The diesel fuel conditioning module (DFCM) consists of a water separator, an electric prime pump, fuel heater element and a filter element . Fuel is heated by passing through the fuel heater element, which is operated by a built-in thermostatic switch. The thermostatic switch turns the heater element ON and OFF , depending on the fuel temperature. The fuel heater element has voltage anytime the ignition is turned on. The warmed fuel then passes through the fuel filters to the fuel injection pump.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

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 fuel DFCM 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 open or short to ground on the ignition 1 voltage circuit .

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

⇒	If the test lamp did not illuminate repair the open in the ground circuit.

5. 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 from the DFCM housing.
2. Remove the DFCM housing from the vehicle.
3. Connect a DMM between the ignition 1 voltage circuit and the ground circuit of the fuel heater.
4. Cool the thermostatic switch of the fuel heater with ice or refrigeration.
5. Observe the DMM for continuity.

⇒	If the thermostatic switch does not turn and complete the circuit when the temperature is between -8.4°C to +15.4°C (+16.9°F to +59.8°F) replace the DFCM housing.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Primary Fuel Filter Replacement