Refer to Engine Controls Schematics
A/C Pressure Switch, TPS, MAP, ECT and IAT
.
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 throttle position (TP) or manifold absolute pressure (MAP) sensor DTCs are set. |
| • | The engine has been running for at least 3 minutes. |
| • | The MAP is below 50 kPa (7.25 psi) to check for a fixed high TP sensor input. |
| • | The MAP is more than 70 kPa (10.152 psi) to check for a fixed low TP sensor input |
| • | The MAP is steady within 5 kPa (0.725 psi). |
| • | The idle air control (IAC) position is between 0-130 counts. |
| • | The throttle angle is steady. |
Conditions for Setting the DTC
| • | The predicted throttle angle is not close to the 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 3 consecutive drive trips during which the diagnostic runs and passes. |
| • | A last test failed, or the current DTC, clears when the diagnostic runs and passes. |
| • | A History DTC clears after 40 consecutive warm-up cycles, if no other emission related diagnostic failures are reported. |
| • | Use a scan tool in order to clear the MIL diagnostic trouble code. |
| • | Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module 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:
| • | A damaged or sticking throttle plate or IAC valve--A throttle plate or IAC valve that allows too much airflow when the throttle should be closed may cause a high idle and DTC P0121 may set. Refer to Idle Air Control (IAC) System Diagnosis for diagnosis. |
| • | A 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
Numbers below refer to the step numbers on the diagnostic table:
-
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 ignition On and the engine Off, the MAP should indicate the local barometric pressure.
-
The TP Angle should be near 0 percent at closed throttle and near 100 percent at wide open throttle (WOT) and increase smoothly as the throttle is slowly opened. If the TP Angle does not indicate closed throttle when there is 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.
-
This vehicle is equipped with a PCM that utilizes an electrically erasable programmable read only memory (EEPROM). If the PCM is 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 the scan tool with the key in the ON position and the engine Off. Is the MAP reading less than the specified value? | 65 kPa (9.427 psi) | |||||||||
3 |
Did the MAP sensor value change smoothly through the entire range of the test without any erratic readings? | -- | ||||||||
4 | Apply 20 in Hg vacuum to the MAP sensor, then release the vacuum while observing the scan tool. The MAP sensor reading on the scan tool should be close to the specified value with vacuum applied. Does the value return to barometric pressure when the vacuum is released? | 34 kPa (4.93 psi) | ||||||||
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 the TP Angle increase steadily and evenly from closed throttle to wide open throttle (WOT)? | -- | Go to Diagnostic Aids | ||||||||
7 |
Is the TP sensor reading near the specified value? | 0 V | ||||||||
8 |
Is the TP sensor reading at the specified value? | 5 V | ||||||||
9 | Check the following items:
If a problem is found, repair the wiring harness as necessary. Refer to Wiring Repairs in Wiring Systems. 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? | -- | -- | |||||||
|
Important: The replacement PCM must be programmed. Replace the PCM. 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 the Captured Info using the scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
