P0121

Steps 1 - 7:

Steps 8 - 12:

DTC P0121 Throttle Position (TP) Sensor Circuit System Performance




Circuit Description
The throttle position (TP) sensor circuit provides a voltage signal that changes relative to throttle blade angle. The signal voltage will vary from about 0.6 volts at closed throttle to about 4.5 volts at wide open throttle (WOT).

The TP signal is one of the most important inputs used by the powertrain control module (PCM) for fuel control many of the PCM-controlled outputs. The PCM monitors throttle position and compares actual throttle position from the TP sensor to a predicted TP value calculated from engine speed. If the PCM detects an out-of-range condition, DTC P0121 will set.

Conditions for Setting the DTC
- The engine is running.
- No MAP DTCs, or P0121, P0122, P1122, P0123 DTCs are set.
- MAP reading is below 55 kPa.
- Throttle is steady, throttle angle is changing less than 1%.
- Predicted throttle angle is not close to actual throttle angle.
- Above conditions are present for a total of 12.5 seconds over a 25-second period of time.

Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) after the second consecutive trip in which the fault is detected.
- The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.
- The PCM will use a default throttle position based on mass air flow and RPM.

Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A history DTC P0121 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P0121 can be cleared by using the scan tool Clear info function or by disconnecting the PCM battery feed.

Diagnostic Aids
Check for the following conditions:
- Skewed MAP signal or faulty MAP sensor - An incorrect MAP signal may cause the PCM to incorrectly calculate the predicted TP sensor value during high engine load situations. Check for an unusually low MAP reading. This condition can cause DTC P0121 to be set.
- The TP Sensor shares a 5 Volt reference with the EGR valve. If these codes are also set, it could indicate a problem with the 5 Volt reference circuit or components itself.
- The TP Sensor shares a ground with the EGR Valve and the IAT Sensor
- Poor connection at PCM - Inspect harness connectors for backed-out terminals, improper mating, broken locks improperly formed or damaged terminals, and poor terminal-to-wire connection.
- Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

If DTC P0121 cannot be duplicated, the information included in the Failure Records data can be useful in determining vehicle mileage since the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1122 and DTC P1121 Diagnostic Charts may isolate the cause of the fault.