P0121

DTC P0121

Circuit Description

The throttle position (TP) sensor is used by the powertrain control module (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 manifold absolute pressure (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, this DTC sets.


DTC Descriptors

This diagnostic procedure supports the following DTC. DTC P0121 Throttle Position (TP) Sensor Performance


Conditions for Running the DTC

- DTCs P0106, P0107, P0108, P0122, P0123, P1122, and P1123 are not set.

- The engine is operating for more than 10 seconds.

- The engine coolant temperature is more than 0°C (32cF).

- The idle air control (IAC) valve is between 0-255 counts.

- The MAP is less than 55 kPa.

OR

- The MAP is more than 65 kPa.

- The MAP is steady.


Conditions for Setting the DTC

- The predicted throttle angle does not match the actual throttle angle.

- The condition exists for 20 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.

- Clear the MIL and the DTC with a scan tool.


Diagnostic Aids

DTC P0121 Steps 1-7:

DTC P0121 Steps 8-16:

- 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 DTC occurs intermittently, performing the DTC P1121 diagnostic test may isolate the cause of the fault. Refer to DTC P1121.P1121