P0121

CIRCUIT DESCRIPTION

Schematic:

The Throttle Position (TP) sensor is potentiometer used to indicate the amount of throttle opening. The PCM supplies the TP sensor with a voltage reference and a ground. The TP sensor provides a signal voltage to the PCM relative to throttle blade angle. With the throttle closed, the PCM should detect a low signal voltage. At wide open throttle, the PCM should detect a high signal voltage. The PCM checks the TP sensor to ensure that the sensor is functioning properly. The PCM predicts a TP sensor value based on MAP, and engine speed. The PCM compares the predicted value to the actual TP sensor input. DTC P0121 will set if the actual TP sensor input does not closely match the predicted value.

CONDITIONS FOR RUNNING THE DTC
^ No MAP, IAC or TP sensor DTCs tailing.
^ The engine is running.
^ ECT is more than 0°C (32°F).
^ AC valve position is between 10 and 160 counts.
^ MAP is less than 55 kPa to check for a stuck high TP signal.
^ MAP is more than 63 kPa to check for a stuck low TP signal.
^ Traction control inactive
^ Engine over-temp inactive

CONDITIONS FOR SETTING THE DTC
The actual TP sensor input does not match the predicted value.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) the first time the malfunction is detected.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL OFF after the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool Clear DTC Information function.

DIAGNOSTIC AIDS

NOTE: Refer to Connector Test Adapter Kit J 35616-A Notice in Service Precautions.

If the conditions is intermittent, refer to Intermittent Conditions in Symptoms. Intermittent Conditions

TEST DESCRIPTION

Steps 1 - 9:

Steps 10 - 19:

The numbers below refer to the step numbers on the diagnostic table.
2. If DTC P1635 sets at the same time, this indicates that the 5 volt reference circuit is either shorted to a ground or shorted to a voltage. The 5 volt reference circuit is internally connected within the PCM.
3. The MAP value should change with the engine speed. If a MAP sensor voltage changes, there is no malfunction with the MAP sensor.
4. This step tests for an intermittent connection at the sensor.
8. If the TP sensor voltage changes, there is no malfunction with the TP sensor wiring or the PCM.
11. This tests the 5 volt reference circuit, signal circuit, and the PCM. If the scan tool displayed 5 volts, the TP sensor circuits are OK.