Fuel Heater: Testing and Inspection

A malfunctioning fuel heater can cause a wax build-up in the fuel filter/water separator. Wax build-up in the filter/separator can cause engine starting problems and prevent the engine from revving up. It can also cause blue or white fog-like exhaust. If the heater is not operating in cold temperatures, the engine may not operate due to fuel waxing.

Fuel Heater And Temperature Sensor Location:

1. Remove the electrical connector at the side of the fuel heater.
2. Using an ohmmeter, check the resistance across the two terminals on the side of the heater. Resistance should be approximately 1 ohm (cold) to 1000 ohms (warm).

Fuel Heater Assembly:

3. With the electrical connector still unplugged from the fuel heater, check the electrical operation of the fuel temperature sensor. Proceed to next step:
4. Using an ohmmeter, check the resistance across the two terminals in the pigtail wire harness coming from the fuel temperature sensor. The sensor circuit should be open if the fuel temperature is above 80 degrees. The sensor circuit should be closed if the fuel temperature is below 40 degrees.
5. Check for 12 volts at the disconnected temperature sensor connector with the ignition key ON.
6. With ignition ON, check for 12 volts at the fuel heater relay connector.

Fuel Heater Relay:

7. Check operation of the fuel heater relay.