For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The PCM supplies a 5.0 V reference signal and a ground to the Throttle Position (TP) sensor. The TP sensor sends a voltage signal back to the PCM relative to the throttle plate opening. The voltage signal will vary from approximately 0.35 V at closed throttle, to over 4.65 V at wide open throttle. The PCM can detect if the TP sensor is out of the above range while cruising by waiting for a Manifold Air Pressure (MAP) change and then checks if the TP sensor has also changed as expected by calculating what the TP signal should be at a given RPM and engine load. During idle conditions, the PCM verifies that the engine is stable and at idle, and ensures that the TP signal is below a given percent.

### Conditions for Setting the DTC

DTCs P0106, P0107, P0108, P0171, P0172, P0200, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0404, P0405, P0440, P0442, P0452, P0453, P0502, P0506, P0507, P0601, P0602, P1441 not set.

TP angle is greater than 7% at idle after attempting to auto-zero.

• | Engine run time is greater than 20 seconds.

• | Engine Coolant Temperature (ECT) is greater than 20°C (68°F).

• | TP is stable ± 2%.

• | MAP is less than 37 kPa.

And

TP angle is greater than the following specified percentages at the given RPMs for at least 6 seconds.

• | TP angle is greater than 2% at 0 RPM

• | TP angle is greater than 10% at 800 RPM

• | TP angle is greater than 20% at 1600 RPM

• | TP angle is greater than 25% at 2400 RPM

• | TP angle is greater than 30% at 3200 RPM

• | TP angle is greater than 35% at 4000 RPM

• | TP angle is greater than 35% at 4800 RPM

• | TP angle is greater than 40% at 5600 RPM

• | TP angle is greater than 40% at 6400 RPM

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM will record the operating conditions at the time that the diagnostic fails. This information stores in the Freeze Frame and Failure Records buffers.

• | A history DTC stores.

• | The coolant fan turns ON.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | The MIL/DTCs can be cleared by using the scan tool.

### Diagnostic Aids

• | A TP sensor that is stuck will attempt an auto zero every time that the engine runs. An indication of this happening would be the TP sensor percentage will be 0 percent and the TP sensor voltage will be high.

• | Using a DMM in order to check the TP sensor 5 volt reference circuits may not detect small amounts of resistance. Connecting a jumper wire from the TP sensor 5 volt reference circuit to the TP sensor signal circuit is a better test in this situation.

• | Certain conditions can produce normal results when probed, but can cause a bad reading when connected. Check for the following conditions on the TP sensor electrical connectors:

• | Spread terminals

• | Poor electrical terminal connections

• | If a DTC P0121 cannot be duplicated, the information included in the Freeze Frame/Failure Records data can be useful. Use the scan tool DTC information data in order to determine the status of the DTC.

### Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

2. Disconnecting the EGR valve and relating sensors (that all use the internal 5 volt reference circuit of the PCM) can determine if the 5 volt reference circuit is shorted or if one of the relating sensors is causing a short on the 5 volt reference circuit.

3. The TP sensor has an auto zeroing feature. If the voltage reading is between 0.2 to 0.9 volts, the PCM will assume that the TP sensor is at a closed throttle position (0 percent). If the reading is out of the auto zeroing range at closed throttle, look for a binding or a damaged linkage.

4. The TP sensor may be able to auto zero itself after several engine start ups if the TP sensor is stuck, but may not be able to reach its range near 100 percent. The TP sensor angle should increase steadily. If the TP sensor voltage value spikes high or low, consider the test failed.

5. By disconnecting the TP sensor electrical connector the scan tool should display a voltage near zero volts.

6. A short to voltage on the signal circuit would most likely be caused by the 5 volt reference circuit. Check for the 5 volt reference circuit being pinched with the signal circuit.

7. Electrical terminal that are spread out or poor electrical terminal connections can produce normal results when the terminals are probed, but can cause abnormal readings when the electrical connector is connected. Be sure to check all the electrical terminals for this conditions.

8. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming and Crankshaft Position System Variation Learn .

9. If no malfunctions have been found at this point and no additional DTCs were set, refer to the Diagnostic Aids for additional checks and information.

#### DTC P0121 - Throttle Position (TP) Sensor System Performance

Step | Action | Value(s) | 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 |

1. Turn ON the ignition switch leaving the engine OFF.
2. Install a scan tool.
3. Check for DTCs with the scan tool.

Are any of the following DTCs set or last test failed on the scan tool?

• | EGR

• | A/C

• | Fuel tank pressure sensor

--

Go to the applicable DTC table

Go to Step 3

3 |

1. Throttle fully closed.
2. Check the TP sensor voltage reading with the scan tool. The TP sensor voltage should be less than the specified value.

Is the TP sensor voltage less than the specified value?

0.90V

Go to Step 4

Go to Step 6

4 |

1. Select the TP angle parameter on the scan tool.
2. Monitor the scan tool while depressing the accelerator pedal to the floor and then slowly release the pedal (repeat the procedure several times).

Does the TP angle value increase steadily to greater than the first specified value and does the TP angle value decrease steadily to less than the second specified value?

98%

1%

Go to Step 5

Go to Step 6

5 |

1. Review the Freeze Frame data and record the parameters.
2. Start the engine.
3. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting the DTC as specified.

Is the TP angle greater than the specified value in the Conditions For Running The DTC when the engine is running near the associated RPM?

--

Go to Step 6

Go to Step 16

6 |

1. Turn OFF the ignition switch.
2. Disconnect the TP sensor electrical connector.
3. Turn ON the ignition switch leaving the engine OFF.

Is the TP sensor voltage approximately near the specified value?

0.0 V

Go to Step 7

Go to Step 8

7 | Connect a fused jumper wire between the following TP sensor electrical connector circuit terminals:

• | 5 volt reference circuit

• | Signal circuit

Is the TP sensor voltage approximately near the specified value on the scan tool?

5.0 V

Go to Step 9

Go to Step 10

8 | Check for a short to voltage on the TP sensor signal circuit. Was a problem found? | -- | Go to Step 16 | Go to Step 15
9 | Connect a test light between B+ and the TP sensor ground electrical terminal. Does the test light illuminate? | -- | Go to Step 11 | Go to Step 12
10 |

1. Check the TP sensor 5 volt reference and the signal circuits for the following conditions:

• | Poor electrical terminal tension

• | Poor electrical terminal connection(s)

2. Repair the conditions as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 16

Go to Step 13

11 |

1. Check the TP sensor electrical connector for the following conditions:

• | Poor electrical terminal tension

• | Poor electrical terminal connection(s)

2. Repair the conditions as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 16

Go to Step 14

12 |

1. Check the TP sensor ground circuit at the PCM electrical connector for the following conditions:

• | Poor electrical terminal tension

• | Poor electrical terminal connection

2. Repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 16

Go to Step 15

13 |

1. Check for the following conditions in PCM electrical connectors:

• | Poor electrical connection

• | Resistance in the electrical connector connection

2. Repair the PCM electrical connector conditions as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 16

Go to Step 15

14 |

1. Turn OFF the ignition switch.
2. Replace the TP sensor. Refer to the Throttle Position Sensor Replacement .

Is the action complete?

--

Go to Step 16

--

15 | Replace the PCM. Refer to the Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 16 | --
16 |

1. Clear the DTCs with the scan tool.
2. Start the engine.
3. Allow the engine to idle at the normal operating temperature.
4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 17

Go to Step 2

17 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK