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HOMESERVICE MANUALSCHEVROLET1995CAVALIER LS, 4D SEDAN, 2.2 4REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODES - 2.3L (W/OBD-II)DIAGNOSTIC TROUBLE CODESDTC P0171- FUEL TRIM SYSTEM LEANDIAGNOSTIC PROCEDURES
1995 Chevrolet Cavalier LS, 4D Sedan, 2.2 4

Diagnostic Procedures

1995 Chevrolet Cavalier LS, 4D Sedan, 2.2 4SECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
  3. Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select FUEL TRIM INDEX. If fuel trim index is less than 160, go to next step. If fuel trim index is greater than specification, go to step 5).
  4. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If fuel trim index is less than 160, go to DIAGNOSTIC AIDS. If fuel trim index is greater than specification, go to next step.
  5. Check vacuum hoses for splits, kinks and proper routing. Check PCV valve for proper installation. Check for fuel contamination. Check PCM and sensor grounds. Check O2S 1 for correct installation and ensure O2S 1 wiring is not in contact with exhaust manifold. If no problems are found, go to next step. If any problem is found, go to step 7).
  6. Disconnect MAP sensor connector. Operate vehicle in closed loop while monitoring FUEL INDEX TRIM. If fuel trim index is less than 160, go to step 16). If fuel trim index is greater than specification, go to step 9).
  7. Repair fault that was detected in step 5). Operate vehicle in closed loop while monitoring FUEL INDEX TRIM. If fuel trim index is less than 160, go to next step. If fuel trim index is greater than 160, go to step 9).
  8. Lean condition is not present at this time. If a driveability problem exists, go to TESTS W/O CODES article. If no driveability problem exist, perform OBD System Check.
  9. Check vacuum hoses for splits, kinks and proper routing. Check throttle body, intake manifold and injector "O" rings for vacuum leaks. Repair as necessary. After repair is completed, perform OBD System Check. If no repairs are necessary, go to next step.
  10. Start engine and allow it to idle. Using scan tool, check IAC count. If IAC count is more than 5, go to next step. If IAC count is 5 or less, go to step 12).
  11. Check for fuel contamination. Repair as necessary. After repair is completed, perform OBD System Check. If fuel is okay, go to step 13).
  12. Go to DTC P0506 or P0507 to check IAC valve performance. Repair as necessary. After repair is completed, perform OBD System Check. If IAC valve is okay, go to next step.
  13. Connect a fuel pressure gauge to fuel system. Cycle ignition switch 2-3 times. With fuel pump running, observe fuel pressure. If fuel pressure is 41-47 psi (284-325 kPa), go to next step. If fuel pressure is not 41-47 psi (284-325 kPa), repair fuel system as necessary. See appropriate SYSTEM/COMPONENT TESTS article.
  14. Ensure engine is at normal operating temperature. Start engine and allow it to idle. Observe fuel pressure. Fuel pressure noted in step 13) should drop 3-10 psi (21-69 kPa). If fuel pressure is as specified, perform injector balance test. See FUEL SYSTEM in appropriate SYSTEM/COMPONENT TESTS article. If fuel pressure is not as specified, see CHART A-7  .
  15. Remove crankcase oil/air separator for easy access to fuel injectors. See CHART C-2A in SYSTEM/COMPONENT TESTS article. Replace any injector found faulty as necessary and after each repair perform OBD System Check. If not a single injector was found faulty, see DIAGNOSTIC AIDS.
  16. Replace MAP sensor. After repair is completed, go to next step.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.