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.
I took off the IVS, sprayed contact cleaner into it, and ohmed it out, works great, on and off. Placed it back on the pedal, opens and closes, clicks...so I know that there is an on/off state being generated.
Also ohmed out the old and new TPS. Resistance was higher in the old TPS versus the new one. 3.6 ohm between the outside pins and 167 ohms from the end to center pin. The old TPS had a reading of 600+ ohms from the end pin to center. Thought that may be a problem.
With key in on position and TPS plugged it.
Put the hot lead in the middle wire
Ground to battery
Slowly push down in go pedal watching the volts
At idle you should have 0.7v
Wide open throttle should be 4.5v
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Whatever you're using to get the codes, it reads live data, right? Have you tried just watching the TPS value as a %age with the key on, and slowly pushing the pedal? You should also be able to get the 1/0 status of the IVS, and determine when it switches on relative to the pedal position.
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