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.)