Mike's Workshop Manuals: Service manuals for every vehicle
Home >> Chevrolet >> 1999 >> Forward Control P12 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes - DTC P0704-P1272 >> DTC P1221 >> DTC P1221: TP Sensor Circuit (3.0L "V" Body) >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
  2. Turn ignition on, with engine off. Using scan tool, monitor TP sensor voltage. If scan tool voltage reading is 0.3-0.9 volt, go to next step. If scan tool voltage reading is not 0.3-0.9 volt, go to step  6.
  3. Fully depress accelerator pedal. If scan tool voltage reading is 4-5 volts, go to next step. If scan tool voltage reading is not 4-5 volts, go to step  6.
  4. Wiggle/move TP sensor and ECM harness connectors while observing scan tool display. If TP sensor value is affected by moving harness or connectors, go to step  17. If TP sensor value is not affected by moving harness or connectors, go to next step.
  5. Turn ignition off. Disconnect TP sensor harness connector. Using 2 jumper wires, jumper TP sensor 5-volt reference and ground circuit between harness connector and sensor. Connect DVOM to 5-volt reference circuit between sensor and harness connector. Turn ignition on, with engine off. Slowly move throttle to Wide Open Throttle (WOT), then slowly return to closed position while observing voltage on DVOM. Voltage should increase and decrease smoothly as throttle is moved to WOT and closed throttle position. If voltage changes smoothly, see DIAGNOSTIC AIDS . If voltage does not change smoothly (spikes or drops out), go to step  26.
  6. Disconnect TP sensor harness connector. Using DVOM, check voltage between battery ground and TP sensor signal circuit at harness connector. If voltage reading is 4.7-5.3 volts, go to step  10. If voltage is not 4.7-5.3 volts, go to next step.
  7. Turn ignition off. Leave TP sensor harness connector disconnected. Disconnect ECM harness connector. Turn ignition on. Using DVOM, check voltage between battery ground and TP sensor signal circuit at harness connector. If any voltage is present, go to step  21. If no voltage is present, go to next step.
  8. Check for continuity in TP sensor signal circuit. If continuity exists, go to next step. If continuity does not exist, go to step  22.
  9. Check for continuity between TP sensor signal circuit and battery ground. If continuity exists, go to step  23. If continuity does not exist, go to step  27.
  10. If voltage is 4.7-5.3 volts, go to step  14. If voltage is not 4.7-5.3 volts, go to next step.
  11. Turn ignition off. Leave TP sensor harness connector disconnected. Disconnect ECM harness connector. Turn ignition on, with engine off. If any voltage is present, go to step  18. If voltage is not present, go to next step.
  12. Check continuity on TP sensor 5-volt reference circuit. If continuity exists, go to next step. If continuity does not exist, go to step  19.
  13. Check continuity between TP sensor 5-volt reference circuit and battery ground. If continuity exists, go to step  20. If continuity does not exist, go to step  27.
  14. Turn ignition off. Using test light connected to battery voltage, probe TP sensor ground circuit at harness connector. If test light illuminates, go to step  16. If test light does not illuminate, go to next step.
  15. Leave TP sensor harness connector. Disconnect ECM harness connector. Check continuity of TP sensor ground circuit at harness connector. If continuity exists, go to step  27. If continuity does not exist, go to step  24.
  16. Turn ignition on, with engine off. Using a fused jumper wire, jumper TP sensor signal circuit to TP sensor ground circuit. Using scan tool, monitor TP sensor voltage. If scan tool voltage reading is 0.5 volt, go to step  25. If scan tool voltage reading is not 0.5 volt, go to step  28.
  17. Repair harness or connections as necessary. After repairs, go to step  29.
  18. Repair short to voltage in 5-volt reference. After repairs, go to step  29.
  19. Repair open/high resistance in 5-volt reference. After repairs, go to step  29.
  20. Repair short to ground in 5-volt reference circuit. After repairs, go to step  29.
  21. Repair short to voltage in signal circuit. After repairs, go to step  29.
  22. Repair open/high resistance in signal circuit. After repairs, go to step  29.
  23. Repair short to ground in signal circuit. After repairs, go to step  29.
  24. Repair open/high resistance in ground circuit. After repairs, go to step  29.
  25. Check for poor connection or poor terminal tension. If problem is found, go to step  29. If no problem is found, go to next step.
  26. Replace TP sensor. After replacing sensor, go to step  29.
  27. Check for poor connection or poor terminal tension at ECM harness connection. If problem is found, go to step  29. If no problem is found, go to next step.
  28. Replace ECM. Program replacement ECM using required equipment and program ECM with frequency code of theft deterrent module that is currently on vehicle. After replacing ECM, go to next step.
  29. 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 this 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.
  30. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.
scientia non olet · About Mike's Workshop Manuals