P0121
Diagnostic Chart:
Wiring Diagram:
Circuit Description
The Throttle Position (TP) sensor contains a potentiometer whose resistance value changes along with the throttle valve position. The Powertrain Control Module (PCM) provides a 5 volt reference voltage to the TP sensor. The PCM reads the voltage across the TP sensor and converts it into the throttle position. The TP sensor resistance decreases as the throttle valve opening increases. When the TP sensor resistance decreases the voltage being monitored at the PCM will increase. And when the TP sensor resistance increases, because the throttle valve opening is decreasing, the voltage being monitored at the PCM will decrease.
Conditions for Running the DTC
^ Engine speed is between 1500 and 3000 RPM.
^ Engine coolant temperature is greater than 70°C (158°F).
^ Intake air temperature is between -10°C (14°F) and 50°C (122°F).
^ Fuel level greater than 25%.
^ Barometric pressure greater than 75 kPa.
^ Manifold Absolute Pressure (MAP) change is less than 13 kPa/16 firing events.
Conditions for setting the DTC
^ Difference between expected TP sensor and actual input is greater than 11°.
^ The above condition is met for at least 3 seconds.
Action Taken When the DTC Sets
^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.
Conditions for Clearing the MIL/DTC
^ The MIL will turn OFF after three consecutively passing cycles without a fault present.
^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.
^ DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.
Diagnostic Aids
Check for any of the following conditions:
^ A poor connection at the PCM. Inspect the harness connectors for backed out terminal, improper mating, broken locks, improperly formed or damaged terminals, and a poor terminal to wire connection.
^ A damaged wiring harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the TP display on the scan tool while moving connectors and wiring harnesses related to the TP sensor. A change in the TP display will indicate the location of the fault.
^ A misadjusted TP sensor or a binding or stuck throttle plate could cause the malfunction to set. Refer to Throttle Position Sensor / Adjustments for TP sensor adjustment procedures.
^ Before replacement of the TP sensor check the resistance of the TP sensor, between terminals 1 and 4 - 2.87 to 5.33k ohms, and terminals 1 and 3 - 100 to 20k ohms. Replace the TP sensor if not within these values.
If a DTC P0121 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
If any wiring repairs need to be made, Refer to Repair Procedures in Electrical Diagrams.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. Vehicle must be at operating temperature and a feeler gauge of the specified size must be used. If a TP sensor voltage parameter is available use the parameter instead of a Digital Multimeter as a method of diagnosis.
5. Checks the TP sensor signal circuit for a short or a open. also check the TP sensor ground circuit for a open.
7. The TP sensor adjustment must be checked and set to specifications. Replace the TP sensor if proper adjustment cannot be made. Refer to Throttle Position Sensor for TP sensor adjustment and replacement procedures.