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 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 coalesce, 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.

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
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

Check the Water in Fuel lamp for proper operation. Refer to Water in Fuel Indicator Malfunction (Water in Fuel Indicator Malfunction).

1. Turn ON the ignition , with the engine OFF.
2. Disconnect the fuel heater connector.
3. With the fuel temperature above 21°C (70°F), test for continuity between the ignition 1 voltage terminal and the fuel filter/heater element housing.

• If continuity was present, the thermostatic switch is stuck ON. Replace the fuel heater element.

Repair Instructions

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

Fuel Heater Replacement (Service and Repair)