[CREWZIN]

I did some checking on PT Do-It-Yourself.net and this is what it said:

I have a 2001 TE PT with 98k miles. The engine light came on and self tests reveal a P0123 fault code. I have tried to find pictures, diagrams, and easy to understand info on how to correct this code. The probable causes stated on the info from Auto Zone say the sensor open or shorted internally-replace component. Thanks. – Kathy, from Texas.

The P0123 fault code indicates: Throttle Position Sensor Voltage High - Throttle position sensor input above the maximum acceptable voltage.

The P0123 fault code is for the circuit, not the sensor. You can check the connector, however other causes include:

Throttle Position Sensor Sweep
Intermittent Condition
TP Signal Circuit Shorted To 5 Volt Supply Circuit
TP Signal Circuit Shorted To Battery Voltage
TP Sensor Internal Failure
TP Signal Circuit Open
Sensor Ground Circuit Open
PCM

Voltage and continuity measurements need to be performed. The power and ground circuits need to be verified. I admire your willingness to jump in with both feet, but unless you have experience with a voltmeter, DRB scan tool, diagnostic/service manuals, and familiarity with the electronic systems within the PT, you would be better served by seeing your local dealer for diagnostic help.


Now, personally, you had to take off the (UM) upper manifold to get to the thermostat. The UM is attached to the (TB) Throttle Body, So is the TPS (Throttle Position Sensor). It's located in back of the TB next to the IAC (Idle Air Controller) (See Haynes Manual you used for the thermostat). I suggest you take a good look at the TPS and IAC and see that you haven't dislodged any connections and make sure everything is tight. Check the clips to the wiring and all screws and bolts. I don't think the TPS would go bad just after the thermostat so check everything you touched, then, take off the negative battery terminal for 5 minutes (wiping out old codes) and see if the P0123 comes back. I don't think it will. Please let us know what you find.

P.S. The Multi-function switch should have nothing to do with your TPS problem.