This one really has me baffled! I read the codes for my 1996 F250 7,3L Diesel and it showed that the TPS is bad. Installed a new one still the same condition and malfunction. I took off the pedal, cleaned it as well as the small micro switch, ohmed it out that works and installed it. Cleared out the trouble code started it up and the same P0221 came back. Also had P0476 (back pressure) P0123.

I then took off the TPS, manually depressed the pedal so the relay would engage and turned the TPS with a screwdriver. No change All of the fuses are good under the hood and in the interior fuse panel.

Is there a relay under the hood (if so where) that does not come up in the malfunction codes? Anything else I am overlooking? All other tests I have performed on it do not show any other malfunctions.