Circuit Description
The DTC P0120 Throttle Position (TP) Sensor 1 Circuit diagnostic detects an out of range sensor signal. The TP sensor 1 output provides the powertrain control module (PCM) with a signal voltage that is proportional to the throttle plate movement. The TP sensor used with the throttle actuator control (TAC) system is actually a Hall Effect switch. The Hall Effect switch is surrounded by a magnetic yoke that induces a flux in the magnetic field when the throttle shaft is rotated. The PCM provides a 5-volt reference voltage to the sensor circuits in the TAC module. An integrated circuit (IC) receives and converts the magnetic pulses into two separate TP signal, each with their own characteristics. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens. TP sensor 1 determines the actual throttle valve position. TP sensor 2 has a voltage that is more than twice that of TP sensor 1 at idle. TP sensor 2 provides a backup value for TP sensor 1.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0120 Throttle Position (TP) Sensor 1 Circuit
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | DTC P0120 runs continuously once the above condition has been met. |
Conditions for Setting the DTC
| • | The TP sensor 1 input to the PCM is less than 0.2 volt. |
| OR |
| • | The TP sensor 1 input to the PCM is more than 4.5 volts. |
| • | Either of the above conditions is present for at least 2 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM stores the conditions that were present when the DTC set as Freeze Frame data. |
| • | The engine will operate in the reduced power mode and the TP sensor angle will default to 19 percent. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip in which the diagnostic runs without a fault. |
| • | The PCM clears a History DTC after 40 consecutive warm-up cycles without a fault. |
| • | You use the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | On the scan tool a good TP sensor 1 will typically display a TP angle of 8-10 percent at idle, and 76-77 percent at wide open throttle (WOT). |
| • | An intermittent malfunction may be caused by fault in the TAC module electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions . |
| • | Repair any electrical circuit faults that were found. Refer to Wiring Repairs . |
| • | The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and 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.
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This step determines if DTC P0120 is the result of a hard failure or an intermittent condition.
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When the 5-volt reference is jumpered to the TP sensor 1 input circuit, the scan tool parameter should read 99 percent.
-
When the TP sensor 1 input circuit is jumpered to battery voltage, the scan tool parameter should read 99 percent.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||
With the throttle closed, select the TP sensor parameter on the scan tool. Is the TP sensor percentage within the specified value? | 7-16% | Go to Step 3 | Go to Step 4 | |
3 |
Does DTC P0120 set? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 | Is a DTC P0453 also set? | -- | Go to Step 13 | Go to Step 5 |
5 | Observe the throttle position (TP) sensor with the throttle closed. Is the TP sensor percentage at the specified value? | 99% | Go to Step 10 | Go to Step 6 |
6 | Observe the TP sensor with the throttle closed. Is the TP sensor percentage less than the specified value? | 2% | Go to Step 7 | Go to Diagnostic Aids |
Is the TP sensor percentage more than the specified value? | 90% | Go to Step 16 | Go to Step 8 | |
Is the TP sensor percentage more than the specified value? | 90% | Go to Step 9 | Go to Step 14 | |
9 |
Did you find and repair a condition? | -- | Go to Step 20 | Go to Step 18 |
10 |
Is the TP sensor percentage at the specified value? | 0% | Go to Step 11 | Go to Step 12 |
11 | Connect a test lamp to B+ and the ground circuit of the TP sensor. Did the test lamp illuminate? | -- | Go to Step 17 | Go to Step 15 |
12 |
Did you find and repair a condition? | -- | Go to Step 20 | Go to Step 19 |
13 |
Did you find and repair a condition? | -- | Go to Step 20 | Go to Step 18 |
14 |
Did you find and repair a condition? | -- | Go to Step 20 | Go to Step 18 |
15 | Repair the open in the TP sensor 1 ground circuit between the TAC module and SP108. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 20 | -- |
16 |
Did you find and repair a condition? | -- | Go to Step 20 | Go to Step 17 |
17 | The TP sensor in the TAC module is faulty. Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- |
18 |
Did you find and repair a condition? | -- | Go to Step 20 | Go to Step 19 |
19 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 20 | -- |
20 |
Does the DTC run and pass? | -- | Go to Step 21 | Go to Step 2 |
21 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
