P0121

DTC P0121 Throttle Position (TP) Sensor Circuit Range/Performance Problem:

Throttle Position (TP) Sensor Circuit:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle opening. Signal voltage will vary from about 0.6 volt 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 Vehicle Control Module-A (VCM-A) for fuel control and for most of the VCM-A control inputs. P0121 is a type "B" DTC.

DTC PO121 WILL SET WHEN
^ No TP sensor DTC's set or failures flagged.
^ No Manifold Absolute Pressure (MAP) sensor DTC's set.
^ Engine running.
^ MAP sensor is less than 60 kPa (18 Hg).
^ Throttle Position changes less than 1%.
^ The last throttle position value is greater than calculated throttle position based on engine speed.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
The VCM-A will turn on the Malfunction Indicator Lamp (MIL) after two consecutive driving cycles with the fault active. TP sensor will read 0% if vehicle speed is less than 2 mph and 10% if vehicle speed is greater than 2 mph (scan tool will show defaulted value).

DTC P0121 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. 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-A will use that value as closed throttle. If the reading is out of the auto zero range at closed throttle, check for a binding throttle or damaged linkage, if OK, continue with diagnosis.
2. With the TP sensor disconnected, the TP sensor voltage should go low if the VCM-A and wiring are OK.

DIAGNOSTIC AIDS
A Tech 1 scan tool displays throttle position in volts. It should display 0.20 volt to 0.90 volt with the throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Also, a Tech 1 scan tool will display throttle angle %, 0%=closed throttle. l00%=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. A DTC P0121 may result from a restricted air intake system such as an air filter or a collapsing air intake duct.

If DTC P0121 is intermittent, refer to Diagnosis By Symptom. Testing and Inspection