GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The throttle position (TP) sensor incorporates 2 ratiometric TP sensors into one housing. TP sensor 1 and TP sensor 2 each have a 5-volt reference circuit supplied by the throttle actuator control (TAC) module. The TAC module supplies each TP sensor with a low reference circuit. Each TP sensor supplies the TAC module with a signal voltage that is proportional to the throttle blade position. The TP signal voltages are opposite from one another. TP sensor 1 is pulled up to reference voltage as the throttle blade is opened. The TP sensor 2 is pulled down to low reference as the throttle blade is opened. The TP sensor 1 and the accelerator pedal position (APP) sensor 1 share a 5-volt reference circuit that is bussed within the TAC module. The TP sensor 2 and the APP sensor 2 share a 5-volt reference circuit that is also bussed within the TAC module. The APP sensor 3 has a dedicated 5-volt reference circuit.

When this DTC sets, the Reduced Engine Power indicator will be displayed.

This DTC incorporates 3 different diagnostic tests:

    • TP sensor 1 signal circuit voltage out of range
    • Throttle blade minimum position for the TP sensor 1 out of range
    • 5-volt reference of the TP sensor 1 voltage out of range

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0120 Throttle Position (TP) Sensor 1 Circuit

Conditions for Running the DTC

    • DTCs P2108 or U0107 are not set.
    • The ignition switch is in the crank or in the run position.
    • The ignition voltage greater than 5.23 volts.
    • The TP sensor 1 signal voltage test runs continuously once the above conditions are met.
    • The throttle blade minimum position for the TP sensor 1 test runs once when the ignition is turned ON and the above conditions are met.
    • The 5-volt reference of the TP sensor 1 voltage test runs continuously once the above conditions are met.

Conditions for Setting the DTC

    • TP sensor 1 signal voltage is less than 0.38 volts or more than 4.50 volts for more than 0.1 second.
        OR
    • The TP sensor 1 minimum throttle blade position is less than 0.38 volts or more than 0.71  volts for less than 1 second.
        OR
    • The 5-volt reference circuit of the TP sensor 1 is shorted to ground for more than 0.01 second.
        OR
    • The 5-volt reference circuit of the TP sensor 1 is less than 4.54 volts or more than 5.21 volts for more than 1 second.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
    • The control module commands the TAC system to operate in the Reduced Engine Power mode.
    • A message center or an indicator displays Reduced Engine Power.
    • Under certain conditions the control module commands the engine OFF.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

    • Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no DTC circuit or component conditions found during diagnostic testing.
    • When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting the components during testing may set additional DTCs. Keep this in mind when reviewing the Capture info.
    • If this DTC is determined to be intermittent, refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

  1. When the TAC module detects a condition within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting the components during testing may set additional DTCs. Keep this in mind when reviewing the Capture Info.

Step

Action

Values

Yes

No

Schematic References: Engine Controls Schematics

Connector End View References: Powertrain Control Module Connector End Views , or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Is DTC  P1516, or U0107 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Remove the air inlet duct from the throttle body assembly.
  3. Disconnect the throttle actuator motor harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Manually close the throttle blade completely while observing the throttle position (TP) sensor 1 voltage on the scan tool.

Does the scan tool indicate TP sensor 1 voltage within the specified values?

0.38-0.71 V

Go to Step 4

Go to Step 8

4

Manually open the throttle blade to wide open throttle (WOT) while observing the TP sensor 1 voltage parameter on the scan tool.

Does the scan tool indicate that the TP sensor 1 voltage is within the specified values?

4.09-4.87 V

Go to Step 5

Go to Step 8

5

  1. Disconnect the TP sensor harness connector.
  2. Disconnect the throttle actuator control (TAC) module harness connector containing the TP sensor circuits.
  3. With a DMM, test the TP sensor low reference circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 6

6

  1. Turn OFF the ignition for 15 seconds.
  2. Reconnect the TAC module harness connector.
  3. Reconnect the throttle actuator motor harness connector.
  4. Reinstall the air inlet duct.
  5. Turn ON the ignition, with the engine OFF.
  6. Select the DTC Info on the scan tool.
  7. Lightly touch and move the related engine wiring harnesses and connectors for the TP sensor while observing the DTC Info. The DTC will set if an intermittent condition is present. Refer to Connector Repairs and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 7

7

  1. Continue to observe DTC Info.
  2. Slowly depress the accelerator pedal to WOT, and then slowly return the pedal to the released position 3 times.

Does the scan tool indicate this DTC failed this ignition?

--

Go to Step 27

Go to Diagnostic Aids

8

  1. Disconnect the TP sensor harness connector.
  2. Measure voltage at the TP sensor 1 signal circuit with a DMM connected to ground.

Does the DMM indicate voltage within the specified values?

3.94-6.06 V

Go to Step 13

Go to Step 9

9

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the TP sensor circuits.
  3. Turn ON the ignition with the engine OFF.
  4. With a DMM, test the TP sensor 1 signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 10

10

With a DMM, test the TP sensor 1 signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 11

11

With a DMM, test the TP sensor 1 signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 12

12

  1. Disconnect the other TAC module harness connector.
  2. With a DMM, test for a short between the TP sensor 1 signal circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 28

13

With a DMM, test the TP sensor 1, 5-volt reference circuit for voltage.

Does the DMM indicate voltage within the specified values?

3.94-6.06 V

Go to Step 23

Go to Step 14

14

Does the DMM indicate voltage greater than the specified value?

6.06 V

Go to Step 15

Go to Step 17

15

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the TP sensor circuits.
  3. Turn ON the ignition with the engine OFF.
  4. With a DMM, test the TP sensor 1 5-volt reference circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 16

16

  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor harness connector.
  3. Disconnect the other TAC module harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. With a DMM, test the APP sensor 1 5-volt reference circuit for a short to voltage . Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 21

17

Disconnect the APP sensor.

Does the DMM indicate voltage less than the specified value?

3.94 V

Go to Step 18

Go to Step 30

18

  1. Disconnect the TAC module harness connector containing the TP sensor circuits.
  2. With a DMM, test the TP sensor 1 5-volt reference circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 19

19

With a DMM, test the TP sensor 1 5-volt reference circuit for a short to ground.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 20

20

With a DMM, test the APP sensor 1 5-volt reference circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 21

21

With a DMM, test for a short between the TP sensor 1 5-volt reference circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 22

22

With a DMM, test for a short between the APP sensor 1 5-volt reference circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 28

23

  1. Disconnect the TAC module connector containing the TP sensor circuits.
  2. With a DMM, test the TP sensor 1 signal circuit for a short to any other TP sensor circuit. If a short is found refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 24

24

  1. Reconnect the TAC module harness connector containing the TP sensor circuits.
  2. Connect a fused jumper between the TP sensor 1 low reference circuit and the TP sensor 1 signal circuit.
  3. With a scan tool, observe the TP sensor 1 voltage parameter.

Does the scan tool indicate voltage near the specified value?

0 V

Go to Step 26

Go to Step 25

25

  1. Turn OFF the ignition.
  2. Disconnect the TAC Module harness connector containing the TP sensor circuits.
  3. With a DMM, test the TP sensor 1 low reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 28

26

Inspect for poor connections at the TP sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 29

27

Inspect for poor connections at the APP module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 30

28

Inspect for a poor connection at the TAC Module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 32

Go to Step 31

29

Important: The throttle position sensor is not a serviceable part and should only be replaced with the throttle body assembly.

Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .

Did you complete the replacement?

--

Go to Step 32

--

30

Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 32

--

31

Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement .

Did you complete the replacement?

--

Go to Step 32

--

32

  1. Use the scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze/Frame Failure Records.

Does the DTC run and pass?

--

Go to Step 33

Go to Step 2

33

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK