I know this has been talked about before, but searching has not found the answer I am looking for. I recently purchased a 2004 F150 SCSB, 5.4, auto. It has the dial switch on the dash for the 4x4. I can get the truck to go into 4lo (light on the dash comes on, tested truck, 4x4 is locked in), when the truck is shifted into neutral, but will not shift into 4hi (no light, tested truck, no 4x4). I can hear the motor working on the transfer case. I have pulled the connector off of the IWE solenoid with the switch in the 2wd mode, and have 14+v, when I turn the switch, it does not change. I pulled the vacuum lines off, I have vacuum on the lower line, nothing on the top, I hooked up the lower line only with the switch on and off and I get no change from the top port of the switch. What should I be looking for here? What worries me the most is that from other posts I have read, it could be the PCM, which is big money. Any help or advice will be greatly appreciated. In the meantime I will keep searching through past posts to try and find a solution. I'm used to the old get of the truck and rotate the lockouts and then put the transfer case shifter in 4x4 to engage, not caring for this electronic crap.

 

Have you tested the switch on the dash itself?

 

Are you taking the lines off the solenoid mounted beside the PCM? If so you are only going to have vacuum on one of the 2 lines. One line comes from the engine providing vacuum to the solenoid and one line goes to the IWE's. This system works differently than the previous generation fords. The IWE's at the wheel have vacuum applied to them to keep the truck out of 4x4 when when vacuum is removed the 4x4 engages. So if the motor is in fact shifting the transfer case remove the lines from the solenoid beside the PCM and plug the line with vacuum then shift it into 4hi and test. Otherwise you could have an issue with the transfer case motor. I have replaced many transfer case motors at work. Another thing you can do is find someone that has a scantool like a snap-on solus or access to a Ford IDS and scan the 4x4 module for codes. Hope this helps you a little.
Andy

 

Andy, I understand how the vacuum system works now, my issue I have is why am I not see a change in voltage going to the IWE solenoid when I switch into 4wd. What bothers me the most is that it will go into 4wd lo, just not high. I guess my next step is take the switch out the dash and check to see if it working correctly like Jon mentions.