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

### Circuit Description

The PCM supplies a 5V reference signal and a ground to the 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 0.45V at closed throttle, to over 4.5V at wide open throttle. The PCM can detect if the TP sensor is out of 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

DTC(s) P0107, P0108, P0122, P0123 not set.

#### Idle Test

• | The vehicle speed is less than 1 mph

• | The engine speed is less than 1050 RPM

• | The IAC counts are less than 145 counts

• | The Manifold Absolute Pressure (MAP) is stable

and

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

#### Cruise Test

• | The TP is stable ± 2 percent

• | The MAP is less than 37 kPa

and

TP angle is greater than the following specified percentages at the given RPMs.

• | TP angle is greater than 33 percent at 1600 RPM

• | TP angle is greater than 55 percent at 2400 RPM

• | TP angle is greater than 60 percent at 3200 RPM

• | TP angle is greater than 79 percent at 4000 RPM

• | TP angle is greater than 75 percent at 4800 RPM

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will illuminate.

• | 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

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.

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

3. Normal TP voltage when the throttle plates are fully closed is near 0.50V. A sensor will display a higher voltage when the sensor is stuck or a circuit is malfunctiony.

4. A disconnected TP sensor should not display a voltage reading on the scan tool. An amount less than the specified value is normal.

5. When the test light is connected to the ground circuit, the light should glow brightly if the ground circuit may be OK but could have a small amount of resistance in the circuit. The voltmeter is used to detect the small amounts of resistance using the voltage drop method. If the test light glows dimly or not at all, then resistance in the circuit is present and using the voltmeter is not necessary.

6. In order for DTC P0121 to set with a short voltage in the TP signal circuit, the voltage must be minimal enough to not set a DTC P0123, and more than 0.5V.

7. Disconnecting the EGR valve and sensors connected to the 5V reference circuits internally to the PCM determines if the 5V reference circuit is shorted or if one of the sensors is causing a short on the 5V reference circuit.

8. The replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Techline procedure for the PCM reprogramming and also refer to the Powertrain Control Module (PCM) for the Crankshaft variation learn procedure .

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

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

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn the ignition switch ON, with the engine OFF.
2. Install a scan tool.
3. Select the TP angle parameter on the scan tool.
4. 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 when the accelerator pedal is depressed to greater than the specified value and decrease steadily when the pedal is released to less than the specified value?

98% 1%

Go to Step 3

Go to Step 5

3 | Does the scan tool display a TP voltage below the specified value when the throttle is fully closed? | .80V | Go to Step 4 | Go to Step 5
4 |

1. Turn the ignition switch ON, with the engine OFF,
2. Review the Freeze Frame data and note the parameters.
3. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting The DTC as noted.

Is the TP angle vs. RPM value greater than the specified value in theConditions For Setting The DTC ?

--

Go to Step 5

Go to Step 12

5 | Disconnect the TP sensor electrical connector. Is the TP sensor voltage less then the specified value? | 0.5V | Go to Step 6 | Go to Step 7
6 |

1. Connect a test light to the ground circuit and B+ at the TP sensor electrical connector.
2. Connect a voltmeter to the ground circuit and ground.

Does the voltmeter read a voltage greater than the specified value?

.5V

Go to Step 8

Go to Step 9

7 | Check the TP signal circuit for a short to voltage and repair as necessary. Was a repair necessary? | -- | Go to Step 16 | Go to Step 15
8 | Check the TP sensor ground circuit for a poor connection or resistance at the TP sensor connector and repair as necessary. Was a repair necessary? | -- | Go to Step 16 | Go to Step 14
9 | With a DVM connected to ground, probe the 5V reference circuit at the TP sensor connector. Does the DVM display a voltage near the specified value? | 5V | Go to Step 13 | Go to Step 10
10 |

1. Disconnect the EGR valve, MAP, A/C, fuel pressure sensors electrical connectors.
2. Again probe the 5V reference circuit at the TP sensor connector.

Does the DVM display a voltage near the specified value?

5V

Go to Step 11

Go to Step 12

11 |

1. Leaving the DVM connected to the TP 5V reference circuit, reconnect each disconnected component one at a time until the voltage reading displays other than a voltage near the specified value.
2. Replace the component that caused the voltage reading to be other than a voltage near the specified value.

Is the action complete?

5V

Go to Step 16

--

12 | Check for a short to voltage in the 5V reference circuit and repair if necessary. Was a repair necessary? | -- | Go to Step 16 | Go to Step 15
13 | Replace the TP sensor. Is the action complete? | -- | Go to Step 16 | --
14 | Check the PCM electrical connectors for a poor connection or resistance and repair as necessary. Was a repair necessary? | -- | Go to Step 16 | Go to Step 15
15 | Replace the PCM. Is the action complete? | -- | Go to Step 16 | --
16 |

1. Using the scan tool, clear DTCs.
2. Start engine and idle at normal operating temperature.
3. Operate 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 if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK, refer to Diagnostic Aids