Circuit Description
The throttle position (TP) sensor is a potentiometer. The TP sensor is mounted on the side of the throttle body. The TP sensor provides a voltage signal that changes relative to throttle blade angle. This signal voltage is one of the most important inputs used by the powertrain control module (PCM). The TP sensor has a 5.0 volt reference, a ground, and a signal circuit. The signal voltage varies from below 1 volt at closed throttle to about 4 volts at wide open throttle (WOT).
Conditions for Running the DTC
| • | No TP or MAP sensor DTCs set. |
| • | Engine running for at least 3 minutes. |
| • | MAP is below 50 kPa to check for a fixed high TP sensor input. |
| • | MAP is above 70 kPa to check for a fixed low TP sensor input |
| • | MAP steady within 5 kPa. |
| • | IAC Position is between 0 and 130 counts. |
| • | Throttle angle is steady. |
Conditions for Setting the DTC
| • | Predicted Throttle angle is not close to actual throttle angle. |
| • | The above conditions are present for longer than 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A last test failed (current DTC) clears when the diagnostic runs and does not fail. |
| • | A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | Use a scan tool in order to clear the MIL/DTC. |
| • | Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) Description , Clearing Diagnostic Trouble Codes. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
Check for the following conditions:
| • | Damaged or sticking throttle plate or IAC valve. A throttle plate or IAC valve that allows too much airflow while the throttle should be closed may cause a high idle and DTC P0121 to be set. Refer to Idle Air Control System Check for diagnosis. |
| • | Skewed MAP signal or malfunctioning 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. |
If DTC P0121 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.
If the problem is intermittent, refer to Intermittent Conditions .
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
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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 set. With the key On and the engine Off, MAP should indicate the local barometric pressure.
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TP Angle should be near 0% at closed throttle and 100% at WOT and increase smoothly as the throttle is slowly opened. If TP Angle is not indicating closed throttle with no pressure on the accelerator pedal, check for a sticking or binding mechanism and correct as neccessary. If a spike or dropout occurs while sweeping the TP sensor through its operating range, check the connections at the sensor. If the connections are OK replace the sensor.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
|
Important: If any of the following DTCs are set, diagnose these DTCs first: Observe the MAP reading on scan tool with the key On and the engine Off. Is the MAP reading less than the specified value? | 65 kPa | |||||||||
3 |
Did the MAP sensor value change smoothly through the entire range of the test without any erratic readings? | -- | ||||||||
4 | Apply 20 inches Hg vacuum to the MAP sensor then release the vacuum while observing the scan tool. Is the MAP sensor reading on the scan tool close to the specified value with vacuum applied and then return to barometric pressure when the vacuum is released? | 34 kPa | ||||||||
5 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Is the action complete? | -- | -- | |||||||
Observe the TP Angle reading on the scan tool while slowly opening the throttle. Does TP Angle increase steadily and evenly from closed throttle to wide open throttle? | -- | Refer to Diagnostic Aids. | ||||||||
7 |
Is the TP sensor reading near the specified value? | 0V | ||||||||
8 |
Is the TP sensor reading at the specified value? | 5V | ||||||||
9 | Check the following items:
If a problem is found, repair wiring harness as necessary. Refer to Electrical Diagnosis. Was a problem found and corrected? | -- | ||||||||
10 |
Was a problem found and corrected? | -- | ||||||||
11 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | -- | |||||||
Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming Is the action complete? | -- | -- | ||||||||
13 |
Does the scan tool indicate that this test ran and passed? | -- | ||||||||
14 | Review Captured Info using the scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to the applicable DTC table
| System OK |
