P0121

DTC P0121

CIRCUIT DESCRIPTION
The throttle position (TP) sensor is a potentiometer type sensor that varies resistance according to changes in the throttle plate position. The TP sensor wiring includes three circuits. The powertrain control module (PCM) supplies a regulated 5 volts to the sensor on a 5-volt reference circuit. The PCM supplies a ground on a low reference circuit. The TP sensor provides a signal voltage to the PCM, relative to the throttle plate opening, on the TP sensor signal circuit. With the throttle closed, the TP sensor voltage is low, near 0.5 volt with the throttle wide open, the TP sensor voltage is high, near 4.5 volts.

Within the PCM, the intake flow rationality diagnostic has the ability to determine an inaccurate input from the three systems that it monitors. Calibrated within the diagnostic are estimates for the manifold absolute pressure (MAP), the mass air flow (MAF), and the TP for all engine operating conditions. The diagnostic compares the estimated values to the actual sensor inputs. It the PCM detects that the TP sensor input is not within a calibrated limit of the estimated value, DTC P0121 sets.

CONDITIONS FOR RUNNING THE DTC
- DTCsPO1O2, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0335, P0336, P0401, P0403, P0404, P0405 are not set.
- The engine coolant temperature (ECT) is between 70-121°C (158-250°F).
- The intake air temperature (IAT) is between -7 and +60°C (19-140°F).

CONDITIONS FOR SETTING THE DTC
The PCM detects that the TP sensor voltage is not within the calibrated limit of the estimated value for more than 1 second.

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 (MI L) 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.

TEST DESCRIPTION

Steps 1-2:

Steps 3-7:

Steps 8-15:

The numbers below refer to the step numbers on the diagnostic table.
7. This step calculates the resistance in the 5-volt reference circuit.
8. This step calculates the resistance in the low reference circuit.