Diagnostic Aids

Symptoms of a blocked inlet path will include:

• An inability to dispense fuel at anything above "trickle" rate, if that. Fuel evident at fill head.
• Nozzle shutting off virtually immediately, since no volume of fuel can be dispensed.

  Suspect a stuck inlet check valve. Check for operation with siphon hose.

  Symptoms of a blocked/restricted vent path include:

  • A "premature" shutoff of fill nozzle at medium to high flow rates.
  • Nozzle shutting off after dispensing only 0.2-0.3 gallons (0.8-1.1 L) (may be less with higher temperatures and/or higher RVP fuels). After a few seconds of waiting, this process can be repeated.

• Connect Scan tool and look for DTCs PO446 or PO449.
• Verify vent path during refueling. Connect Scan tool and go into enhanced EVAP tests to control vent solenoid and read fuel tank pressure sensor.
  • Normal sensor voltage is 1.4 to 1.6 volts. It will decrease with rising tank pressure (during refueling) and during refueling will stabilize just below 1.0 volt.
  • If voltage drops rapidly below this value towards 0.2-0.3 volts during refueling, this is indication that the major vent path is blocked.
  • Check vent path from EVAP vent solenoid backwards to isolate problem component (vent solenoid, vent pipe/hose, canister, FLVV (Fill Limit Vent Valve), etc.)