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Home >> Chevrolet >> 1999 >> Metro Base, 2D Hatchback >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> DTC P0121: Throttle Position (TP) Sensor System Performance (1.8L) >> Diagnosis & Repair

Diagnosis & Repair

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. Connect scan tool to DLC. Turn ignition on, with engine off. Using scan tool, monitor TP sensor angle parameter. Monitor scan tool while depressing accelerator pedal several times. If TP sensor value varies steadily between 10 percent (released position) and 80 percent (depressed position), go to next step. If TP sensor value is not as specified, or reading is erratic, go to step  4 .
  3. Turn ignition on, with engine off. Using scan tool, clear DTC information. Using scan tool, place vehicle into check mode. Operate vehicle within freeze frame conditions. If DTC P0121 resets, go to next step. If DTC P0121 does not reset, go to DIAGNOSTIC AIDS  . Check for an intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
  4. Disconnect TP sensor electrical connector. Using scan tool, monitor TP sensor angle. If TP sensor value is greater than zero percent, go to step  6 . If TP sensor value is zero percent, go to next step.
  5. Connect a test light between TP sensor connector (harness side) reference voltage circuit and TP sensor input circuit. See WIRING DIAGRAMS article. Using scan tool, monitor TP sensor angle. If TP sensor value is greater than 90 percent, go to step  8 . If TP sensor value is 90 percent or less, go to step  7 .
  6. Check for a short to battery voltage in TP sensor input circuit. Check for an open in TP sensor ground circuit between TP sensor and PCM. Check TP sensor electrical connector for proper connection. Repair as necessary. After repairs, go to step  10 . If circuits and connection are okay, go to step  9 .
  7. Check for an open or short in TP sensor input circuit. Check for high resistance in reference voltage circuit between TP sensor and PCM. Repair as necessary. After repairs, go to step  10 . If circuits are okay, go to step  9 .
  8. Replace TP sensor. After repairs, go to step  10 .
  9. Replace PCM. Program PCM using required equipment. After replacing PCM, go to next step.
  10. After repairs, using scan tool, clear DTC information. Road test vehicle within freeze frame conditions that set DTC. Check for DTCs. If no DTCs are stored, repair is complete. If any DTCs are stored, diagnose DTC(s).
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