P0121

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor is used by the PCM to determine the throttle plate angle for various engine management systems. The TP sensor is potentiometer sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit. The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to more than 4 volts through the TP sensor signal circuit. When the conditions for running this DTC are met, the PCM will use the MAP sensor in order to determine if the predicted operating range of the TP sensor is correct. When the TP sensor voltage is out of this predicted range, DTC P0121 sets.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0122, P0123, P0107, P0108, P1123, and P1122 are not set.
^ The engine run time is more than 2 minutes.
^ The engine coolant temperature is more than 70°C (158°F).
^ The MAP is less than 40 kPa.

OR

^ The MAP is more than 67 kPa.
^ The MAP is steady.

CONDITIONS FOR SETTING THE DTC
^ The predicted throttle angle does not match the actual throttle angle.
^ All conditions are present for 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC "Last Test Failed" clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
A skewed MAP sensor may cause this DTC to set. If the TP sensor is operating properly, and if this DTC continues to set, test the MAP sensor for proper operation.

The PCM 5-volt reference circuits are internally connected within the PCM. If all the TP sensor circuits are OK, inspect the MAP sensor for malfunctions.

If it is determined that the DTC occurs intermittently, performing the DTC P1121 diagnostic test may isolate the cause of the fault. Refer to DTC P1121. P1121

TEST DESCRIPTION

Steps 1-8:

Steps 9-14:

Steps 15-19:

The numbers below refer to the step numbers on the diagnostic table.
2. If DTC P1635 sets at the same time, the 5-volt reference circuit is either shorted to a ground, or is 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 does not change, this test indicates a map sensor fault.
4. This step tests for an intermittent connection at the sensor.
9. Using Freeze Frame/Failure Records data may help to locate an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can help to determine how many miles have occurred since the DTC set. The Fail Counter and the Pass Counter can also help to determine how many ignition cycles have occurred since the diagnostic reported a pass and/or a fail. In order to isolate when the DTC failed, operate the vehicle within the same Freeze Frame conditions that you observed. These conditions include the RPM, the vehicle load, the vehicle speed, and the temperature.
11. This tests the 5-volt reference circuit, the signal circuit, and the PCM. If the scan tool displayed 5 volts, the TP sensor circuits are OK.