Fuel Heater Always On

FUEL HEATER ALWAYS ON

DIAGNOSTIC FAULT INFORMATION
Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
The diesel fuel conditioning module (DFCM) consists of a water separator, an electric prime pump, a 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 when the ignition is ON. The warmed fuel then passes through the fuel filters to the fuel injection pump.

CIRCUIT/SYSTEM TESTING
1. Inspect the water-in-fuel lamp for proper operation. Refer to Water-in-Fuel Lamp Always On. Water-in-Fuel Lamp Always On
2. Disconnect the fuel heater harness connector from the fuel DFCM housing.
3. Connect a DMM and test for continuity between the terminals of the fuel heater element.
4. Observing the Fuel Temperature parameter with a scan tool.
- If the fuel temperature is more than 15.5°C (60°F) and continuity is present, the thermostatic switch is stuck ON. Replace the DFCM.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests