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Home >> Pontiac >> 2000 >> Firebird Formula, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 5.7L >> Diagnostic Tests >> DTC P1518: Throttle Actuator Control (TAC) Module Serial Data Circuit ("Y" Body) >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Turn ignition on, engine off. Using test light connected to ground, probe both ends of THROT CONT fuse (located in underhood fuse block). If test light illuminates on at least one side of fuse, go to next step. If test light does not illuminate on either end of fuse, check ignition relay.
  3. Turn ignition off. Using test light probe both ends of THROT CONT fuse. If test light illuminates, go to step  31. If test light does not illuminate, go to next step.
  4. Using scan tool, verify if DTC P0606 is also set. If DTC P0606 is set, diagnose DTC P0606 first. See DTC P0606: PCM INTERNAL PERFORMANCE ("Y" BODY) . If DTC P0606 is not set, go to next step.
    NOTE: If Driver Information Center (DIC) is displaying REDUCED ENGINE POWER, go to step  6.
  5. Operate engine at idle then increase engine speed to 3000 RPM, if possible. Using scan tool, monitor DTC option. If this DTC fails this ignition cycle, go to next step. If this DTC does not fail this ignition cycle, see DIAGNOSTIC AIDS .
  6. Turn ignition off. Disconnect throttle actuator harness connector. Turn ignition on, with engine off. Check voltage at both circuits of throttle actuator motor harness connector. If both circuits read greater than 8 volts, go to step  12. If both circuits do not read greater than 8 volts, go to next step.
  7. Turn ignition off. Check resistance on both throttle actuator motor harness connector circuits. If resistance is 0-5 ohms, go to step  10. If resistance is not 0-5 ohms, go to next step.
  8. Turn ignition off. Remove THROT CONT fuse. Check continuity from TAC side of fuse terminal to battery ground. If continuity exists, go to next step. If continuity does not exist, go to step  11.
  9. Disconnect TAC module harness connector. Check continuity from TAC side of fuse terminal to battery ground. If continuity exists, go to step  22. If continuity does not exist, go to step  32.
  10. Disconnect TAC module harness connector. Check continuity from throttle actuator motor harness connector to battery ground. If continuity exists, go to step  23. If continuity does not exist, go to step  32.
  11. Turn ignition off. Disconnect TAC harness connector. Check continuity between TAC side of fuse terminal to ignition feed circuit of TAC at harness connector. If continuity exists, go to step  32. If continuity does not exist, go to step  24.
  12. Turn ignition off. Disconnect TAC module harness connector. Turn ignition on, with engine off. Check voltage at both circuits of throttle actuator motor harness connector. If both circuits read zero volts, go to next step. If both circuits do not read zero volts, go to step  25.
  13. Turn ignition off. Disconnect TAC module harness connector. Check continuity of both throttle actuator motor circuit to all other TAC module terminals. If continuity exists, go to step  30. If continuity does not exist, go to next step.
  14. Check continuity from TAC module ground circuit to battery ground. If continuity exists, go to next step. If continuity does not exist, go to step  26.
  15. Check voltage at serial data circuits in TAC module harness connector. If both serial data circuits read 0-4.5 volts, go to next step. If both serial data circuits do not read 0-4.5 volts, go to step  18.
  16. Turn ignition off. Check resistance from serial data circuits at TAC module harness connector to battery ground. If DVOM reads OL for both circuits, go to step  20. If DVOM does not read OL for both circuits, go to next step.
  17. Disconnect PCM harness connector. Check resistance from serial data circuits at TAC module harness connector to battery ground. If resistance is 0-5 ohms, go to step  27. If resistance is not 0-5 ohms, go to next step.
  18. Disconnect PCM harness connector. Check continuity of each serial data circuit between TAC module harness connector to PCM harness connector. If continuity is exists on either circuit, go to step  30. If continuity does not exist on either circuit, go to next step.
  19. Check voltage on both serial data circuits at TAC module harness connector. If voltage is indicated on either circuit, go to step  28. If voltage is not indicated on either circuit, go to step  33.
  20. Disconnect PCM harness connector. Check continuity of each serial data circuit between TAC module harness connector and PCM harness connector. If continuity is indicated on both circuits, go to next step. If continuity is not indicated on both circuit, go to step  29.
  21. Reconnect PCM. Turn ignition on, with engine off. Check voltage at serial data circuit at TAC module harness connector. If voltage reading is zero volts, go to step  33. If voltage reading is not zero volts, go to step  32.
  22. Repair TAC module ignition feed circuit for short to ground. After repairs, go to step  34.
  23. Repair throttle actuator motor circuit for short to ground. After repairs, go to step  34.
  24. Repair TAC module ignition feed circuit for an open in circuit. After repairs, go to step  34.
  25. Repair throttle actuator motor circuits for short to voltage. After repairs, go to step  34.
  26. Repair TAC module ground for open. After repairs, go to step  34.
  27. Repair serial data circuit for short to ground. After repairs, go to step  34.
  28. Repair serial data circuit for short to voltage. After repairs, go to step  34.
  29. Repair serial data circuit for an open in affected circuit. After repairs, go to step  34.
  30. Repair circuits that shows continuity. After repairs, go to step  34.
  31. Repair ignition feed circuit for short to voltage. After repairs, go to step  34.
  32. Replace TAC module. After replacing module, go to step  34.
  33. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  34. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within conditions that set DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step  2.
  35. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.
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