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DTC P0123: Throttle Position Sensor #1 High: Testing

NOTE: Ensure throttle is fully closed and free from binding or carbon build-up.
  1. Start the engine. With the DRBIII®, read the TP Sensor voltage. Is the voltage above 4.5 volts? If yes, go to next step. If no, turn the ignition off and go to step  8.
  2. Turn ignition off. Disconnect TP Sensor harness connector. Disconnect the PCM harness connectors. Measure the resistance between the TP Sensor Signal circuit and the 5-Volt Supply circuit at the TP Sensor harness connector. Is the resistance below 100 ohms? If yes, repair the short between the 5-Volt Supply circuit and the Throttle Position Sensor Signal circuit. If no, go to next step.
  3. Ensure the ignition is off. Reconnect the PCM harness connectors. Turn ignition on, engine not running. Measure the voltage on the TP Sensor Signal circuit at the TP Sensor harness connector. Is the voltage above 5.2 volts. If yes, repair the short to battery voltage in the TP Sensor Signal circuit. If no, go to next step.
  4. Turn the ignition off. Connect a jumper wire between the TP Sensor Signal circuit and the Sensor Ground circuit at the TP Sensor harness connector. Turn ignition on, engine not running. With the DRBIII®, monitor the TP Sensor voltage. Is the voltage below 0.5 volt? If yes, replace the TP Sensor. If no, go to next step.
    5. CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal-to-pin connection. Use Miller Special Tool (8815) when performing diagnosis at PCM harness connectors.
  5. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance of the Sensor Ground circuit from the TP Sensor harness connector to the appropriate terminal of the Miller Special Tool. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the Sensor Ground circuit.
  6. Measure the resistance of the TP Sensor Signal circuit from the TP Sensor harness connector to the appropriate terminal of the Miller Special Tool. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the TP Sensor Signal circuit.
    7. NOTE: Before continuing, check the PCM harness connectors for corrosion, damage or terminal push out. Repair as necessary.
  7. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
    8. NOTE: Throttle linkage must be moved very slowly while looking for a smooth change in voltage in this step.
  8. Turn ignition on, engine not running. Using scan tool, monitor TP sensor voltage. Slowly open and close throttle plate while monitoring TP sensor voltage. Does the voltage start at approximately 0.8 volt and go above 3.5 volts with a smooth transition? If yes, go to next step. If no, replace the TP sensor.
    9. WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
  9. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Look for parameter values to change and/or a DTC to set. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
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