I have an 04 with the 4.6 and had the low coolant temp or insufficient coolant temp code and it was the thermostat had locked open...replaced it in under 20 minutes and back on the road no problems. Hope this helps!
2004 F150 Supercrew XLT 4x4 4.6L | 83K Mi.
Edge Evo, K&N, SS Nerf Bars, Tool Box, 5100s
Ranch Hand Grill Guard w/IPF Hybrid Assist Lights
2.5 Ft/2.0 Rr, 285/75/17 Toyo MT, Magnaflow 2.5