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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 48368
Experience:  16 years experience
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Need help to fix 4x4 problems in my 2004 Ford F150

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I have an issue with my 2004 F150 4WD system. I checked the voltage at the vacuum solenoid with the 4WD switch in 2WD, 4WD high and 4WD low. I always have 14V there. Any ideas? I can hear the 4WD high engage as well as the 4WD low, but the indicator for the 4WD high just lights briefly (sometimes) and then goes out. 4WD low seems to always work if I'm in neutral when I switch it.

Hello and thank you for choosing Just Answer.

There have been many issues with the 4x4 solenoid on the firewall causing many different 4x4 issues. One of them being the 4x4 light may not come on. To properly diagnose, the vehicle should be scanned for trouble codes in the Generic Electronics Module or GEM. C1979 and C1980 are the codes that would be in the module.

Customer: replied 5 years ago.

I don't have a scanner for this particular vehicle. Just point me to a schematic and I'll be happy. I can sort it out from there.

The problem lies with water that runs off the cowl panel and gets ingested into the solenoid which causes the problems.

Customer: replied 5 years ago.

Well then, why do I always have 14V at the solenoid no matter what position I put the switch in?

The pink/light blue wire at the solenoid is hot at all times which means it always has battery + voltage. The PCM controls the red wire circuit. The switch does not directly tie into the solenoid.

Customer: replied 5 years ago.

Well, I measured the open circuit differential voltage across the terminals (with the solenoid disconnected). As you have described it, the PCM pulls the voltage on the red wire low when it wants to energize the circuit. I always have voltage across the terminals which indicates the the PCM is not being told to 'release' (that is, the red wire is always pulled low). I suppose this could be due to some leakage current somewhere, but the volt meter that I'm using has a 10Mohm input impedance. I could place a load across the terminals and confirm this.
I just need a schematic. I have the Haynes manual which is useless in this case.
Beyond all of this, I have snow in the drive way and when I'm in 2WD I spin, 4WD high and low seem to be working. I'm just concerned that possibly only one hub is engaging.


When in 4 high does the dash light show its engaged? When in 4 low do you get a reduced gear ratio as well as a 4 low light?

You asked about the wire diagram is that all you want here?

Customer: replied 5 years ago.

When I switch from 2WH to 4WH I occasionally get a 'blink' out of the light, but it does not stay on. If I place the truck in neutral and then switch to 4WL the light comes on after a second or so. It definitely feels like I have both 4WH and 4WL functionality, but I'm not 100% sure that both hubs are locking in.
A schematic would be great.

Ok, without doing any diag so far it looks like multiple issues. Even if the front hubs are not locking in, the light on the dash will still work. The front hub lock in components have nothing to do with the light on the dash. The encoder plate inside the shift motor on the transfer case turns on the lights. So its looking like a faulty shift motor. Now if you also think its locking in but its not locking in the front axle, then odds are you have a faulty integrated wheel end IWE solenoid mounted on firewall next to the battery. However you need to check the IWE hubs and the hoses as well for restrictions. On this model, vacuum is applied to the hubs to keep them unlocked. Below is some Ford information that can help out.

Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 48368
Experience: 16 years experience
Chris (aka- Moose) and 2 other Ford Specialists are ready to help you
Customer: replied 5 years ago.

I now have the truck sitting up on jack stands (all four wheels off the ground). When I start it and place it in drive while in 2WD only the rear wheels turn. This is good. When I switch to 4WDH, the front wheels spin (recall that the 4WDH light blinks occasionally when I do this) so I know that the HUBs are engaging and the shift motor is working (I can hear the shift motor move). When I switch to 4WDL while in neutral I can hear the motor again and the front wheels still spin. So, the mechanical system is working and the feedback from the encoder seems to be flaky. There are 5 wires to the encoder. I assume power, ground, 2WH, 4WH and 4WL?? Should I be looking for 'active high' signals or 'active low' signals? Or is this one of those quadrature encoders with a direction signal?

Here below is how to diagnose the light issue.

Below is the wire diagram associated with the tests.


Customer: replied 5 years ago.

Ok, I'm at step R7 and have a 'no'. "Goto pin point test L". I'm thinking maybe I should spend the $100 at Napa and just buy the aftermarket transfer case motor. Is there any way to separate the case on the encoder without destroying it?

Pinpoint L is for a truck not even shifting into 4wd, which is not your case. Yes you can open a shift motor to check for pin arcing or water intrusion. So far the signs are pointing to the shift motor encoder portion causing this.

Customer: replied 5 years ago.

I had the encoder off earlier today, but it didn't look like I could get inside it to clean any contacts that are inside. I agree with you, the encoder seems to be giving the wrong information to the instrument cluster. I have not been able to find a place where I could just buy the encoder. Everyone sells the entire motor assembly.
I assume that 'contact plate position' means POS1 thru POS4 resistance to SIG RTN right? Leave it to Ford to take a simple three position sensor and use 5 wires:)

I don't have a shift motor to check. I thought there were screws holding the casing together. I assume you would have noticed them. If there are none then they are glued together. Why they made it confusing I do not know. I rarely ever even do the diagnostics anymore. I let the Ford scan tool tell me what is wrong and then try one of our known good test parts. Many repairs are done this way.

Customer: replied 5 years ago.

Yeah, I have a PC based scanner for my other cars, but not for the Ford. There are three screws holding the encoder to the case, but once the encoder is off it seemed to be moulded together. Maybe I'll pull it back off tomorrow and have another look.

Keep me up to date if you do not get it resolved tomorrow
Customer: replied 5 years ago.

Ok, so I thought I had identified the problem at the encoder, but I was wrong. I put a new motor/encoder combo on and I have the same problem. 4WH light blinks occasionally but won't stay on.
Any suggestions?

Are you sure you went through the test correct?

When the light is blinking is it actually kicking out of 4wd high and not working or it is just the bulb blinking from a possible bad connection in the cluster?

Customer: replied 5 years ago.

The light flicks on for ~0.25 to 0.5seconds when I switch from 2WH to 4WH. This happens about 50% of the time. In either case it always seems to engage the 4WD system.

So it only flickers the first time you go into 4wd high then it just stays off, but you do have 4wd and drive to the front wheels?

Customer: replied 5 years ago.

Correct, I get a quick flick from the light and then it goes out. This only happens occasionally but in all cases the 4WD engages.

You are going to need a scan tool to monitor the 4x4 module and instrument cluster to see if the module is not commanding the light on and to see if the cluster is even being signalled to have the light on then command the light on manually with the scan tool and see if the light fails to light like it should.

Customer: replied 5 years ago.

I was afraid of that. One thing I do know for sure is that the light works and the instrument cluster can turn it on. It comes on when I turn the key to on prior to starting the car.
Do you know of any decent scanners that I can buy at an auto store?

No auto parts scan tool is going to have this ability. The IDS we use at the dealer is about 3300$

Customer: replied 5 years ago.

That sucks. The PC based tool that I have for my Audi allows me to access anything I want.

You could buy the program and connection tool from ebay but its not cheap.

Customer: replied 5 years ago.

Where is the PCM and is there a wiring diagram for it? I should be able to locate the problem that way given that I know that the system can turn the 4WD light on.

Customer: replied 5 years ago.

Scratch that... know what pin numbers I'm looking for at the PCM, but don't know where the PCM is. The pin numbers are shown on one of the wiring diagrams that you sent to me.

The PCM is between the battery and the #4 cylinder on the firewall.

Customer: replied 5 years ago.
OK, thanks. I'll take a look tomorrow.

You are welcome.

Customer: replied 5 years ago.

Ok, now I have the problem 'surrounded'. If I disconnect the vacuum lines from the IWE solenoid I can engage and dis-engage the hubs using a short piece of vacuum line to complete the vacuum circuit. I confirmed that functionality by engaging the hubs and spinning the wheels which in-turn spins that half shafts. When I dis-engage the hubs, the half shafts don't spin with the wheels.
Next, I put a 1Kohm resistor across the electrical terminals of the connector that attaches to the solenoid. This fools the computer into thinking there is a solenoid attached. With the resistor in place the 4WH light works.
End result: My solenoid failed open. In this case, the hubs remain engaged and the transfer case decides whether or not the front wheels spin. The computer must look at the current to the solenoid to determine if 4WH is engaged.
Thanks for your kind assistance. I have a new solenoid on order.

Thanks for the update. You taught me something as well, I never knew the IWE solenoid had any effect on the light. I have seen way too many solenoids bad and the lights still worked. The only thing I can assume was a internal issue and it was throwing back feedback messing up the module. Any how great job and I am glad you figured it out.

Customer: replied 5 years ago.

I believe that if the solenoid failed short then the light would still come on. Mine failed to open so the light didn't work. From what I've read, the solenoid typically fails short.

Thanks again for the update.