The fuel filter/heater element housing consists of a water separator, a hand prime pump, fuel heater element and a filter element . Fuel passes through the fuel heater, which is operated by a built-in thermostatic switch. The thermostatic switch opens or closes to turn the heater ON or OFF, depending on temperature. Fuel then passes through the filter and the water coalescer, where the droplets of water in the fuel combine into larger drops that fall into the water reservoir in the filter. When fuel flows to the fuel injection pump, the fuel is clean and free of water.

Schematic Reference

Engine Controls Schematics

Electrical Information Reference

Check the Water in Fuel lamp for proper operation. Refer to Water-in-Fuel Lamp Always On .

1. Disconnect the fuel heater harness connector from the top of the fuel filter/heater element housing.
2. Turn ON the ignition with the engine OFF.
3. Probe the fuel heater ignition 1 voltage circuit with a test lamp connected to a good ground.

⇒	If the test lamp did not illuminate repair the short to ground or open in the ignition 1 voltage circuit .

4. Probe the fuel heater ground circuit at the fuel filter/heater element housing with a test lamp connected to battery voltage.

⇒	If the test lamp did not illuminate repair the open in the ground circuit between the fuel filter/heater element housing and the engine ground.

5. Remove the fuel filter from the fuel filter/heater element housing. Test the ignition 1 voltage circuit and the ground circuit for an open in the fuel filter/heater element housing.

⇒	If either circuit tested open replace the fuel heater element.

6. If all circuits test normal, test the fuel heater thermostatic switch for proper operation. Refer to Component Testing in this diagnostic.

1. Remove the fuel filter/heater element housing from the vehicle.
2. Connect the ignition 1 voltage circuit of the fuel heater to a battery voltage source and connect the ground circuit of the fuel heater to a ground.
3. Cool the thermostatic switch of the fuel heater with ice.
4. Observe the heating element.

⇒	If the thermostatic switch does not turn on the heater element when the temperature is between -8.4°C and +15.4°C (+16.9°F and +59.8°F) replace the fuel heater element.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Heater Replacement