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Home >> Cadillac >> 1998 >> Catera >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0120 - TP Sensor Circuit >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  , then go to next step.
  2. Turn ignition on, with engine off. Using scan tool, monitor TP sensor voltage. If TP sensor voltage is 0.3-0.9 volt, go to next step. If TP sensor voltage is not 0.3-0.9 volt, go to step 6).
  3. Fully depress accelerator pedal. If TP sensor voltage is 3.3-3.9 volts, go to next step. If TP sensor voltage is not 3.3-3.9 volts, go to step 6).
  4. Turn ignition on, with engine off. Move/wiggle TP sensor and ECM wiring harness and connectors while observing scan tool display. If TP sensor value on scan tool display changes when moving wiring harness or connectors, go to step 17). If TP sensor value on scan tool display does not change when moving wiring harness or connectors, go to next step.
  5. Turn ignition off. Disconnect TP sensor connector. Using 2 jumper wires, reconnect TP sensor 5 volt reference circuit and ground circuit between wiring harness and TP sensor. Connect DVOM between ground and TP sensor signal circuit terminal at TP sensor. Slowly move throttle plate to Wide Open Throttle (WOT), then return it to closed throttle position while observing voltage display on DVOM. Voltage should increase smoothly to WOT position and decrease smoothly as throttle is slowly closed without any voltage spikes or drop outs noted on DVOM. If TP sensor voltage is as specified, go to step 26). If TP sensor voltage is not as specified, see DIAGNOSTIC AIDS.
  6. Disconnect TP sensor connector. Using DVOM, check voltage between ground and signal circuit at TP sensor harness connector. If voltage 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 disconnected. Disconnect ECM harness connector. Turn ignition on. Using DVOM, check voltage between ground circuit and signal circuit at TP sensor harness connector. If any voltage is present, go to step 21). If no voltage is present, go to next step.
  8. Using DVOM, check harness continuity of TP sensor signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 22).
  9. Using DVOM, check harness continuity between TP sensor signal circuit and ground. If continuity is present, go to step 23). If continuity is not present, go to step 27).
  10. Using DVOM, check voltage between ground and 5 volt reference circuit at TP sensor harness connector. 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 disconnected. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check voltage between ground and 5 volt reference circuit at TP sensor harness connector. If any voltage is present, go to step 18). If no voltage is present, go to next step.
  12. Using DVOM, check harness continuity of TP sensor 5 volt reference circuit. If continuity is present, go to next step. If continuity is not present, go to step 19).
  13. Using DVOM, check harness continuity between TP sensor 5 volt reference circuit and ground. If continuity is present, go to step 20). If continuity is not present, go to step 27).
  14. Turn ignition off. Using a test light connected to battery voltage, probe TP sensor harness connector ground circuit. If test light is illuminates, go to step 16). If test light does not illuminate, go to next step.
  15. Leave TP sensor disconnected. Disconnect ECM harness connector located in engine compartment relay center. Using DVOM, check harness continuity of TP sensor ground circuit. If continuity is present, go to step 27). If continuity is not present, go to step 24).
  16. Turn ignition on, with engine off. Using scan tool, monitor TP sensor voltage. Using a fused jumper wire, jumper signal circuit to ground circuit at TP sensor harness connector. Observe scan tool display. If scan tool displays zero volts, go to step 25). If scan tool does not display zero volts, 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 circuit. After repairs, go to step 29).
  19. Repair open or high resistance in 5 volt reference circuit. 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 or 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 or high resistance in ground circuit. After repairs, go to step 29).
  25. Check for poor connections and terminal tension at TP sensor harness connector. Repair as necessary. After repairs, go to step 29). If connections and terminals are okay, go to next step.
  26. Replace TP sensor. After replacing sensor, go to step 29).
  27. Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 29). If connections and terminals are okay, go to next step.
  28. Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After replacing ECM, go to next step.
  29. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start and operate at greater than 400 RPM. Check for DTCs. If DTC P0120 is set, go to step 2). If DTC P0120 is not set, go to next step.
  30. If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.
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