I Picked up this 1998 Dakota 3.9, it has been sitting since 2009, did a tune up changed fluids repaired brakes. Now I have Got this code PO0123, verified TPS was working properly. Unplugged connector found that Ground was good, 5volt supply was good, but I had 5 volts on the signal wire. Checked wires back to PCM all appear good, continuity and no resistance
Reconnected connector started truck OBD showed 86% at idle and decreased upon acceleration(just the opposite of what it should be)
Ideas on where to start.
I reset the PCM
I am thinking that something is back feeding but what
Moparite,
I got the reading by unplugging the TPS connector and with the key on I had 5volts on the supply and on the signal wire from the PCM. My understanding is that there should not be any voltage in the signal wire until its connected to the TPS and it should increase as the throttle opens. I have checked all the grounds In the engine compartment cleaned and reconnected them. I did reset the PCM by disconnecting the ground for 30 seconds with the key held in the start position shut key off and then reconnected the negative and held key for at least 5 at the on position
I am looking for advice on where to start looking for the short.
I don't know if this is related but the right rear tail light does not work, brake and turn signal work fine, and I did change the bulb.
You need to check the voltage with the connector hooked up not disconnected. The voltage you are reading is from the electronics inside the pcm. Turning the key on with the tps disconnected will throw a code because the pcm isn't reading anything from it. I don't recall what the exact voltage sweep you should be reading but i think it's about one volt at idle and up to the 4.8 at wot. Just replace it, It's an easy and cheap part. You dont have a short you have a over voltage reading!
Common Problems That Trigger the P0302
Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable)
Incorrect ignition timing
Vacuum leak(s)
Low or weak fuel pressure
Improperly functioning EGR system
Defective Mass Air Flow Sensor
Defective Crankshaft and/or Camshaft Sensor
Defective Throttle Position Sensor
Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems
I would look at these for your misfire Po302 Number 2 cylinder, you can also try and swap plugs with another cylinder to see if the code follows that cylinder and better you can do a power check to see if the injector is bad, while running at idle disconnect the injector plug on #2 cylinder and you should notice the power drop by rpm, if not the injector is then faulty
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