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 the main energy supply. The fungi need only trace amounts of water and minerals. As the fungi grow and multiply, the fungi change fuel into water, sludge, acids, and products of metabolism. The most common symptom of contamination is fuel filter plugging. However, corrosion of metal components such as the fuel tank, pipes, and the injection pump may also be present.

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

This procedure inspects for the presence of water and gasoline in the diesel fuel that can damage the injection pump and the nozzle. To inspect for fuel contamination, perform the following:

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, drain the water from the fuel system.

•	If gasoline is present, refer 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.
4. Remove the fuel sender unit.
5. Inspect the fuel tank and the fuel sender for rust, fungi, or bacteria. Replace if rust is found.
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 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. Install a new fuel filter element.
14. Install the fuel sender and the fuel tank.
15. Add clean diesel fuel to ¼ full.
16. Reconnect the following lines:

•	The lift pump suction lines at both ends

•	The lift pump feed lines at both ends

•	The fuel return line at injection pump

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. Command the lift pump ON with a scan tool.
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.

Important: Open all lines at the same time. This will prevent the engine from starting.

22. Open each injection line at each nozzle end.
23. Crank the engine until the clean fuel flows from the injection nozzle lines.

•	Use 2 wrenches when loosening the injection line fittings.

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

24. Use 2 wrenches in order to tighten each injection line fitting at the nozzle.
25. Start the engine.
26. Allow the engine to run for 1 minute while the fuel flows from the fuel return line into a metal container.
27. Stop the engine.
28. Connect the fuel return hose to the fuel sender.
29. Clean the engine of fuel spillage.
30. Fill the fuel tank and add a biocide, if needed.

1. Drain the fuel tank.
2. Fill the fuel tank.
3. Remove the fuel filter outlet.
4. Connect the fuel filter outlet to a hose that flows to a metal container.
5. Command the lift pump ON until the clean fuel flows from the fuel filter outlet into a metal container with a scan tool.
6. Connect the hose from the fuel filter outlet to the injection pump inlet.
7. Attempt to start and run the engine for 15 minutes. If the engine does not start, purge the injection system.
8. Stop the engine.
9. Clean the engine of fuel spillage.
10. Clear the engine DTCs.