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Home >> Pontiac >> 2001 >> Firebird Formula, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 5.7L >> Diagnostic Tests >> DTC P0121: Throttle Position Sensor Circuit Insufficient Activity >> Diagnostic Procedures

Diagnostic Procedures

  1. If powertrain diagnostic system check was performed, go to next step. If powertrain diagnostic system check was not performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under DIAGNOSTIC SYSTEM TESTS. After performing powertrain diagnostic system check, go to next step.
  2. Start and idle engine. Using scan tool, check for additional DTCs. If DTC P0107, P0180, P1404, P1635 or P1639 are also set, diagnose those DTCs first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If these DTCs are not set, go to next step.
  3. Start engine. Monitor MAP sensor voltage on scan tool. Increase engine speed to 2000 RPM. If MAP sensor voltage changed when engine speed changed, go to step  8. If MAP sensor voltage did not change when engine speed changed, go to next step.
  4. Turn engine on. Locate MAP sensor and PCM. See Figure and Figure . Move/wiggle MAP sensor and PCM connectors. If MAP value changes when harness or connectors are moved, go to step  16. If MAP value does not change, go to next step.
  5. Turn ignition off. Remove MAP sensor from intake manifold. Leave harness connector connected. Install a hand-held vacuum pump to MAP sensor. Turn ignition on and monitor MAP sensor value on scan tool. Note MAP sensor value with no vacuum applied. Slowly apply vacuum one in. Hg at a time to MAP sensor (up to 20 in. Hg). Each inch of vacuum applied should result in a 3-4 kPa drop in MAP sensor value on scan tool. If MAP sensor value changes smoothly, go to next step. If MAP sensor value does not change or is erratic, go to step  17.
  6. Apply 20 in. Hg to MAP sensor using hand-held vacuum pump. If MAP reading is 34 kPa or less, go to next step. If MAP reading is not 34 kPa or less, go to step  17.
  7. Disconnect vacuum source from MAP sensor. If MAP reading returns to original value measured in step  5, go to next step. If MAP reading does not return to original value, go to step  17.
  8. Turn ignition on. Using scan tool, monitor TP sensor voltage while moving accelerator from closed to wide open throttle. TP sensor reading should change from less than one volt to more than 4 volts. If TP sensor reading is as specified, go to next step. If TP sensor reading is not as specified, go to step  10.
  9. Review and record FREEZE FRAME and/or FAILURE RECORDS data for this DTC. Turn ignition off for at least 30 seconds. Reinstall MAP sensor and reconnect any disconnected components. Start engine. Operate vehicle within conditions required for diagnostic run, and as close to conditions recorded in FREEZE FRAME and/or FAILURE RECORDS as possible. Using scan tool, select DTC option, SPECIFIC DTC option, and then enter this DTC which was set. If scan tool indicates that this diagnostic failed this ignition cycle, go to next step. If scan tool does not indicate that this diagnostic failed in this ignition cycle, see DIAGNOSTIC AIDS .
  10. Turn ignition off. Locate and disconnect TP sensor harness connector. See Figure. Turn ignition on. Monitor TP sensor display on scan tool. If TP voltage is zero volts, go to next step. If TP sensor is not zero volts, go to step  13.
  11. Monitor TP sensor display on scan tool. Connect a fused jumper wire between TP sensor connector terminals "A" (Gray wire) and "C" (Dark Blue wire). If TP sensor voltage is about 5 volts, go to next step. If TP sensor voltage is not about 5 volts, go to step  14.
  12. Replace TP sensor. See REMOVAL, OVERHAUL & INSTALLATION - CARS article. After replacing sensor, go to step  18.
  13. Check for short to voltage in Dark Blue wire between TP sensor connector terminal "C" and PCM connector C2 terminal No. 24. See Figure. Check for high resistance or poor connections in Black wire between TP sensor connector terminal "B" and PCM connector C1 terminal No. 60. Repair as necessary. After repairs, go to step  18. If circuits are okay, go to step  15.
  14. Check for poor connection or high resistance in Gray wire between TP sensor connector terminal "A" and PCM connector C1 terminal No. 8. See Figure. Repair as necessary. After repairs, go to step  18. If circuits are okay, go to next step.
  15. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - CARS article. After replacing PCM, go to step  18.
  16. Locate and repair suspect circuits. After repairs, go to step  18.
  17. Replace MAP sensor. See REMOVAL, OVERHAUL & INSTALLATION - CARS article. After replacing sensor, go to next step.
  18. Using scan tool, clear DTCs. Turn ignition off for at least 30 seconds. Start engine and allow it to reach normal operating temperature. Operate vehicle within conditions for setting 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, go to step  2.
  19. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no undiagnosed DTCs are displayed, system is okay.
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