P0121
DTC P0121 TP System Performance
Circuit Description
The Throttle Position (TP) sensor is a three wire potentiometer using a 5 volt reference, a ground and a signal circuit. The TP sensor signal circuit detects voltage changes on the potentiometer (variable resistor) as the throttle angle changes. The TP sensor signal voltage varies from 0.6 volts at idle to approximately 4.6 volts at wide open throttle. The TP sensor is one of the primary inputs to the VCM. Its input is important to most engine and transmission functions.
This DTC determines if the TP sensor signal input to the VCM does not closely match what the predicted value for the TP sensor should be. The VCM calculates what the TP signal voltage should be based on engine RPM. If the TP sensor voltage and the predicted TP sensor values do not closely match, this DTC will be set.
Conditions for Running the DTC
- DTC P0122 not active
- No active IAC DTCs
- No active MAP sensor DTCs
- The engine is running
- BARO not in default
- The throttle position is steady
Stuck High Test
MAP is less than 50 kPa
Stuck Low Test
- Stuck high test has passed
- MAP is greater than 65 kPa
- The IAC is between 10 - 340 counts
Conditions for Setting the DTC
The calculated throttle position is less than the actual throttle position for more than 5 seconds.
Action Taken When the DTC Sets
- The VCM illuminates the MIL (Malfunction Indicator Lamp) if a failure is detected during 2 consecutive key cycles.
- The VCM will set the DTC and records the operating conditions at the time the diagnostic fails. The VCM stores the failure information in the scan tools Freeze Frame and/or the Failure Records.
Conditions for Clearing the MIL/DTC
- The VCM turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
- A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22 °C (40 °F) from the startup coolant temperature and the engine coolant temperature is more than 70 °C (158 °F) during the same ignition cycle).
- Use the scan tool Clear Information function.
Diagnostic Aids
The scan tool displays the throttle position in volts. It should display 0.20 - 0.90 volts with the throttle closed and ignition ON or at idle. The voltage should increase at a steady rate as the throttle is moved toward Wide Open Throttle (WOT). Also, the scan tool displays the throttle angle %. 0% = closed throttle. 100% = WOT.
Check the condition of the connector and sensor terminals for moisture or corrosion, and clean or replace as necessary. If corrosion is found, check the condition of the connector seal and repair or replace as necessary. If DTC P0121 is intermittent, refer to Symptoms.
An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs.
Steps 1 - 4:
Steps 5 - 11:
Steps 12 - 18:
Steps 19 - 23:
Steps 24 - 25:
Test Description
The numbers below refer to the numbers on the diagnostic table.
2. The TP sensor has an auto zeroing feature. If the voltage reading is within the range of about 0.2 - 0.9 volts, the VCM uses that value as a closed throttle. If the reading is out of the auto zero range at the closed throttle position, check for a binding throttle shaft or damaged Linkage. If the throttle shaft and the Linkage are okay, continue with the diagnosis.
3. The TP sensor throttle angle should range smoothly from 0 - 100 percent when the throttle is slowly depressed to the wide open throttle (WOT) position. If not, a skewed out of range TP sensor, low reference voltage or a poor connection could be possible causes.
6. With the TP sensor disconnected, the TP sensor signal voltage should go low if the VCM and the wiring are okay.
16. Reference voltage less than the 4.5 volts could cause a poor TP performance condition. Be sure to check both 5 volts reference circuits for conditions that could cause low voltage on the TP sensor circuit.
19. The throttle shaft, throttle Linkage or accelerator cable not closing due to sticking or binding could cause a TP sensor poor performance condition.