Circuit Description
The throttle position (TP) sensor is used by the powertrain control module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits:
| • | A 5-volt reference circuit |
| • | A low reference circuit |
| • | A TP signal circuit |
The PCM provides the TP sensor with 5 volts on the 5-volt reference circuit and a ground on the low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the wide open throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to greater than 4 volts through the TP sensor signal circuit. When the conditions for running this DTC are met, the PCM will use the manifold absolute pressure (MAP) sensor to determine if the predicted operating range of the TP sensor is correct. If the PCM detects the TP sensor voltage is out of the predicted range, DTC P0121 sets.
Conditions for Running the DTC
| • | DTCs P0107, P0108, P0122, P0123 are not set. |
| • | The engine is running for more than 2 minutes. |
| • | The engine coolant temperature (ECT) is more than 75°C (167°F). |
| • | The MAP reading is less than 50 kPa for a TP sensor skewed high test. |
| • | The MAP reading is more than 70 kPa for a TP sensor skewed low test. |
| • | The MAP is steady for 5 seconds or more. |
Conditions for Setting the DTC
| • | The PCM detects that the TP sensor voltage is more than the predicted value when the MAP sensor pressure is less than 50 kPa. |
| OR |
| • | The PCM detects that the TP sensor voltage is less than the predicted value when the MAP sensor pressure is more than 70 kPa. |
| • | The above conditions are met for 5 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
2 | Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 3 | ||||||||
3 |
Important: The vehicle used for the comparison is not limited to the same type of vehicle as is being serviced. A vehicle known to provide an accurate reading is acceptable. Do you have access to another vehicle in which the MAP sensor pressure can be observed with a scan tool? | -- | Go to Step 4 | Go to Step 5 | ||||||||
4 |
Is the difference between the values less than the specified value? | 3 kPa | Go to Step 6 | |||||||||
5 |
Important: The Altitude vs Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or very low or very high temperature may cause a reading to be slightly out of range.
Does the MAP sensor indicate the correct barometric pressure? | -- | Go to Step 6 | |||||||||
6 |
Does the MAP sensor pressure change? | -- | Go to Step 7 | |||||||||
7 |
Is the voltage less than the specified value with the throttle in the closed position? | 0.90 V | Go to Step 8 | Go to Step 9 | ||||||||
8 |
Does the TP sensor parameter increase steadily to more than the first specified value, and then decrease steadily returning to less than the second specified value? | 98% 1% | Go to Intermittent Conditions | Go to Step 10 | ||||||||
9 | Inspect the throttle body for the following conditions:
Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 10 | ||||||||
10 |
Is the voltage less than the specified value? | 0.1 V | Go to Step 11 | Go to Step 15 | ||||||||
11 | Measure the voltage from the 5-volt reference circuit of the TP sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage more than the specified value? | 5.2 V | Go to Step 16 | Go to Step 12 | ||||||||
12 | Probe the 5-volt reference circuit of the TP sensor with a test lamp that is connected to a good ground. Refer to Circuit Testing and Probing Electrical Connectors in Wiring Systems. Is the test lamp OFF? | -- | Go to Step 17 | Go to Step 13 | ||||||||
13 |
Is the voltage more than the specified value? | 4.9 V | Go to Step 14 | Go to Step 18 | ||||||||
14 |
Is the voltage more than the specified value? | 0.2 V | Go to Step 19 | Go to Step 20 | ||||||||
15 |
Important: Disconnecting the powertrain control module (PCM) may eliminate the short during testing. Test the TP sensor signal circuit between the PCM and the TP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 23 | ||||||||
16 |
Important: Disconnecting the PCM may eliminate the short during testing. Test all of the branches of the 5-volt reference circuit that are shared with the TP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 23 | ||||||||
17 | Test the 5-volt reference circuit between the PCM and the TP sensor for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 21 | ||||||||
18 | Test the TP sensor signal circuit between the PCM and the TP sensor for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 21 | ||||||||
19 | Test the low reference circuit between the PCM and the TP sensor for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 21 | ||||||||
20 | Test for an intermittent and for a poor connection at the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 22 | ||||||||
21 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 23 | ||||||||
22 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 24 | -- | ||||||||
23 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 24 | -- | ||||||||
24 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 25 | ||||||||
25 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||
