Fuel Heater Always On

FUEL HEATER ALWAYS ON

CIRCUIT DESCRIPTION
The fuel filter/heater element housing consists of the fuel heater, the water-in-fuel sensor, and a filter.

As fuel enters the fuel filter/heater element housing, it first passes though the fuel heater. The heater contains a thermostatic switch that turns the heater ON and OFF, depending on the temperature of the fuel. When the temperature is below 8°C (46°F), the heater is turned ON. When the temperature is above 15°C (59°F), the heater is turned OFF.

The fuel then passes through the fuel filter and the water separator, where the droplets of water combine into larger drops, then fall into the water reservoir located in the bottom of the filter.

When fuel flows from the fuel filter/heater element housing to the fuel injection pump, the fuel is clean and free of water.

TEST DESCRIPTION

Steps 1-5:

The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for a fuel heater thermostatic switch that is stuck ON.
3. This steps tests for a thermostatic switch that completes the circuit.