I hope you have found it by now. It has been a while since I did this job, but I remember having to cope with a heat shield that curved back and down. My guess is that it is on the back side of the heat shield, meaning you would need to go under the truck and feel on the backside of the shield, if your arms are thin enough. A flexible rod of some sort might help if your arm cannot get up there to find it. If I am remembering correctly, you will be searching between the heat shield and the firewall.
Most of the entries on this item are older, but I thought I'd add to it since a recent p2285 code showed up. I am an older guy, very used to wrenching albeit not a professional mechanic. Obviously that code requires that the icp be changed. Since it is winter, and I have had a couple of health issues, I thought that I would have my local dealer make the change, although I thought long and hard about that because I don't like going to the dealer for a variety of reasons. I researched this swap and while not trying to offend the dealer told him what I knew about it (lots of research on the net reading the forums and searching for parts). I asked him if he had a good diesel mechanic (yes) and if he was built like an Olympic weightlifter or an agile amazon monkey because long, thin arms were required. Somewhat scared of the outcome, I left my truck. The next morning the service manager called me and said the transmission had to come out; that there was no way they could change the sensor without the removal. Putting on my best behavior not wanting to appear a total ass, I asked him what I owed him, the transmission wasn't coming out because it was not necessary and I would come and rescue my truck and do the job myself. I asked him if they had the sensor which they did and agreed to buy it (already opened and if opened could not be returned - $190.00 Ford p/n 3C3Z-9F838-EA for my '03 6.0 lit diesel). They did not have the pigtail or the p/n which tells me they are not familiar with changing these sensors. Not only that but they could not even get 5C3Z-12224-A.
I bought my '03 F350 new Feb of '04 and except for a warranty item and one recall, it has been maintained by me. Only other problem other than the FI stickion problem that plagues the 6.0, this is the only problem in 81k miles. Based on what I've learned on the net and thanks to you guys on the Diesel Stop, I am looking forward to changing this sensor and will when the weather breaks after the holidays. I believe it can best be removed from underneath, but that the connector replacement will have to be done topside. I will post when the job is completed. The one thing I wanted to pass on is that it is my understanding that regarding this particular part it is not if it will fail, but when it fails. When yours goes on the fritz, assuming you have a Navistar power plant, buy and use the International sensor p/n 1845274C92. This is an International engine, no doubt an International part will work as will many others, thus avoiding expensive Ford pricing. I found one on a diesel parts site on the net displaying the correct International part number for $22.99. I did not pursue the connector pigtail since I bought one from Amazon displaying the correct Ford p/n for $11 and change. Thanks again for your discussion and guidance.