P0121

Circuit Description
The Throttle Position (TP) sensor is a potentiometer. The Control Module (PCM/VCM) supplies the TP sensor a reference voltage, signal, and ground circuits. When the throttle is depressed, the TP sensor signal rises to near the reference voltage. When the throttle is released, the TP sensor signal decreases from the reference voltage. The Control Module monitors the TP sensor signal circuit voltage to determine the throttle blade's angle (or opening).

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

Conditions for Setting the DTC

Stuck High Test
The throttle position is more than the calculated throttle position for more than 5 seconds

Stuck Low Test
The throttle position is less than the calculated throttle position for more than 5 seconds

Action Taken When the DTC Sets
^ The Control Module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
^ The Control Module will set the DTC and records the operating conditions at the time the diagnostic fails. The Control Module stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC
^ The Control Module 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 start-up 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 about 0.45 volts to 0.85 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). The scan tool will read the throttle angle percentage. 0 percent equals closed throttle. 100 percent equals Wide Open Throttle (WOT).

Check the condition of the connector and the sensor terminals for moisture or corrosion, and clean or replace the terminals as necessary. If corrosion is found, check the condition of the connector seal and repair or replace the seal as necessary. If DTC P0121 is intermittent, refer to Symptoms. Symptom Related Diagnostic Procedures

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.

Test Description
The numbers below refer to the step 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 volt, the VCM uses that value as a closed throttle. If the reading is out of the auto zero range at the closed throttle, check for a binding throttle shaft or a 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 and a DTC P0122 may set.
16. Reference voltage less than 4.5 volts could cause a poor TP performance condition. Be sure to check both 5 volt 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.