GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 DTC P1220
Table 1: TP Sensor Position Table

Circuit Description

The throttle position (TP) sensor is mounted on the throttle body assembly. The sensor is actually 2 individual TP sensors within 1 housing. Two separate signal, low-reference and 5-volt reference circuits are used to connect the TP sensor assembly to the throttle actuator control (TAC) module. The 2 sensors have opposite functionality.

TP sensor 1 and accelerator pedal position (APP) sensor 1 share a 5-volt reference circuit that are connected within the TAC module. TP sensor 2 and APP sensor 2 share a 5-volt reference circuit that are connected within the TAC module. If an out of range condition is detected with the TP sensor 2, this DTC will set and the Reduced Engine Power message will be displayed.

The table below shows the percentage and voltage readings of the scan tool based on the position of the TP.

TP Sensor Position Table

TP Sensor

Actual Throttle Plate Position

% Open as Observed on a Scan Tool

Voltage as Observed on a Scan Tool

1

Closed

0

Below 1.0

1

Open

100

Above 3.5

2

Closed

0

Above 3.5

2

Open

100

Below 1.0

Conditions for Running the DTC
    • DTCs P1517, or P1518 are not set.
    • The ignition switch in the crank or run position.
    • The ignition voltage is greater than 5.23 volts.

Conditions for Setting the DTC
    • The TP sensor 2 voltage is less than 0.13 volt or greater than 4.87 volts.
    • All above conditions present for less 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. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing.
    • When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.
    • If this DTC is determined to be intermittent, refer to Intermittent Conditions .

Test Description

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

  1. Using a test lamp reduces the amount of current fed into the signal circuit. The scan tool should display the maximum value for this parameter, 5 volts, even though the actual voltage is higher.

    2.

  2. The TP 2 sensor and the APP 2 sensor share a common 5-volt reference. The 5-volt reference circuits are connected internally within the TAC module. Disconnecting the TAC module will isolate the 5-volt reference circuits.

    3.

  3. The TP sensor 2 and the APP sensor 2 share a common 5-volt reference. A short to voltage on the APP sensor 2, 5-volt reference circuit will affect the TP sensor 2, 5-volt reference circuit.

    4.

  4. When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is DTCs P1515, P1516, or P1518 also set?

--

Go to Diagnostic Trouble Code (DTC) List

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. Close the throttle blade completely by hand while observing the TP sensor 2 voltage parameter on the scan tool.

Does the scan tool indicate TP sensor 2 voltage within the specified values?

4.3-4.8 V

Go to Step 4

Go to Step 7

4

Open the throttle blade to wide open throttle (WOT) by hand while observing the TP sensor 2 voltage parameter on the scan tool.

Does the scan tool indicate TP sensor 2 voltage within the specified values?

0.13-1 V

Go to Step 5

Go to Step 7

5
  1. Turn OFF the ignition for 15 seconds.
  2. Reconnect the throttle actuator motor harness connector.
  3. Reinstall the air inlet duct.
  4. Turn ON the ignition, with the engine OFF.
  5. Select the DTC Info. option on the scan tool.
  6. 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 Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 33

Go to Step 6

6
  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 26

Go to Diagnostic Aids

7

With a scan tool, observe the TP sensor 2 voltage Parameter.

Does the scan tool indicate TP sensor 2 voltage at the specified value?

5 V

Go to Step 8

Go to Step 12

8

Disconnect the TP sensor harness connector.

Does the scan tool indicate TP sensor 2 voltage at the specified value?

0 V

Go to Step 9

Go to Step 13

9
  1. Disconnect the APP sensor harness connector.
  2. Turn ON the ignition, with the engine OFF.
  3. With a DMM, test the TP sensor 2, 5-volt reference circuit for voltage.

Does the DMM indicate voltage near the specified value?

5 V

Go to Step 10

Go to Step 18

10

With a DMM connected between the TP sensor 1 low-reference circuit, and the TP sensor 2 low-reference circuit at the TP sensor harness connector, test for resistance.

Does the DMM indicate resistance within the specified values?

0-5 ohms

Go to Step 14

Go to Step 11

11
  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 2 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 33

Go to Step 30

12

  1. Disconnect the TP sensor harness connector.
  2. Connect a test lamp between the TP sensor 2 signal circuit and B+.

Does the scan tool indicate TP sensor 2 voltage near the specified value?

5 V

Go to Step 20

Go to Step 15

13
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the TP sensor circuits.
  3. Turn ON the ignition.
  4. With a DMM, test the TP sensor 2 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 33

Go to Step 17

14
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP sensor circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. With a DMM, test the APP sensor 2 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 33

Go to Step 24

15
  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 2 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 33

Go to Step 16

16

With a DMM, test the TP sensor 2 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 33

Go to Step 17

17

With a DMM, test for a short between the TP sensor 2 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 33

Go to Step 30

18

  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 2, 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 33

Go to Step 19

19

  1. Turn OFF the ignition.
  2. Disconnect the other TAC module harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. With a DMM, test the APP sensor 2, 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 33

Go to Step 24

20
  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 2, 5-volt 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 33

Go to Step 21

21

With a DMM, test the TP sensor 2, 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 33

Go to Step 22

22
  1. Disconnect the APP sensor harness connector.
  2. Disconnect the other TAC module harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. With a DMM, test the APP sensor 2 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 33

Go to Step 23

23

With a DMM, test the APP sensor 2, 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 33

Go to Step 24

24

With a DMM, test the TP sensor 2, 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 33

Go to Step 25

25

With a DMM, test for a short between the TP sensor 2, 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 33

Go to Step 26

26

With a DMM, test for a short between the APP sensor 2, 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 33

Go to Step 27

27

With a DMM, test the TP sensor 2 signal circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 33

Go to Step 28

28

With a DMM, test the TP sensor 2 low-reference circuit for resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 33

Go to Step 29

29

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 33

Go to Step 31

30

Inspect for poor connections 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 33

Go to Step 32

31

Important: The throttle body and the throttle position sensor assembly should be replaced as a unit. Driveability concerns may result if either is replaced individually.

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

Did you complete the replacement?

--

Go to Step 33

--

32

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

Did you complete the replacement?

--

Go to Step 33

--

33
  1. Use the scan tool in order 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 as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 34

Go to Step 2

34

With a scan tool, observe the stored information in Capture Info.

Does the scan tool indicate any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK