GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Corvette 🢒 DTC 🢒 DTC P1516

Circuit Description

The predicted throttle position is compared to the actual throttle position. The 2 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 the actual throttle position. This DTC sets if the TAC detects an out of range condition between the predicted and the actual throttle position.

Conditions for Running the DTC
    • DTC P1518 is not set.
    • The ignition switch is in the crank or the 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 throttle positions are not within a calibrated range of each other.
    • OR
        The PCM and the TAC cannot determine throttle position.
    • OR
        Both throttle position (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 water intrusion occurs, multiple DTCs could be set with no DTC 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 1 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 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 1 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 components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

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

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. With a scan tool, observe the TP sensor 1 and the TP sensor 2 angle parameters.
  4. Slowly depress the accelerator pedal to wide open throttle (WOT) and slowly return the pedal 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 the 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

Manually, slowly open the throttle plate to WOT and return the plate 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. Manually, slowly open the throttle blade to WOT and return the plate 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 the throttle blade 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 throttle actuator control motor circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. With a DMM, test the throttle actuator control 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

With a DMM, test each throttle actuator control motor 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 17

Go to Step 10

10

With a DMM, test each throttle actuator control 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. With a DMM, test for a short between each throttle actuator control 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 2 throttle actuator control motor circuits at the throttle actuator control 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 throttle actuator control motor 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 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 17

--

15

Inspect for poor connections at the TAC module harness connectors. 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 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 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