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Home >> Chevrolet >> 2002 >> Camaro Base, 2D Convertible, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P1120: Throttle Position Sensor 1 Circuit >> Diagnostic Procedures

Diagnostic Procedures

  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. NOTE: If the code does not set this ignition, see DIAGNOSTIC AIDS .
  2. Turn ON the ignition, with the engine OFF. With a scan tool, observe the Agree/Disagree parameter of the TP sensors 1 and 2. Does the scan tool indicate Disagree? If yes, go to next step. If no, go to step  11.
  3. With a scan tool, observe the TP sensor voltage parameter. Depress the throttle to Wide Open Throttle (WOT) and release. Does the scan tool indicate voltage at or near 1 V throughout throttle travel? If yes, go to step  21. If no, go to next step.
  4. Does scan tool indicate voltage below 1 V throughout throttle travel? If yes, go to next step. If no, go to step  7.
  5. With a scan tool, observe the TP sensor voltage parameter. Disconnect the TAC throttle body. Does the scan tool indicate voltage at or near 5 V when the TAC is disconnected? If yes, go to next step. If no, go to step  13.
  6. Turn OFF the ignition for 15 seconds. Turn ON the ignition, with the engine OFF. Measure the voltage on the 5-volt reference circuit using a DMM that is connected to a good ground. Does the voltage measure 3.9-4.6 V? If yes, go to step  23. If no, go to step  17.
  7. Disconnect the TAC throttle body. Turn ON the ignition, with the engine OFF. With a scan tool, observe the TP sensor voltage parameter. Connect a test lamp between the signal and low reference circuits. Does the scan tool indicate voltage at 0 V when the test lamp is installed? If yes, go to step  10. If no, go to next step.
  8. Remove the test lamp from the low reference circuit. Connect the test lamp to a good ground. Does the scan tool indicate voltage at 0 V when the test lamp is installed? If yes, go to step  14. If no, go to next step.
  9. Did the test lamp illuminate when connected between the signal circuit and ground? If yes, go to step  15. If no, go to step  16.
  10. Turn OFF the ignition for 15 seconds. Turn ON the ignition, with the engine OFF. Measure the voltage on the 5-volt reference circuit using a DMM that is connected to a good ground. Does the voltage measure 3.9-4.6 V? If yes, go to step  23. If no, go to step  18.
  11. Inspect the following fuses:
    • ELEC.
    • THROT.
    • CONT.
    • TCS.
    • BATT.

    Are the fuses okay? If yes, go to next step. If no, go to step  19.

  12. Disconnect the TAC module. Probe the feed circuits using a test lamp with a test lamp that is connected to a good ground. Does the test lamp illuminate when probing the feed circuits? If yes, see DTC P1515: COMMANDED & ACTUAL THROTTLE POSITION MISMATCH  or DTC P1516: COMMANDED & ACTUAL THROTTLE POSITION MALFUNCTION  . If no, go to step  20.
  13. Test the signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step  27. If no, go to step  26.
  14. Test the low reference circuit for an open. Did you find and correct the condition? If yes, go to step  27. If no, go to step  25.
  15. Test the signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  27. If no, go to step  26.
  16. Test the signal circuit for an open. Did you find and correct the condition? If yes, go to step  27. If no, go to step  25.
  17. Test the 5-volt reference circuit for an open or short to ground. Did you find and correct the condition? If yes, go to step  27. If no, go to step  25.
  18. Test the 5-volt reference circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  27. If no, go to step  26.
  19. Repair the short to ground in the feed circuit. After repairs, go to step  27.
  20. Repair the open in the feed circuit. After repairs, go to step  27.
  21. Test the low reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step  27. If no, go to next step.
  22. Test for continuity between the 5-volt reference circuit in the TAC and ground. Is continuity indicated? If yes, go to step  24. If no, go to step  26.
  23. Inspect for a poor connection at the TAC. Did you find and correct the condition? If yes, go to step  27. If no, go to next step.
  24. Replace the throttle body of the TAC assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  27.
  25. Inspect for a poor connection at the TAC module. Did you find and correct the condition? If yes, go to step  27. If no, go to next step.
  26. Replace the TAC module. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to next step.
  27. 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.
  28. 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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