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 "pre-mature" shut-off of fill nozzle at medium to high flow rates.
^ Nozzle shutting-off after dispensing only 0.2-0.3 gallons (may be less with higher temperatures and/or higher RVP fuels). After a few seconds wait, this process can be repeated.
^ Connect Scan tool and look for DTC's P0446 or P0449.
^ Verify vent path during refueling. Connect Scan tool and go into enhanced [1][2]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 [1][2]EVAP vent solenoid backwards to isolate problem component (vent solenoid, vent pipe/hose, canister, FLVV (fill limit vent valve), etc.