OK, I'll try to make a long story as short as I can. I had the code P0303 appear on my pocket scanner a few days ago, looked it up and discovered it indicates a misfire on #3. I've had to have 2 or 3 COP coils replaced on my 2002 EB 5.4L Expedition over the 13+ years that I've owned it, and replaced the coil to fix a #1 misfire myself a couple of years ago, as that is the only one that I have the tools, patience and level of expertise to tackle on the Expy. All the rest of them (with the possible exception of #2) I'll gladly leave for the pros. Anyway, I wanted to remove the #1 spark plug to verify which plugs the motor has in it, so yesterday afternoon I removed the #1 coil and put my spark plug socket w/attached extension on it into the spark plug well and onto the plug so I could remove it. Unfortunately, the plug had seized in the aluminum head and I was unable to remove it. The socket had latched onto the plug, so the extension pulled out of the socket when I attempted to pull it off the spark plug. I tried to remove the socked with the only needle-nose pliers I could find in my garage, to no avail. I resigned myself to taking the Expy to my trusted mechanic to work on this morning, but because I was concerned that driving it without the #1 COP plugged into the spark plug might toast the coil, I removed it and tossed it into the cabin to take with me. I also left the #1 fuel injector electrical lead unplugged as an extra measure to be sure gas wouldn't get injected into a 'dead' cylinder. I stopped in a parking lot on the way to the shop to connect my pocket scanner again out of curiosity, and it indicated diagnostic code P0351 in addition to code P0303. Looked it up and learned that code means "Ignition Coil A Primary/Secondary Circuit Malfunction". Would I be correct in assuming that Ignition Coil A is for cylinder #1 and that the code was set as a result of the fact that the coil was not connected? If that's the case, if the DTC P0351 is erased when the spark plug is replaced and the coil is reinstalled, is it not likely to reappear? By the way, I did not see a code P0301 appear after driving with the coil removed.

 

That is correct and the code will clear when you fix the connection issue.