GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC P1516

Circuit Description

The predicted throttle position (TP), based on accelerator pedal position (APP) and possibly other limiting factors, is compared to the actual TP. The two values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the throttle actuator control (TAC) module redundantly monitor the predicted and actual TP. This diagnostic trouble code (DTC) sets if the PCM detects an out of range condition between the predicted and actual TP.

Conditions for Running the DTC
    • DTC P1518 is not set.
    • The ignition is in the crank or run position.
    • The ignition voltage is greater than 5.23 volts.
    • The TAC system is not in the battery saver mode.

Conditions for Setting the DTC
    • The TAC module detects that the predicted and actual TP are not within a calibrated range of each other or the PCM and the TAC cannot determine TP or both TP sensors are invalid.
    • All of the above conditions are met 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. When this occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.
    • Ensure that the starting and charging systems are operating properly. Low system voltage can cause this DTC to set.
    • 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 run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture Info.
    • For an intermittent, refer to Intermittent Conditions .

Test Description

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

  1. If the TP indicated angle does not follow the movement of the throttle blade, and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or the TP sensor.

    2.

  2. 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 run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture Info.

DTC P1516 - Commanded vs. Actual Throttle Position Performance (TAC)

Step

Action

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

Are DTCs P1518 and P1221 both set also?

Go to DTC P1518

Go to Step 3

3

Is DTC P1221 set?

Go to DTC P1221

Go to Step 4

4
  1. Turn OFF the ignition for 15 seconds.
  2. Turn ON the ignition, with the engine OFF.
  3. Use a scan tool in order to observe the TP sensor 1 and TP sensor 2 angle parameters.
  4. Slowly depress the accelerator pedal to wide open throttle (WOT) and slowly return it to the released position.

Does the scan tool indicate both angle parameters increasing as the pedal is depressed to WOT and decreasing as the pedal is released?

Go to Diagnostic Aids

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the throttle actuator motor harness connector.
  3. Remove the air inlet duct from the throttle body.
  4. Inspect the throttle body and throttle plate for debris, damage, and tampering that could cause the throttle plate to bind. If debris is found, clean the throttle body and repair the source of contamination. If the throttle body and/or throttle plate is damaged, replace the throttle body. Refer to Throttle Body Assembly Replacement .

Did you find and correct the condition?

Go to Step 17

Go to Step 6

6

Using your hand, slowly open the throttle plate to WOT and back to the closed position several times.

Does the throttle plate move smoothly without binding in both directions?

Go to Step 7

Go to Step 14

7

  1. Turn ON the ignition, with the engine OFF.
  2. Using your hand, slowly open the throttle blade to WOT and then to the closed throttle position while observing the TP sensor 1 and TP sensor  2 angle parameters on the scan tool.

Does the scan tool indicate both angle parameters increasing as the throttle blade is moved to WOT and decreasing as it is moved to the closed position?

Go to Step 8

Go to Step 15

8
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the TAC motor circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. Use a DMM in order to test the TAC motor circuits 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 17

Go to Step 9

9

Use a DMM in order to test each TAC motor 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 17

Go to Step 10

10

Use a DMM in order to test each TAC motor 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 17

Go to Step 11

11
  1. Disconnect the other TAC module harness connector.
  2. Use a DMM in order to test for a short between each TAC motor 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 17

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Reconnect the TAC module.
  3. Connect a test lamp between the two TAC motor terminals at the TAC motor harness connector.
  4. Turn ON the ignition, with the engine OFF and observe the test lamp.

Did the test lamp illuminate briefly when the ignition was turned ON?

Go to Step 13

Go to Step 15

13

Inspect for poor connections at the TAC motor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 14

14

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

Did you complete the replacement?

Go to Step 15

--

15

Inspect for poor connections at the TAC module harness connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 16

16

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

Did you complete the replacement?

Go to Step 17

--

17
  1. Use a 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 18

Go to Step 2

18

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

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

Go to Diagnostic Trouble Code (DTC) List

System OK