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Home >> Isuzu >> 1996 >> Hombre S >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Testing >> DTC P0440 - EVAP System >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
    NOTE: Check for other DTCs before proceeding. If any other DTCs are set, diagnose DTCs as necessary.
  2. Turn ignition on, with engine off. Using scan tool, command EVAP canister purge valve and EVAP vent solenoid on and off. If purge valve and vent solenoid click, go to next step. If purge valve and/or vent solenoid do not click, repair wiring or replace purge valve and/or vent solenoid as necessary.
  3. Remove fuel cap. Using scan tool, observe FUEL TANK VACUUM PRESSURE. If pressure is zero in. H2O, go to step 6). If pressure is greater than zero in. H2O, go to next step.
  4. If battery has been disconnected, check fuel tank pressure sensor. See SYSTEM/COMPONENT TESTS article. Replace fuel tank pressure sensor or repair related wiring as necessary. If battery has not been disconnected, go to next step.
  5. Disconnect battery cables. Go to step 3).
  6. Reinstall fuel cap. Using scan tool, command EVAP vent solenoid on (closed). Zero EVAP pressure and vacuum gauges on EVAP Pressure/Purge Cart (J-41413). Connect EVAP pressure/purge cart to EVAP service port. Attempt to pressurize EVAP system to 5 in. H2O. Monitor pressure using gauge on EVAP pressure/purge cart. If pressure can be achieved, go to next step. If pressure cannot be achieved, go to step 8).
  7. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, observe FUEL TANK VACUUM PRESSURE. If pressure reading is 4-6 in H2O, go to step 10). If pressure reading is not 4-6 in. H2O, go to step 9).
  8. Disconnect fuel tank vapor and EVAP purge hoses from EVAP canister. Plug canister fitting for fuel tank vapor hose. Ensure EVAP vent solenoid is still commanded on. Connect a vacuum pump to EVAP purge hose fitting on EVAP canister and apply 5 in. hg. If vacuum holds, go to step 13). If vacuum does not hold, go to step 12).
  9. Check for restricted fuel tank vapor and EVAP purge hoses. Repair as necessary. After repair is completed, go to step 18). If hoses are okay, check fuel tank pressure sensor. See SYSTEM/COMPONENT TESTS article. Replace fuel tank pressure sensor or repair related wiring as necessary.
  10. Disconnect vacuum hose at EVAP canister purge valve (from throttle body). Connect a vacuum pump to EVAP canister purge valve vacuum source fitting. Apply 10 in. Hg. Using scan tool, command EVAP canister purge valve on. If vacuum is released, go to next step. If vacuum holds, go to step 15).
  11. Connect a vacuum gauge to EVAP canister purge valve vacuum hose (from throttle body). Start engine. Raise engine speed to 2000 RPM. If vacuum is greater than 15 in. Hg, see DIAGNOSTIC AIDS. If vacuum is 15 in. Hg or less, go to step 16).
  12. Check for disconnected or damaged vent hose. Also, check for damaged EVAP canister. Repair as necessary. After repair is completed, go to step 18). If no problem is found, go to step 17).
  13. Check for missing or faulty fuel cap. Check for disconnected or leaking fuel tank vapor hose or disconnected or damaged EVAP purge hose. Repair as necessary. After repair is completed, go to step 18). If no problem is found, go to next step.
  14. Using scan tool, command EVAP vent solenoid on. With EVAP pressure/purge cart connected to EVAP service port, attempt to pressurize EVAP system by leaving cart control knob in PRESSURIZE position. Using Ultrasonic Leak Detector (J-41416) , locate and repair EVAP system leak. It may be necessary to partially lower fuel tank to examine hose connections at top of tank. After repair is completed, go to step 18).
  15. Replace EVAP canister purge valve. After repair is completed, go to step 18).
  16. Locate and repair cause of low or no vacuum. After repair is completed, go to step 18).
  17. Replace EVAP vent solenoid. After repair is completed, go to next step.
  18. Turn ignition on, with engine off. Using scan tool, command EVAP vent solenoid on (closed). Using EVAP pressure/purge cart, pressurize EVAP system to 15 in. H2O. Set rotary switch on pressure/purge cart to HOLD, and observe EVAP pressure gauge. If pressure decreases to 10 in. H2O within 2 minutes, system is functioning properly. If pressure does not decrease to 10 in. H2O within 2 minutes, repeat step 2).
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