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Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Isuzu Trooper. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform ON-BOARD DIAGNOSTIC II SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD-II system check, go to next step.
  2. If any other DTCs other than P0172 or P0175 are set, diagnose affected DTCs before proceeding. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
  3. Using scan tool, observe BANK 2 L.T. FUEL TRIM values. While operating vehicle within CODE ENABLE CRITERIA  conditions. If L.T. FUEL TRIM value is less than -15 percent (automatic transmission) or -12 percent (manual transmission), go to step  5. If value is more than specified, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within CODE ENABLE CRITERIA  conditions. On scan tool, monitor DTC information. If scan tool indicates DTC P0175 FAILED THIS IGNITION, go to next step. If scan tool display is not as specified, and a rich condition is not present but driveability problem exists, repair by symptom. See TROUBLE SHOOTING - NO CODES article.
  5. If DTC P0172 is also set, go to next step. If DTC P0172 is not set, go to step  15.
  6. Check air filter element condition. Replace air filter element if necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If air filter element is okay, go to next step.
  7. Check for collapsed or restricted air intake duct. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  8. Check MAF inlet screen for damage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  9. Start engine. If a low or unsteady idle condition is present, go to next step. If idle is okay, go to step  11.
  10. Turn ignition off. Check throttle body bore and throttle plate for coking or foreign objects. Check for clogged Idle Air Control (IAC) passages. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  11. Disconnect vacuum hose from fuel pressure regulator and check hose for presence of fuel. If fuel is present, replace fuel pressure regulator. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no fuel is present, go to next step.
  12. Turn ignition on. Use scan tool to read TP1 ANGLE while slowly depressing accelerator pedal. TP1 ANGLE should increases steadily from a minimum of 8 percent at closed throttle to a maximum of 92 percent at wide open throttle. If TP1 ANGLE displays as specified, go to next step. If TP1 ANGLE does not display as specified, go to step  21.
  13. Disconnect MAF sensor 3-pin harness connector. On scan tool, observe BANK 2 L.T. and BANK 2 S.T. FUEL TRIM values, while operating vehicle within CODE ENABLE CRITERIA . BANK 2 L.T. and BANK 2 S.T. FUEL TRIM values should both display about zero percent. If both FUEL TRIM values display as specified, go to step  22. If both FUEL TRIM values do not display as specified, go to next step.
  14. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If problem with fuel system is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  15. Turn ignition off. Disconnect EVAP canister purge valve 2-pin harness connector. EVAP canister purge valve is located at front of intake manifold under throttle body. Connect test light between EVAP canister purge valve harness connector terminals No. 1 (Red/Blue wire) and No. 2 (Black/Yellow wire). Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step  19.
  16. Using a DVOM, check for short to ground on in Red/Blue wire between EVAP canister purge valve harness connector terminal No. 1 and PCM harness connector E-22 terminal No. 7. See WIRING DIAGRAMS article. If problem is found, go to next step. If no problem is found, go to step  18.
  17. Repair short to ground in Red/Blue wire. After repair, use scan tool to verify repair.
  18. Replace and reprogram PCM. See POWERTRAIN CONTROL MODULE REPLACEMENT  under POWERTRAIN CONTROL MODULE. Use scan tool to clear DTC and verify repair.
  19. Perform FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM & COMPONENT TESTING article. If problem with fuel injectors is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  20. Remove Bank 2 HO2S No. 1 and check for silicone contamination (powdery white deposit). If HO2S is contaminated, replace Bank 2 HO2S No. 1. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If Bank 2 HO2S No. 1 is not contaminated, check for an intermittent problem. See DIAGNOSTIC AIDS .
  21. Check for loose TPS sensor mounting screws. Tighten or replace missing screws as necessary. If mounting screws are tight, replace TPS. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
  22. Replace MAF sensor. See ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION article. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
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