P0121
Stpes 1 - 7:
Steps 8 - 12:
DTC P0121 TP Sensor Circuit Range/Performance Problem
Circuit Description
The throttle position (Throttle Position) sensor circuit provides a voltage signal that changes relative to throttle blade angle. The signal voltage will vary from about 0.25 volts at closed throttle to about 4.75 volts at wide open throttle (WOT).
The Throttle Position (TP) signal is used by the powertrain control module (PCM) for fuel control and most of the PCM-controlled outputs. The PCM monitors throttle position and compares actual throttle positions from the TP sensor to a predicted TP value calculated from engine speed. If the PCM detects an out-of-range condition, then a DTC code P0121 will set. DTC P0121 is type A code.
Conditions for Setting the DTC
- The Engine is running.
- No MAP, ECT, TP, CKP, EGR, EVAP or DTC's are set.
- IAC is between 10 and 160 counts.
- ECT is above -10 °C (14 °F).
- The MAP value changes by less than 2 kPa.
All the above mentioned conditions are met, and one of the following conditions occurs for a total of 12.5 seconds over a 25-second period of time.
Stuck High-
- MAP value is below 55 kPa.
- Actual TP value is greater than the PCM's estimated TP value (Estimated TP value is based on MAP and RPM).
Stuck Low-
- MAP value is below 50 kPa.
- Actual TP value is less than the PCM's estimated TP value (Estimated TP value is based on MAP and RPM).
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 Diagnostic Trouble Code was set as Freeze Frame and in the Failure Records data.
- The PCM will use a default throttle position based on MAP 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 Diagnostic Trouble Code P0121 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P0121 can be cleared by using the Scan Tool's "Clear Info" function.
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.
- 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; an open circuit, a short to ground, or a short to voltage. If the harness appears to be OK, observe the MAP 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 or P1121 Diagnostic Chart may isolate the cause of the fault.