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

### Circuit Description

The throttle position (TP) sensor is a potentiometer whose resistance value changes along with the throttle valve position. The powertrain control module (PCM) provides a 5 volt reference voltage to the TP sensor. The PCM reads the voltage across the TP sensor and uses the voltage to calculate the percentage of throttle valve opening. The TP sensor resistance decreases as the throttle valve opening increases. When the TP sensor resistance decreases the voltage being monitored by the PCM increases. The TP sensor resistance increases when the throttle valve opening decreases, therefore the voltage being monitored by the PCM will decrease.

### Condition for Running the DTC

The ignition is ON or the engine is running.

### Conditions for Setting the DTC

• | High TP sensor voltage (TP angle is more than 96 percent) is indicated at the PCM with the engine running.

• | The above condition is present for at least 5 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL).

• | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

• | The PCM enters the Fail-Safe Function and assumes the engine throttle valve angle is 24.5 degrees.

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after three consecutively passing trips without a fault present.

• | A History DTC clears after 40 consecutive warm-up cycles without a fault.

• | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC.

### Diagnostic Aids

If the DTC P0123 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0123 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0123 appears in the Not Ran Since Code Cleared list, the P0123 diagnostic has not yet run. When the DTC P0123 does not appear in the Not Ran Since Code Cleared list, the P0123 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0123 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

An intermittent malfunction may be caused by a fault in the TP sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:

• | Backed out terminals

• | Improper mating of terminals

• | Broken electrical connector locks

• | Improperly formed or damaged terminals

• | Faulty terminal to wire connections

• | Physical damage to the wiring harness

• | A broken wire inside the insulation

• | Corrosion of electrical connections, splices, or terminals

If you cannot duplicate a DTC P0123, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

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

2. The percentage of TP sensor movement should not be more than 99 percent when observing the TP sensor parameter from closed throttle position to wide open throttle.

3. This step checks whether the malfunction that caused the DTC P0123 is still present. Driving the vehicle under these conditions will verify whether the fault is present. After performing the scan tool Clear DTC Information function, the DTC P0123 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0123 appears in the Not Ran Since Code Cleared list, the P0123 diagnostic has not yet run. When the DTC P0123 does not appear in the Not Ran Since Code Cleared list, the P0123 diagnostic has run. If the MIL is NOT ILLUMINATED, and there is no PENDING DTC Status in DTC Information, the P0123 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

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, leaving the engine OFF.
2. Install a scan tool.
3. Observe the TP sensor parameter on the scan tool while you depress the accelerator pedal from the idle position to wide open throttle.

Does the TP sensor percentage steadily increase within the specified value?

0-99%

Go to Step 4

Go to Step 3

3 |

1. Turn ON the ignition, leaving the engine OFF.
2. Perform the scan tool Clear DTC Information function.
3. Operate the vehicle within the Freeze Frame conditions as specified or until the DTC P0123 diagnostic has run. Refer to the Test Description.

Did a DTC P0123 set?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the TP sensor electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage from the 5 volt reference circuit (harness side) with a DMM.

Is the voltage at the specified value?

5.0 volts

Go to Step 5

Go to Step 8

5 | Probe the TP sensor ground circuit at the TP sensor harness connector using a test lamp connected to B+. Did the test lamp illuminate? | -- | Go to Step 6 | Go to Step 10
6 |

1. Turn OFF the ignition.
2. Connect the TP sensor electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Backprobe the TP sensor signal circuit at the PCM with a DMM.

Is the TP sensor signal voltage within the specified value?

0.5-1.0 volts

Go to Step 12

Go to Step 7

7 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Check for a short to voltage on the TP sensor signal circuit.
4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 13

Go to Step 9

8 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Check for a short to voltage on the 5 volt reference circuit.
4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 13

Go to Step 12

9 |

1. Check the TP sensor circuits for poor electrical connections at the sensor and the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 13

Go to Step 11

10 |

1. Test for an open in the TP sensor ground circuit or a faulty ground circuit connection. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 13

Go to Step 12

11 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | Go to Step 13 | --
12 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 13 | --
13 |

1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on the scan tool?

--

Go to Diagnostic Trouble Code (DTC) List

System OK