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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 81 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P1221: Excessive Difference Between Throttle Position Sensors >> Diagnostic Procedures

Diagnostic Procedures

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  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. Is DTC P1518 also set? If yes, see DTC P1518: TAC MODULE SERIAL DATA FAULT . If no, go to next step.
  3. Turn ON the ignition, with the engine OFF. With a scan tool, observe the TP sensor 1 and 2 Agree/Disagree parameter. Does the scan tool TP sensor 1 and 2 Agree/Disagree parameter indicate Disagree? If yes, go to step  5. If no, go to next step.
  4. Remove the air inlet duct from the throttle body. Disconnect the throttle actuator motor harness connector. Slowly open the throttle blade to Wide Open Throttle (WOT) and back to the closed throttle position several times by hand while observing the scan tool TP sensor Agree/Disagree parameter. Does the TP sensor Agree/Disagree parameter change from Agree to Disagree during the above test? If yes, go to step  18. If no, go to next step.
  5. Disconnect the TP sensor harness connector. Disconnect the TAC module harness connectors Test the TP sensor 1, 5-volt reference circuit for resistance. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  6. With a Digital Multimeter (DMM), test for a short between the TP sensor 1, 5-volt reference circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  7. With a DMM, test the TP sensor 1 signal circuit for resistance. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  8. With a DMM, test for a short between the TP sensor 1 signal circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  9. With a DMM, test the TP sensor 1 low reference circuit for resistance. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  10. With a DMM, test for a short between the TP sensor 1 low reference circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  11. With a DMM, test the TP sensor 2, 5-volt reference circuit for resistance. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  12. With a DMM, test for a short between the TP sensor 2, 5-volt reference circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  13. With a DMM, test the TP sensor 2 signal circuit for resistance. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  14. With a DMM, test for a short between the TP sensor 2 signal circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  15. With a DMM, test the TP sensor 2 low reference circuit for resistance. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  16. With a DMM, test for a short between the TP sensor 2 low reference circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  17. Inspect for poor connections at the harness connector of the TAC module. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  18. Inspect for poor connections at the harness connector of the TP sensor. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
    19. NOTE: The throttle body and the throttle position sensor assembly should be replaced as a unit. Driveability concerns may result if either is replaced individually.
  19. Replace the throttle body assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to next step.
  20. 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.
  21. 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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