awesome