DTC P0123: Throttle Position Sensor Circuit, High Input: Condition

WARNING: This page is about a different car, the 2002 Mazda Protege5 and 2002 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when input voltage from Throttle Position (TP) sensor is more than 4.90 volts after engine starts. This is a continuous monitor. MIL is illuminated when PCM detects malfunction during first drive cycle. Possible causes are:

Open or short circuit between PCM and TP sensor.
PCM malfunction.
TP sensor malfunction.