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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 260 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0440: EVAP SYSTEM - LARGE LEAKDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Inspect the Evaporative Emission (EVAP) system for the following conditions:
    • A loose, missing, or damaged service port Schrader valve.
    • A loose, incorrect, missing, or damaged fuel fill cap.
    • A damaged EVAP canister purge solenoid.

    Raise and support vehicle. Inspect the EVAP system for the following conditions:

    • Any disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses.
    • A damaged EVAP vent solenoid or EVAP canister.

    Did you find and correct the condition? If yes, go to step  17. If no, go to next step.

    3. NOTE: Larger volume fuel tanks and/or those with lower fuel levels may require several minutes for the floating indicator to stabilize.
  3. Perform the following:
    • Turn ignition off.
    • Connect the Evaporative Emissions System Tester (EEST) power supply clips to a known good 12-volt source.
    • Turn the nitrogen/smoke valve to nitrogen.
    • Connect the nitrogen/smoke hose to the 0.20 in. (0.5 mm) test orifice on the bottom-front of the EEST.
    • Use the remote switch to activate the EEST.
    • Align the red flag on the flow meter with the floating indicator. Use the remote switch to de-activate the EEST.
    • Install the Fuel Tank Cap Adapter to the fuel fill pipe.
    • Install the fuel fill cap to the Fuel Tank Cap Adapter.
    • Remove the nitrogen/smoke hose from the test orifice and install the hose onto the Fuel Tank Cap Adapter.
    • Turn ignition on, with engine off.
    • Command the EVAP canister vent solenoid valve closed with a scan tool.
    • Use the remote switch to introduce nitrogen and fill the EVAP system until the floating indicator stabilizes.
    • Compare the flow meter's stable floating indicator position to the red flag.

    Is the floating indicator below the red flag? If yes, go to step  6. If no, go to next step.

    4. NOTE: Important Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. System flow will be less with higher temperatures.
  4. Perform the following:
    • Turn ignition off.
    • Install the Fuel Tank Cap Adapter to the fuel fill pipe.
    • Connect the fuel fill cap to the Fuel Tank Cap Adapter.
    • Connect the EEST nitrogen/smoke supply hose to the Fuel Tank Cap Adapter.
    • Turn ignition on, with engine off.
    • Command the EVAP vent solenoid closed with a scan tool.
    • Turn the nitrogen/smoke valve on the EEST control panel to SMOKE.
    • Use the remote switch to introduce smoke into the EVAP system.
    • Use the Service Port Vent Fitting to open the EVAP service port.
    • Remove the Service Port Vent Fitting once smoke is observed.
    • Continue to introduce smoke into the EVAP system for an additional 60 seconds.
    • Inspect the entire EVAP system for exiting smoke with the High Intensity White Light.
    • Continue to introduce smoke at 15 second intervals until the leak source has been located.

    Did you locate and repair a leak source? If yes, go to step  21. If no, go to next step.

  5. Disconnect the Fuel Tank Cap Adapter from the fuel fill pipe. Install the fuel fill cap to the fuel fill pipe. Connect the EEST nitrogen/smoke supply hose to the EVAP service port. Use the remote switch to introduce smoke into the EVAP system. Inspect the entire EVAP system for exiting smoke with the High Intensity White Light. Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to step  21. If no, go to next step.
  6. Use the remote switch to stop introducing smoke. Install the Fuel Tank Cap Adaptor to the fuel fill pipe. Connect the EEST nitrogen/smoke supply hose to the Fuel Tank Cap Adaptor. Connect the vehicle fuel fill cap to the Fuel Tank Cap Adaptor. Command the EVAP vent solenoid open with a scan tool. Compare the FUEL TANK PRESSURE SENSOR parameter with a scan tool, to the EEST pressure/vacuum gage. Is the scan tool FUEL TANK PRESSURE SENSOR parameter within 1 in. H2O of the EEST pressure/vacuum gage? If yes, go to next step. If no, go to step  18.
  7. Seal the EVAP system using the EVAP PURGE/SEAL function with a scan tool. Turn the nitrogen/smoke valve on the EEST control panel to NITROGEN. Use the EEST to pressurize the EVAP system to 10 in. H2O. Is the FUEL TANK PRESSURE SENSOR parameter more than 5 in H2O? If yes, go to next step. If no, go to step  14.
  8. Use the remote switch to stop introducing nitrogen into the EVAP system. Increase the EVAP canister purge solenoid to 100 percent. Is the FUEL TANK PRESSURE SENSOR parameter less than 1 in H2O? If yes, go to next step. If no, go to step  11.
  9. Perform the following:
    • Connect the nitrogen/smoke hose to the EVAP service port.
    • Remove the Fuel Tank Cap Adaptor.
    • Install the fuel fill cap to the fuel fill pipe.
    • Start the engine.
    • Allow the engine to idle.
    • Use the PURGE/SEAL function to seal the system with a scan tool.
    • Command the EVAP canister purge solenoid to 30 percent.
    • Observe the vacuum/pressure gage on the EEST and the FUEL TANK PRESSURE SENSOR parameter on the scan tool.
    • Allow the vacuum to increase on the gage of the EEST, until it reaches approximately 16 in. H2O.
    • Use the PURGE/SEAL function to seal the system with a scan tool.

    Is the FUEL TANK PRESSURE SENSOR parameter on the scan tool within 1 in H2O of the vacuum/pressure gage on the EEST, until the vacuum reached the abort limit on a scan tool. If yes, go to next step. If no, go to step  14.

  10. Did the FUEL TANK PRESSURE SENSOR parameter on a scan tool display more than 3.2 volts? If yes, see DIAGNOSTIC AIDS . If no, go to step  14.
  11. Disconnect the EVAP purge pipe from the EVAP canister purge solenoid. Is the FUEL TANK PRESSURE SENSOR parameter less than 1 in. H2O? If yes, go to step  19. If no, go to next step.
  12. Disconnect the EVAP purge pipe at the EVAP canister. Is the FUEL TANK PRESSURE SENSOR parameter less than 1 in. H2O? If yes, go to step  17. If no, go to next step.
  13. Disconnect the EVAP vapor pipe at the EVAP canister. Is the FUEL TANK PRESSURE SENSOR parameter less than 1 in. H2O? If yes, go to step  20. If no, go to step  16.
  14. Test for an intermittent and/or poor connections at the Fuel Tank Pressure (FTP) sensor. Did you find and correct the condition? If yes, go to step  21. If no, go to next step.
  15. Test the FTP sensor low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.
  16. Repair the pinched or obstructed EVAP vapor pipe. Did you complete the repair? If yes, go to step  21.
  17. Repair the restriction in the EVAP purge pipe. See EVAP HOSES/PIPES - ENGINE/CHASSIS under EMISSION SYSTEMS & SUB-SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the repair? If yes, go to step  21.
  18. Replace the FTP sensor. See FUEL TANK PRESSURE SENSOR under SENSORS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  21.
  19. Replace the EVAP canister purge solenoid. See EVAP CANISTER PURGE SOLENOID under MOTORS & SOLENOIDS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  21.
  20. Replace the EVAP canister. See EVAP CANISTER under EMISSION SYSTEMS & SUB-SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to next step.
  21. Perform the Service Bay Test. See SERVICE BAY TEST  under DRIVE CYCLES. Does the scan tool indicate that the Service Bay Test passed? If yes, go to next step. If no, go to step  2.
  22. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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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.