P0121
CIRCUIT DESCRIPTIONThe throttle position (TP) sensor is a potentiometer.
The powertrain control module (PCM) supplies the TP sensor:
1. a reference voltage
2. a signal
3. low reference 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 in order to determine the throttle blade angle, or opening.
This diagnostic trouble code (DTC) determines if the throttle position (TP) sensor signal input to the powertrain control module (PCM) does not closely match what the predicted value for the TP sensor should be. The PCM 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
^ DTCs P0112, P0113, P0122, P0506, or P0507 are not set.
^ The engine is running.
^ The barometric pressure (BARO) is not in default.
^ The throttle position is steady.
CONDITIONS FOR SETTING THE DTC
Stuck High Test
The TP is more than the calculated throttle position for more than 5 seconds.
Stuck Low Test
The TP 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) 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 (MIL) 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.
DIAGNOSTIC AIDS
The scan tool displays the TP in volts. The scan tool should display about 0.45-0.85 volts with the throttle closed and the 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 WOT.
Inspect 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, inspect the condition of the connector seal and repair or replace the seal as necessary. If DTC P0121 is intermittent, refer to Intermittent Conditions. Intermittent Conditions
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 inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagnostic Aids.
TEST
