P0121

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor is a potentiometer. The TP sensor is mounted to the left side of the throttle body. The TP sensor provides a voltage signal that changes relative to throttle blade angle. This signal voltage is one of the most important inputs used by the PCM. The TP sensor has a 5.0 volt reference, a ground and a signal circuit. TP sensor Signal voltage should be about 0.6 volt at idle. The TP sensor voltage should increase to above 4.0 volts at wide open throttle (WOT). This diagnostic compares actual throttle position from the TP sensor to a predicted throttle position value. The predicted throttle position is calculated from engine speed and other inputs. If the PCM detects the predicted throttle position is below the actual TP sensor value, this DTC will set.

CONDITIONS FOR RUNNING THE DTC
- No MAP sensor or TP sensor DTCs set.
- The engine run time is greater than 10 seconds.
- The engine coolant temperature is greater than 0°C (32°F).
- The IAC is between 0 and 255 counts.
- The MAP is less than 55 kPa.
OR
- The MAP is greater than 65 kPa.
- MAP steady.

CONDITIONS FOR SETTING THE DTC
- The predicted throttle angle does not match the actual throttle angle.
- All conditions present for 20 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the Malfunction Indicator Lamp on the second consecutive drive trip that the diagnostic runs and fails.
- The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The PCM turns the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
- A last test failed (current DTC) clears when the diagnostic runs and does not fail.
- A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
- The PCM battery voltage is interrupted.
- Use a scan tool in order to clear the MIL/DTC.

DIAGNOSTIC AIDS
- The following may cause an intermittent:
- Mis-routed harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation.
- The PCM 5.0 volt reference circuits are internally connected within the PCM. If all the TP sensor circuits are OK, inspect the Fuel Tank Pressure Sensor for malfunctions.
- If it is determined that the DTC occurs intermittently, performing the DTC P1121 diagnostic table may isolate the cause of the fault.
- For an intermittent, refer to Symptoms. Testing and Inspection

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. If DTC P1639 sets at the same time, this indicates that the 5.0 volt reference circuit is either shorted to a ground or shorted to a voltage. The 5.0 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 checks 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.
9. Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicated the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For an intermittent condition, refer to Symptoms. Testing and Inspection

11. This checks the 5.0 volt reference circuit, signal circuit, and the PCM. If the scan tool displayed 5.0 volts, the TP sensor circuits are OK.