Powertrain Management (CNG)

DTC P0123

Circuit Description

The throttle position (TP) sensor is a potentiometer. The powertrain control module (PCM) supplies about 5 volts on the TP sensor reference voltage circuit. The PCM also supplies a ground circuit to the TP sensor. When the throttle is pressed, the TP signal voltage rises to near the supplied 5 volts. As the throttle is released, the TP signal voltage drops to around 0.6 volts. The PCM and the Alternative Fuels ECM monitor the TP signal circuit voltage and determine the angle of the throttle blade.


This DTC sets when the TP sensor signal voltage is above the normal operating range of the sensor.


Conditions for Running the DTC

The engine is operating on alternative fuel.


Conditions for Setting the DTC

The Alternative Fuels ECM monitors a TP sensor signal voltage of greater than 4.9 volts for at least 1 second continuously.


Action Taken When the DTC Sets




* A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History.
* The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails.
* The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.



Conditions for Clearing the MIL/DTC




* The Last Test Failed status will clear when the DTC runs and passes.
* The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.
* The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.
* All DTC Information can be cleared with a scan tool.



Test Description

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the condition is present.
3. This step determines if the TP signal is going high only when the throttle is opened.
4. This step determines if the condition affects the PCM.
5. This step determines if the TP signal circuit is the shorted condition.
6. This step determines if an open sensor ground circuit is the cause of the condition.
7. This step determines if the 5-volt reference circuit is shorted to a voltage. 5.2 volts is the maximum voltage that the PCM should supply on the 5-volt reference circuit.