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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Are DTCs P1518 and P1221 both set also? If yes, see DTC P1518: TAC MODULE SERIAL DATA FAULT . If no, go to next step.
  3. Is DTC P1221 set? If yes, see DTC P1221: EXCESSIVE DIFFERENCE BETWEEN THROTTLE POSITION SENSORS . If no, go to next step.
    4. NOTE: The next test must be started within 15 seconds after the ignition is turned ON.
  4. Turn OFF the ignition for 15 seconds. Turn ignition ON, with engine OFF. With a scan tool, observe the TP sensor 1 and TP sensor 2 angle parameters. 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 moved to the released position? If yes, see DIAGNOSTIC AIDS . If no, go to next step.
  5. Turn ignition OFF. Remove the air duct from the throttle body assembly. Disconnect the Throttle Actuator Control (TAC) motor harness connector. Turn ignition ON, with engine OFF. With 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 plate is moved to WOT and decreasing as the throttle plate is moved to the closed position? If yes, go to next step. If no, go to step  13.
  6. Turn ignition OFF. Disconnect the TAC module harness connector containing the TAC motor circuits. Turn ignition ON, with engine OFF. Test the TAC motor circuits for a short to voltage. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  7. Test each TAC motor circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  8. Test each TAC motor circuit for a short to ground. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  9. Disconnect the other TAC module harness connector. Test for a short between each TAC motor circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  10. Turn ignition OFF. Reconnect the TAC module. Connect a test light between the 2 TAC motor circuits at the TAC motor harness connector. Turn ignition ON, with engine OFF and observe the test light. Did the test light illuminate briefly when the ignition was turned ON? If yes, go to next step. If no, go to step  13.
  11. Test for an intermittent and/or poor connections at the TAC motor harness connector. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  12. Replace throttle body assembly. See THROTTLE BODY under AIR INDUCTION SYSTEMS in REMOVAL & INSTALLATION - CORVETTE article. Did you complete the replacement? If yes, go to step  15.
  13. Test for an intermittent and/or poor connections at the TAC module harness connectors. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  14. Replace TAC module. See THROTTLE ACTUATOR CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - CORVETTE article. Did you complete the replacement? If yes, go to next step. Did you complete the replacement? If yes, go to next step.
  15. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  16. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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