For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The throttle position (TP) sensor circuit provides a voltage signal that changes relative to throttle blade angle. The signal voltage will vary from less than 1.0 volt at closed throttle to more than 4.0 volts at Wide Open Throttle (WOT).

When the MAP reading is less than 50 kPa the diagnostic checks for a skewed high TP sensor. When the MAP reading is more than 70 kPa the diagnostic checks for a skewed low TP sensor. If the powertrain control module (PCM) detects an out of range condition, DTC P0121 will be set. The diagnostic will not run when MAP is between 50 kPa-70 kPa.

### Conditions for Running the DTC

• | There is no active TP sensor circuit or MAP sensor DTC.

• | The engine is running for more than 2 minutes.

• | The ECT sensor temperature is above 75°C (167° F).

• | The MAP reading is below 50 kPa for a TP sensor skewed high.

• | The MAP reading is above 70 kPa for a TP sensor skewed low.

• | The MAP is steady for 5 seconds or more.

### Conditions for Setting the DTC

• | The TP sensor reading is above the predicted value when the MAP is below 50 kPa.

• | The TP sensor reading is below the predicted value when the MAP is above 70 kPa.

• | The above conditions are present for 10 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.

• | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using a scan tool.

### Diagnostic Aids

Inspect for a skewed MAP signal or faulty MAP sensor--A skewed MAP signal may cause the PCM to incorrectly determine the TP sensor is out of range.

Inspect for an unusually low or high MAP reading. Refer to Manifold Absolute Pressure Sensor Circuit Diagnosis .

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

• | Loose terminal connection

- | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. 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 | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Important : If any other DTCs are set, diagnose the other DTCs first.

1. Turn ON the ignition, with the engine OFF.
2. Observe the TP Angle reading on the scan tool while slowly opening the throttle.

Does the TP Angle increase steadily and evenly from the Closed Throttle value to the Wide Open Throttle value?

• | Closed Throttle value is the first value.

• | Wide Open Throttle value is the second value.

0%

100%

Go to Step 3

Go to Step 4

3 |

1. Review the Freeze Frame and/or Failure Records data for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame and/or Failure Records data that you observed.

Does the DTC reset?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the TP sensor.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe the TP voltage parameter.

Does the scan tool indicate that the TP voltage parameter is near the specified value?

0.0V

Go to Step 5

Go to Step 6

5 |

1. Turn OFF the ignition.
2. Connect a 3 amp fused jumper wire between the 5 volt reference circuit of the TP sensor and the signal circuit of the TP sensor.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe the TP voltage parameter.

Does the scan tool indicate that the TP voltage parameter is at the specified value?

5.0V

Go to Step 9

Go to Step 7

6 | Test the signal circuit of the TP sensor for a short to voltage. Refer to Wiring Repairs in Wiring Systems . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
7 | Test the 5 volt reference circuit of the TP sensor for high resistance, or a faulty connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8
8 | Test the signal circuit of the TP sensor for high resistance, or a faulty connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
9 | Test the ground circuit of the TP sensor for high resistance, or a faulty connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
10 | Inspect for faulty connections at the harness connector of 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 13 | Go to Step 11
11 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 13 | --
13 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

System OK

Go to Step 2