Fuel Heater Always On

Fuel Heater Always On

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.

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.

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Circuit/System Testing

1. Inspect the water-in-fuel lamp for proper operation. Refer to Water in Fuel Indicator Malfunction (Water in Fuel Indicator Malfunction).
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

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Primary Fuel Filter Replacement (Primary Fuel Filter Replacement)