Circuit Description
The DTC P0121 Throttle Position (TP) Sensor 1 Performance diagnostic detects an out of range sensor signal. The TP sensor 1 output provides the powertrain control module (PCM) with a signal voltage that is proportional to the throttle plate movement. The TP sensor used with the throttle actuator control (TAC) system is actually a Hall Effect switch. The Hall Effect switch is surrounded by a magnetic yoke that induces a flux in the magnetic field when the throttle shaft is rotated. The PCM provides a 5-volt reference voltage to the sensor circuits in the TAC module. An integrated circuit (IC) receives and converts the magnetic pulses into two separate TP signal, each with their own characteristics. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens. TP sensor 1 determines the actual throttle valve position. TP sensor 2 has a voltage that is more than twice that of TP sensor 1 at idle. TP sensor 2 provides a backup value for TP sensor 1.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0121 Throttle Position (TP) Sensor 1 Performance
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | DTC P0121 runs continuously once the above condition has been met. |
Conditions for Setting the DTC
The difference between the TP sensor 1 signal and the TP sensor 2 signal is less than 0.8 volt for at least 2 seconds.
OR
The difference between the TP sensor 1 signal and the TP sensor 2 signal is more than 1.6 volts for at least 2 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM stores the conditions that were present when the DTC set as Freeze Frame data. |
| • | The engine will operate in the reduced power mode and the TP sensor angle will default to 19 percent. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip in which the diagnostic runs without a fault. |
| • | The PCM clears a History DTC after 40 consecutive warm-up cycles without a fault. |
| • | You use the scan tool Clear DTC Information function. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check - Vehicle 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.
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This step determines if DTC P0121 is the result of a hard failure or an intermittent condition.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | |||
Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | ||
2 | Are there any other throttle position (TP) sensor DTCs set? | Go to Step 3 | |
Does DTC P0121 set? | Go to Step 4 | Go to Intermittent Conditions | |
4 | The TP sensor in the throttle actuator control (TAC) module is faulty. Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Did you complete the replacement? | Go to Step 5 | -- |
5 |
Are any DTCs displayed on the scan tool? | Go to Step 6 | Go to Step 2 |
6 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
