For 1990-2009 cars
Engine Controls Components
Engine Controls Schematics
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 below 1.0-volt at closed throttle to above 4.0-volts at wide open throttle (WOT).

When the MAP reading is below 50 kPa the diagnostic tests for a skewed high TP sensor. When the MAP reading is above 70 kPa the diagnostic tests for a skewed low TP sensor. If the PCM detects an out of range condition, DTC P0121 will be set. The diagnostic will not run when the MAP is between 50 kPa and 70 kPa.

### Conditions for Running the DTC

• | Active TP sensor circuit or MAP sensor DTC are not present.

• | The engine is running for 2 minutes.

• | The ECT sensor temperature 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 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 a faulty MAP sensor. A skewed MAP signal may cause the PCM to incorrectly determine that the TP sensor is out of range. Monitor the scan tool for an unusually low or high MAP reading. This condition can cause DTC P0121 to be set. 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.

#### DTC P0121 - TP System Performance

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 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 Diagnostic Aids

Go to Step 3

3 |

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?

0V

Go to Step 4

Go to Step 5

4 |

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?

5.0 V

Go to Step 8

Go to Step 6

5 | 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 12 | Go to Step 11
6 | Test the 5-volt reference circuit of the TP sensor for high resistance, or a poor 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 12 | Go to Step 7
7 | Test the signal circuit of the TP sensor for high resistance, or a poor 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 12 | Go to Step 11
8 | Test the ground circuit of the TP sensor for high resistance, or a poor 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 12 | Go to Step 9
9 | Inspect for poor 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 12 | Go to Step 10
10 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
11 | Important: : Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 12 | --
12 |

1. Review and record scan tool Failure Records data.
2. Clear DTCs
3. Operate the vehicle within Failure Records conditions as noted.
4. Using a scan tool, monitor Specific DTC info for DTC P0121.

Does the scan tool indicate DTC P0121 failed this ignition?

--

Go to Step 2

System OK