K 2500 Truck 4WD V8-393 6.5L DSL VIN P (1995)
Fuel Heater Functional Check
CIRCUIT DESCRIPTION
The fuel manager/filter assembly consists of the fuel heater, the water in fuel sensor, and a filter. The filter contains the "coalescer" the device that
combines small droplets of water into larger ones) and the filter/separator.
A fuel lift pump delivers diesel fuel front the tank to the fuel filter. As fuel enters the filter, it passes first through the fuel heater. The heater
contains a thermostatic switch. The switch opens or closes to turn the heater "OFF" or "ON," depending on the temperature of the fuel.
The fuel then passes through the filter. Next the fuel flows through the water coalescer. Here the droplets of water in the fuel are combined into
larger drops, the drops fall to the water reservoir in the filter. When fuel flows from the fuel manager/filter assembly to the injection pump, it is
clean and free of water.
The solid-state water in fuel sensor supplies voltage to a probe. When the probe touches water, the module closes a switch. This completes a
circuit to ground to light the "Water in Fuel" lamp. A time delay circuit in the water in fuel module grounds the lamp briefly to test the bulb each
time the system is turned "ON."
The fuel heater is operated by a built-in thermostatic switch. The thermostatic switch completes the circuit for the fuel heater element when it
senses a temperature below 8°C (46°F).
CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step checks to see if fuel heater is stuck "ON."
2. This checks to see if the thermostatic switch completes the circuit.
