Circuit Description
The DTC P0120 Throttle Position (TP) Sensor Circuit diagnostic detects an out of range sensor signal. The 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.
Throttle Opening | TP Resistance | TP Percentage | TP Signal Voltage |
|---|---|---|---|
Large | High | High | High |
Small | Low | Low | Low |
Conditions for Running the DTC
| • | The ignition is ON. |
| • | DTC P0120 runs continuously once the above condition has been met. |
Conditions for Setting the DTC
| • | The TP sensor input to the PCM is less than 0.1 volt for more than 5 seconds. |
| OR |
| • | The TP sensor input to the PCM is more than 4.9 volts for more than 5 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 TP sensor angle will default to 0 percent. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run, and the fault condition is no longer present. |
| • | A DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
If DTCs P0110, P0115, and P0120 are also set, the malfunction may be in the sensor ground circuit.
On a good TP sensor the scan tool 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 TP sensor 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 in Wiring Systems.
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.
-
The Diagnostic System Check-Engine Controls 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.
-
This step determines if DTC P0120 is the result of a hard failure or an intermittent condition.
-
When the 5-volt reference is jumpered to the TP input circuit, the scan tool parameter should read 99 percent.
-
When the TP sensor 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 | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | 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 to 11% | 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 P0110 or DTC P0115 also set? | -- | Go to Step 13 | Go to Step 5 |
5 | Observe the TP sensor with the throttle closed. Is the TP sensor percentage near 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% | |||
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? | -- | ||
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 15 | |
12 |
Did you find and repair a condition? | -- | Go to Step 19 | |
13 |
Did you find and repair a condition? | -- | Go to Step 18 | |
14 |
Did you find and repair a condition? | -- | Go to Step 18 | |
15 | Repair the open in the TP sensor ground circuit between the sensor and SP108. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
16 |
Did you find and repair a condition? | -- | Go to Step 17 | |
17 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | -- | |
18 |
Did you find and repair a condition? | -- | ||
19 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | -- | |
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 | |
