Diagnostic Test

THEORY OF OPERATION 

During a re-fueling event, as fuel enters the Fuel Tank, the fuel vapors in the tank must be vented to prevent early fuel shut off. On a properly functioning system the vapors escape the tank through the Liquid / Vapor Separator and Drain Valve (LVS), through a tube connected to the Fuel Tank Isolation Valve (FTIV). The normally closed FTIV opens when the Refuel button is pressed. The Refuel button is hard wired to BCM. The BCM sends a bus message to the PCM to open the FTIV to relieve the pressure in the Fuel Tank. The vapors pass through the FTIV and flow to the Charcoal Canister. The fuel vapors are trapped by the charcoal in the canister. The clean air passes through a tube to the Electronic Leak Check Module (ELCM) and vents through the Fresh Air Filter, and out to the atmosphere. When the fuel level in the tank rises and the liquid fuel reaches the LVS, the float closes the vapor venting orifice inside the valve. The pressure inside the tank will increase causing the Inlet Check Valve (ICV) to close and fuel to back up inside the filler tube. When the fuel reaches the sensing port aspirator in the fuel fill nozzle, the fuel flow shuts off. This prevents fuel from spilling out of the fuel filler tube.

If there is a restriction or blockage in the venting path, an early fuel shut off condition will be present. A vehicle can experience a hard to fill condition for one of the following reasons:

1. Fuel nozzle sensitivity
2. Fuel Tank Isolation Valve (FTIV) is not open
3. There is a blockage in the tank venting
4. There is a blockage in the venting on the fresh air side of the system
5. Kinked or restricted fuel fill hose and fill tube

The following diagnostic procedure should help to determine which issue is causing the hard to fill condition.

Courtesy of CHRYSLER GROUP, LLC

DIAGNOSTIC PROCEDURE: 

1. Ask the customer the following question: If the early shut off condition is only present at certain stations, happens consistently after the first few seconds of fueling, or stops after repositioning the nozzle, the issue is most likely due to a nozzle sensitivity issue. The only other possible issue could be if the Inlet Check Valve is stuck or sticking and not allowing fuel to flow freely into the tank. If the condition happens regular at multiple stations, or after a few gallons are filled, it is most likely a venting issue. Continue diagnosing in step 2.
   1. Is the condition present at only one station or multiple gas stations?
   2. Does the nozzle turn off immediately after a few seconds or after a few gallons?
   3. If you pull the nozzle out slightly or turn the nozzle to different positions does the early shut off condition stop?
   4. How long was the time from pressing the refuel button to fueling? The FTIV will time out after approximately 20 minutes from when the Refuel button is pressed.
2. Some of the conditions that can cause a hard to refuel condition will also set other evaporative system faults. Use the scan tool to check for any evaporative system DTCs. If DTCs are present perform the DTC diagnostic procedure first before continuing. If no DTCs are present, continue diagnosing in step 3.
3. If equipped with a capless fuel filler,  use the emergency funnel to inspect both doors, and the filler tube for any foreign objects or debris. Verify the doors can open and close properly. A bore scope may be used to inspect inside the filler tube. If the capless doors are damaged or any obstructions are found the entire fill tube assembly should be replaced. If there are no obstructions/damage or the vehicle does not have a capless fuel filler, continue diagnosing in step 4.
4. Raise the vehicle and visually inspect for a kinked or pinched Filler Tube, Recirc Tube, and the tubes that connect between the Fuel Tank, FTIV, Charcoal Canister and ELCM. Repair or replace any obvious issues. If the tubes appear ok, continue diagnosing in step 5.
5. This step is designed to split the system between the tank side and fresh air side.  The fuel level should be low enough to allow enough fuel to be put into the vehicle to make a proper determination (example: less than 1/2 tank). Also, do not refill from a storage tank. Use a gas station filling pump to refill. Disconnect the Fuel Tank side vent tube at the FTIV. Attempt to refill the vehicle.
   1. If fuel flows freely without early shut off, the issue is with the fresh air side of the system (FTIV, Canister or ELCM/filter). Continue diagnosing in step 7.
   2. If the early fuel shut off condition is still occurring, the issue is with the tank side of the system (LVS or Recirc Tubing). Continue diagnosing in step 6.
6. Disconnect the Recirc line at the Fuel Tank or Fuel Filler Tube and attempt to refill.
   1. If fuel flows freely without early shut off, replace or clear the Recirc Tube or check for an obstruction in the Recirc Tube portion of the fill tube.
   2. If early fuel shut off is still occurring, drain the fuel from the tank, remove the fuel filler hose and check for an obstructed or hard to open Inlet Check Valve. If the Inlet Check Valve is not obstructed and opens freely, the LVS is restricted and will require replacement. Replace the Fuel Tank or Fuel Pump assembly depending on the LVS location in the system.
   NOTE:

   On some vehicles the LVS is welded into the Fuel Tank. On other vehicles the LVS is part of the Fuel Pump Assembly. If the LVS is not visible on the tank or pump, it is mounted inside the Fuel Tank. If the LVS is mounted on the Fuel Pump Module, it should be replaced before replacing the Fuel Tank.

7. Raise the vehicle and disconnect both of the FTIV lines. Press the fuel door release button. Apply controlled air (5 psi) through the FTIV.
   1. If there is no air flow through the FTIV, verify that fuel door switch the is commanding the FTIV open. Check the input voltage and ground circuits, If no issues are found, replace the FTIV.
      NOTE:

      In some situations, such as when the fuel filler door is manually opened, the FTIV will remain closed unless the ignition is in the on position (engine not running). When the PCM sees the fuel filler door switch as open, it opens the FTIV to allow venting of the tank. A closed FTIV prevents fuel vapors from exiting the fuel tank creating additional back pressure.

   2. If air flows freely, continue diagnosing in step 8.
8. Reconnect the vent tube to the FTIV. Disconnect the vent tube that connects between the Charcoal Canister and the ELCM at either component. Apply controlled air (5 psi) through the ELCM.
   1. If air is flowing freely, replace the Charcoal Canister if the vent tubes are not obstructed.
   2. If the air does not flow freely, Remove the air filter from the ELCM and apply controlled air again.
      • If the air still does not flow freely, replace the ELCM.
      • If the air does flow freely, replace the air filter.