Tim, good thinking, I will try to jump those posts and see what I get. Based on the wiring diagram above (post #2) I want to try to jump between post 86 and post 30 on the relay, with the other relay in, correct?

Thanks,

Baatzy

 

Hold on. Let me look.

No! Stay away from 86 and 85! Those are the low voltage coil terminals which go to and from the PCM. If you touch them with the 12v hot coming off of terminal 30 you will fry your PCM! So right now I am going to suggest that you disconnect your PCM to take it completely out of the circuit.

Now this is my understanding (but you should look at your relay it should have a diagram on it and in a book) that terminal 30 in a relay is 12v hot always on. And that terminal 87 in a relay is always the terminal which leads to the electric motor in question.

Warning: I don't know what I am doing. I just did this yesterday and I posted it so others could help me learn what I am doing. Don't do what I did below without independently confirming it is the right thing to do in your situation (or even in my situation because I don't know what I am doing).

Let's say you have an Electric Motor of some sort (e.g., a fuel pump or an electric auxilary radiator fan, etc.) and you know it isn't working (e.g., your engine won't start and you can't hear the fuel pump hum when you turn the key to "on" or you can't see the elec. aux. radiator fan turn when you know it should be turning).

Is it the Electric Motor, or the Wiring, or the Fuse, or the Relay, or the PCM that's broken?

First we need to understand what these components do and what order they are placed in to complete a circuit and send electrical power to energize the Elec. Motor in question. Let's take the elect. aux. radiator fan which I diagnosed in my wife's Dodge Dakota yesterday.

I was getting a P1491 trouble code and a check engine light on her Dakota. From the internet I learned that P1491 was an "open aux. radiator fan circuit." Which could mean that anywhere in the "circuit" there was something broken. The engine was also overheating and I could see that the electric auxilary radiator fan was not turning to provide additional cooling when needed.

Reading the forums for my wife's Dakota I found that the electric auxilary radiator fan is turned on by the PCM (the vehicle's "computer") when either: 1. the engine coolent temperature exceeds 195F or 2. the airconditioning is on. The vehicle's PCM contains a software program which monitors various sensors to know what's happening in the physical world (engine rpm, ABS, engine coolant temperature, vehicle speed, etc.). For example, when the coolant temperature sensor tells the PCM that the engine is getting too hot or that the airconditioning is on which will definitely make the engine too hot, the PCM somehow turns on the elec. aux. radiator fan to provide additional engine cooling (not all vehicles have an elec. aux radiator fan, my van does not). But the PCM's low voltage/low amp electrical current is way too weak to power the elec. aux radiator fan which requires a full 12 volts and at least 10 amps to spin those big fan blades fast enough to pull cool air through the radiator to cool the water in the radiator which circulates to the engine to prevent it from overheating. Although the PCM doesn't have enough voltage or amperage to power up the aux. elec. radiator fan motor, it is strong enough to flip a switch (like the light switches in our homes).

A relay is just an electromagnetic switch. I.e., the relay contains a coil of wire inside. So, when the PCM sends its low voltage/low amperage electrical current through the coil inside the relay, that coil becomes magnetic, which attracts a metal swing which pivots on a post which is hooked to a wire which goes to the electric motor (in our case the elec. aux. radiator fan) to touch another post which is hooked to a wire which comes from the Fuse which comes from the vehicle's 12v Battery.

The PCM's low voltage/low amp electrical current goes through the coil of wire causing it to magnetize which attracts the metal swing on post #87 to touch post #30 which sends the big 12volt 10 amp current through post #87 to the elec. aux. radiator fan which turns the fan a spinning. When the PCM stops sending the low voltage/low amp current to the relay, the coil loses its magnetism and the metal swing swings back "open" and breaks the circuit and the 12v 10 amp current from post #30 can no longer cross to post #87 and the fan loses electricity and stops.

The completed "circuit" goes like this:

12v car Battery -> Wiring -> Fuse -> Wiring -> Relay -> Wiring -> Elec. Motor (e.g., fan, fuel pump, etc.) -> Ground (either on 12v Battery or to vehicle chassis)

Any interruption in that circuit and your Elec. Motor won't run.

Here's the troubleshooting approach that I took yesterday to find out whether it was the elec. aux. radiator fan, or the Wiring, or the Fuse, or the Relay, or the PCM that was broken in my wife's Dakota. Look in your manual (I own the complete shop manual set purchased on ebay for each of the vehicles we own)* or the internet and:

1. Locate the Fuse which protects the Elect. Motor you are diagnosing and make sure that the Fuse is not blown. I just looked at the Fuse but it is better to test it with a battery powered test light probe or a multimeter. If the Fuse is ok, go on.

2. Locate the Relay which switches the Elec. Motor you are diagnosing. The Dakota's looks like this:

Note: I am having trouble uploading this other image. So look at the one below. See the diagram to the left of the Terminal Legend? That funny looking thing between terminals 85 and 86 is a coil (i.e., a magnet) when magnetized by the PCM's low voltage current flowing from 85 to 86 that coil magnetizes and physically pulls that little metal hinge/swing thing over to make the contact between the 12v hot at terminal 30 to connect it with terminal 87 which runs to the motor to energize the motor with the full 12v current that the motor needs to run.

Take a 16 gauge wire, put one end in the relay terminal receptical for post #30 (or whatever receptical in the terminal which is coming from the Fuse from the 12v Battery) and the other end in the terminal for post #87 (or whatever receptical in the terminal which goes to the Elec. Motor you are diagnosing). If your Elect. Motor runs (e.g., your fans spins or your fuel pump pumps) then you know that the Wiring from the 12v Battery to the Fuse to the Relay Terminal post #30 and the Wiring from the Relay Terminal post #87 to the Elect. Motor and the Elect. Motor itself are not broken. When I jumped Relay Terminal post #30 to Relay Terminal post #87 the elec. aux. radiator fan started spinning. (So, apparently, if the engine was overheating out in the boonies, we could just jump the relay terminals to power the fan and drive home.)

Comment from Dakota-Durango.com: The receptacle corresponding to Pin 30 on the relay is always hot and connects the relay to the fuse & battery. The receptacle corresponding to pin 87 on the relay goes to the electrical motor. While jumping pin 30 & pin 87 is a valid test, I wouldn’t recommend doing this unless you are absolutely sure that you know which receptacles correspond to which pins in the relay. If you get it wrong you could potentially send a ton of current down to the PCM and blow a fuse if you’re lucky or fry the PCM if you’re unlucky. Or you could send full current to ground and produce a nice big spark/shock. So be careful.

3. Buy a new Relay (they are under $20) and/or take a known good relay from somewhere else in the power distribution block and stick it into the Relay Terminal which you are diagnosing and see if your Elec. Motor works when it should (e.g., the elec. aux. radiator fan motor spins when the engine coolant exceeds 195F or the airconditioning is on, or the fuel pumps hums when you've turned the key to "on"). If the Elec. Motor now works, it was your Relay which was bad. If the Elec. Motor doesn't work, it is your low voltage/low amp Wiring from the Relay Terminal to the PCM or the PCM itself which is bad. Then I stupidly wrote: "Wiring doesn't often fail." WRONG!

Comment from Dakota-Durango.com: " That is incorrect. Wiring actually fails more often then the components they attach to in my experience. Think about it. Wires are fairly thin and it doesn’t take much to break or damage them. As the old saying goes, mechanics go to the part while electricians go to the wires. A lot of times the wires fail by inadvertently rubbing against something due to the normal vibrations a car produces. Simply puncturing the plastic coating around a wire creates a vector for moisture to get in and corrode the wire from the inside out. Corrosion on a wire causes excessive resistance which will cause all sorts of problems. Not to mention bad grounds

You hadn’t ruled out the wiring between the coil side of the relay and PCM or ground. A series of voltage drop tests would answer that question fairly quickly."

And as stated above and in my Contact Enhancer vs Dielectric Grease vs Micro Files thread here, it was not the PCM it was the 32-pin connection to the PCM which had corrosion in the bullet connector.


Note: The picture of the cut open relay as well as other good pictures of cut open relays is from:

Black Fuel Pump Relay - Dead One Cut Open - Pics - evolutionm.net


Baatzy: Hopefully others more knowledgeable than me can pipe in.


If there is any interest, I may clean this up and post it as a separate thread over here on the 7..3 forum for trouble shooting electrical motors, since the principles are the same across vehicles and engine types.

 

Yep, I was just reading your post in the other forum, looks like I want 87 and 30. Good thing you're quick, I didn't even have time to finish dinner.

Edit: I like the idea of disconnecting the PCM, I will do that, as I am currently pleased with the fact that my truck runs....

Thanks,

Baatzy

 

Yup, first "Do no harm."

Hope it helps and Good luck!

 

Double post.

 

Well I just got done digging in it again. On the shift relays it is actually pin 30 that goes to the load (motor) and pin 87 which is constant power, the same as the wiring diagram (post #2). I jumped one of the relay positions from pin 87 to pin 30. On the other relay position i grounded pin 30 to the negative terminal on the battery. With this setup I crawled underneath and measured across the connector that attaches to the shift motor and i got somewhere in the neighborhood of 12.5 volts (battery voltage). So from the relay box to the shift motor is good.

I also pulled out the PCM to make sure I didn't fry it. When I had it out I looked at both the male and female sides of the connector, looked flawless to me. I also pulled the PCM apart to get a look at the board, it looked just fine as well. I pulled apart all the connectors going through the firewall and the connector on the inner fender well, they all look clean as well. I can't find a trace of corrosion anywhere. It seems to me that my last option is to pull the wiring harness out and cut it open and inspect all the wires.

Edit: I fully reassembled everything and tried it out again, still no joy.

Baatzy

 

So does jumping 30 to 87 (with PCM disconnected) energize the shift motor?

 

I didn't try it with the shift motor because I didn't want to screw up the alignment with the "shifting shaft" on the transfer case. It did read 12.5 or so volts across the connector though so I don't see why it wouldn't work. I can go hook up the motor though and try again.

Baatzy

 

Hmmm, can't comment on alignment on the shifter shaft in the transfer case, but I can say that when I jumped 30 to 87 the aux radiator fan motor engaged in the Dakota and when I jumped 30 to 87 on the Bronco I could (barely) hear the (bad) fuel pump energize in the tank.

If jumping makes the motor works, then the coil in your relay is not getting energized. Which IMHO means either:

The relay itself is bad.
So put a known good same relay in its place (from another location). Or buy a new relay (what I did).

Or the wiring from and to the PCM from that relay terminal is bad. Continuity test time (I like a simple test light).

Or the plug to and from the PCM for that terminal is bad. Continuity test time (I like a simple test light).

Or the part of the PCM circuit board for that terminal is bad. Hmmm. Take it apart and look at it if it is not "potted."

Or there is a sensor whose job it is to tell the PCM that "Hey PCM, it is ok (or it is not ok) to engage the transfer case" (i.e., we are driving slow enough, etc.) which is another totally different circuit (but I don't think sensors have relays in the circuit but maybe they have fuses or even inline fuese to protect the PCM if the sensor shorts out? I don't know.) which may be open (i.e., "broken") such that your PCM wiring relay etc are all good on the transfer case motor side, but the safety sensor circuit is not functioning so the PCM won't activate the coil in the relay for the transfer case. Time to look at your wiring diagram (the oem Ford book for the make and model of your rig is on ebay and they are great books) and then its: "Continuity test time."

 

Yes, the PCM - or in this case thru the GEM - says when it is ok to engage 4lo. Otherwise, you should be able to go from 2wd to 4hi any time the key is on.

You can put 12v to the motor and spin it if you need to fix alignment. It will rotate either way by switching polarity. Just don't let it keep turning when it stops - it will break something. The compound planetary gearset produces lots of torque!

There is a switch on the motor assembly that reports (to GEM) what position the motor/shifter is in. The GEM then decides where it should be based on dash switch position and moves accordingly.

 

Well, I've got a known good shift motor, stole it from my dad's truck. I've also got known good relays, tested them on dad's truck as well. Best I can tell all the connections look good, both the PCM and GEM circuit boards look good. I may have to find and buy the oem manual now.

Or find and drive over a cliff.......


Thanks for all the help so far,

Baatzy

 

Just the 2001 Wiring Diagrams:


http://www.ebay.com/itm/2001-FORD-F-250-F-350-F-450-F-550-EXCURSION-WIRING-DIAGRAMS-MANUAL-/221699114399?pt=LH_DefaultDomain_0&hash=item339e4c059f

I have the one for my 2002 E-Series, but I couldn't find the wiring diagram for the transfer case in it.


Wait just one minute! That's why I had to pay $15K to have it converted to 4wd...

 

Thanks for the link.

Hahaha, I sure hope for that 15k you got a nice never fails manual transfer case.

Baatzy

 

That wiring diagram that whitetmw posted for you is probably all you need. I do most of my best problem solving while I am asleep. So, based on my experience, stare at the diagram now that you know the terminal legend likely applies to the various relays on there, and think about all the connections that flow from the **** that you touch with your fingers trying to figure out what combination of relays and that solenoid have to do to energize that "M" on your transfer case assembly.

My guess is that S250 is the PCM's low voltage input to the K378 and KJ39 relays.

If you disconnect the PCM and jumped those two relays would the motor energize? I don't know, I have other things I have to stare at tonight.
But you will figure it out if you stare at it long enough and others step up to help.*

The Wiring Diagram book will likely not only have the diagram but will also have a troubleshooting procedure.

But stare at the diagram until it starts to make sense to you. You have been under there enough times disconnecting and reconnecting things to have it make sense or to start to make sense to you now that you know the relay terminal legend and function. They are just friggin' switches.



* There are no doubt some really brainy FTE brothers out there who if they weren't laughing at how ineffective I have been at helping you, could step up and suggest a better way to trouble shoot your problem!

 

Tim, you've been great, so far all your ideas I have followed have led me to proving parts good, so that's definite progress. I am just getting worn out by this thing fighting me, especially because it seemed to just randomly take a dump on me. It never really gave me a good suspect area when it failed.

I think we have it narrowed down to the couple feet of wiring on the inner driver side fender well, and possibly the GEM. The GEM looks pristine, and I have absolutely no other issues, but the system doesn't even respond to my switch,like its just a toy on the dash, POS!

The others who have contributed have pointed out good things as well. This issue seems to be far outside the normal realm of 4x4 issues though, so its got us all stumped for now.

I just need to get my motivation up to tackle this again.






6.0s are at decent prices on CL.....

Baatzy