Fungi and other microorganisms can survive and multiply in diesel fuel if water is present. The fungi can be present in any part of the fuel handling system. These fungi grow into long strings and will form into large globules. The growths appear slimy and are usually black, green, or brown. The fungi may grow anywhere in the fuel but are most plentiful where diesel fuel and water meet. As the fuel is agitated (when service station tanks are being filled), fungi are distributed throughout the tank and may be pumped into a vehicle.

Fungi use the fuel as their main energy supply and need only trace amounts of water and minerals. As they grow and multiply, they change fuel into water, sludge, acids, and products of metabolism. The most common symptom is fuel filter plugging; however, various metal components (fuel tank, pipes, and injection pump) can corrode.

Caution: Avoid physical contact with the biocides in order to avoid personal injury.

This procedure checks for the presence of water and gasoline in the diesel fuel that may cause the injection pump and the nozzle to incur damage.

1. Remove the fuel filter element.
2. Inspect the fuel filter element.

•	If water, gasoline or fungi/bacteria are not present, end the inspection.

•	If water or fungi/bacteria are present, Go to Cleaning Water from the Fuel System.

•	If gasoline is present, Go to Cleaning Gasoline from the Fuel System.

Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

1. Disconnect the batteries.
2. Drain the fuel tank.
3. Remove the fuel tank. (Refer to Fuel Tank Replacement).
4. Remove the fuel sender unit. (Refer to Fuel Sender Assembly Replacement ).
5. Inspect the fuel tank and the fuel sender for rust, fungi or bacteria.
6. Clean the inside of the fuel tank and the fuel sender with hot water.
7. Dry the fuel tank and the fuel sender with compressed air.
8. Disconnect the ends of the following lines.

•	The lift pump suction line

•	The lift pump feed line

•	The fuel filter outlet line

•	The fuel filter drain line

•	The fuel return line

9. Inspect each of the pipes and replace any rusted pipes.
10. Clean the inside of the fuel filter housing.
11. Dry the inside of the fuel filter housing with compressed air.
12. Dry the inside of each line with low pressure air.
13. Remove the FUEL SOL fuse from the fuse panel.
14. Install a new fuel filter element.
15. Install the fuel sender and the fuel tank (add clean diesel fuel to ¼ full).
16. Reconnect the following lines.

•	The lift pump suction (both ends) lines

•	The lift pump feed (both ends) lines

•	The fuel filter drain line

•	The fuel return (at injection pump) line

17. Connect the fuel filter outlet and the fuel return line at the fuel sender to the hoses that flow to the metal containers.
18. Connect the batteries.
19. Use the Scan Tool in order to command the lift pump ON.
20. Operate the lift pump until the clean fuel flows from the fuel filter outlet into a metal container.
21. Connect the hose from the fuel filter outlet to the injection pump inlet.
22. Open each injection line at each nozzle end.
23. Crank the engine until the clean fuel flows from it.

•	Use two wrenches when loosening the injection line fittings.

•	Allow a maximum of 15 seconds cranking time, followed by 1 minute of cranking motor cooling time.

24. Use two wrenches in order to tighten each injection line fitting at its nozzle.
25. Install the FUEL SOL fuse in the fuse panel.
26. Start the engine.
27. Allow the engine to run for 1 minute while the fuel flows from the fuel return line into a metal container.
28. Stop the engine.
29. Connect the fuel return hose to the fuel sender.
30. Clean the engine of fuel spillage.
31. Fill the fuel tank and add a biocide, if needed.

1. Drain the fuel tank.
2. Fill the fuel tank.
3. Remove the FUEL SOL fuse from the fuse panel.
4. Remove the fuel filter outlet.
5. Connect the fuel filter outlet to a hose that flows to a metal container.
6. Use a scan tool in order to command the lift pump ON until the clean fuel flows from the fuel filter outlet into a metal container.
7. Connect the hose from the fuel filter outlet to the injection pump inlet.
8. Install the FUEL SOL fuse in the fuse panel.
9. Attempt to start and run the engine for 15 minutes (If the engine does not start, purge the injection system).
10. Stop the engine.
11. Clean the engine of fuel spillage.
12. Clear the engine DTCs.