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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 260 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0442: EVAP SYSTEM - SMALL 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. Observe the Freeze Frame/Failure Records for this DTC. 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 DIAGNOSTIC AIDS . If no, go to next step.
  3. Inspect the Evaporative Emission (EVAP) system for the following conditions:
    • A loose, missing, or damaged service port dust cap and/or 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 hose.
    • A damaged EVAP vent solenoid or EVAP canister.

    Did you find and correct the condition? If yes, go to step  6. If no, go to next step.

    4. NOTE: 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.
    • Connect the Evaporative Emissions System Tester (EEST) power supply clips to a known good 12-volt source.
    • 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 EVAP Service Port Vent Fitting to open the EVAP service port.
    • Remove the EVAP 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  6. If no, go to next step.

  5. Perform the following:
    • 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 next step. If no, see DIAGNOSTIC AIDS .

  6. 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  3.
  7. 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.