P0121

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle opening. The TP sensor signal voltage varies from about 0.6 volts at idle to about 4.8 volts at Wide Open Throttle (WOT).

The TP sensor signal is one of the most important inputs used by the VCM for fuel control and for most of the VCM control inputs.

CONDITIONS FOR SETTING THE DTC

The following conditions will set the DTC:

^ No TP sensor short DTCs

^ No IAC DTCs

^ No MAP DTCs

^ Engine running

^ BARO not defaulted

^ Change in TP is less than 1.9%

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

ACTION TAKEN WHEN THE DTC SETS

The VCM turns ON the MIL after 2 consecutive driving cycles with the fault active. The TP sensor reads 0% if the vehicle speed is less than 2 mph. The TP sensor reads 10% if the vehicle speed is greater than 2 mp/h. The scan tool will show a defaulted value.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.

^ 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 exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery teed for 30 seconds.

DIAGNOSTIC AIDS

The scan tool displays the throttle position in volts. It should display 0.20 volts to 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. Testing and Inspection

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 to 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 or a damaged linkage. If the throttle and the linkage are okay, continue with the diagnosis.

4. With the TP sensor disconnected, the TP sensor voltage should go low if the VCM and the wiring are okay.