W. Ball

Hi all. I am new here and have a question. My 98 F-150 4.6Ls 4x4 will not engage. I did some searching first but couldn't see any posts regarding my issue.

Heres the low down. I just recently got it back from the garage for an A/C repair today. Now I live in a climate in northern Canada that the temperatures are extremely cold -20C to -40C in the daytime. I got in the truck and I had it in 2WD when I picked it up from the shop (Temp outside is -22C) I selected the 4x4 switch to place it in 4x4 and could not here the solenoid click at all and it would not engage. It seems theres no power gettin to the switch. But it could be cold related too. Is there any suggestions on to what the issue could be if its not cold related? This has never happened before and I checked with the garage to see if anyone was around any components of the 4x4 system and they said no. I exercised the switch a few times and even placed the truck in "N" and reversed about 20ft to see if anything would work but nothing. Any suggestions will be greatly appreciated?

kirklandkie

I too have had some issues with my 4x4 system in my 97 f150. In all my reading it seems the number one point of failure was the vacuum system. Check all of your hoses under the hood and look for abrasions or cracks. The other point of failure is the solenoid valves (top left of engine bay). Water gets up in them and they freeze and crack. If all of the electric parts of the system are working then you should be able to put a finger on the top of them and feel them engage when someone flips the 4x4 switch.
good luck

-Kirk

W. Ball

Thanks Kirk. But I done some troubleshooting last night. There is no power going to the vacuum soleniods behind the battery, my friend was switching the 4x4 selector back and forth and there is no clicking on the solenoids. First I checked the fuse, Its oK. Then I went to the vacuum lines and didn't see any issues with those. Then I decided to check the plugs on the soleniods, theres 12V going to them, there OK. So I jumped each solenoid to ground to test to see if they worked, bypassing the Generic Electronic Module (GEM). As we turned the selector they both did click so it seems theres an issue with a relay somewhere or even the relays within the GEM. Do you know of any relays anywhere in the system that controls the selector?

It seems to me when you select the switch, power is sent through a relay to activate the vacuum solenoids to either engage or disengage the transaxle. I'm leaning towards an electrical issue somewhere but finding the relays is my next question. Any thoughts?

86 aero

Check the 30A fuse under the hood. I think it's number 104. Oops you already did that.

kirklandkie

If your solenoids are working when jumped then it is certainly electrical. Not sure where the 4x4 relays are off hand, i think they are listed in the owners manual. If they prove to be good and the 4x4 switch also bench tests as good i'd suspect a bad GEM. The windshields in our model year are notoreous for leaking water (down onto the GEM). Remove the GEM and inspect for water damage, if there is water damage replace the GEM and get your windshield resealed. Having never replaced a GEM i did mine in about 2 hours and paid about 60 bucks for a salvage yard GEM. Good luck

-kirk

kirklandkie

Oh also my understanding is that when you switch into 4x4 the GEM applies ground to the solenoid valves which completes the circuit turning them on