FUEL HEATER OPERATION
The fuel heater is used to prevent diesel fuel from waxing during cold weather operation. When the fuel temperature is below 45° ±8 F (7°C), the temperature sensor allows current to flow to the heater element warming the fuel. When the fuel temperature is above 75 0 ±8 F (24°C), the sensor stops current flow to the heater element. Battery voltage to operate the fuel heater element is supplied from the ignition switch and through a solid stated device in the TIPM. The fuel heater element and "solid state device in TIPM" are not computer controlled.The heater element operates on 12 volts, 300 watts at 0° F (-18° C).
DIAGNOSIS AND TESTING
FUEL HEATER
The fuel heater is used to prevent diesel fuel from waxing during cold weather operation.
NOTE: The fuel heater element, "solid state device in TIPM" is not controlled by the Engine Control Module (ECM).
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.
The fuel heater assembly is located on the side of the fuel filter housing and internal to the fuel filter housing. The heater assembly is equipped with a built-in fuel temperature sensor (thermostat) that senses fuel temperature. When fuel temperature drops below 45° ± 8° F (7° C), the sensor allows current to flow to the built-in heater element to warm fuel. When fuel temperature rises above 75 o± 8° F (24° C), the sensor stops current flow to heater element ( the circuit is open). Voltage to operate fuel heater element is supplied from the ignition switch, though solid state device in TIPM, to fuel
temperature sensor and on to fuel heater element. The heater element operates on 12 volts, 300 watts at 0 OF (-18° C). As temperature increases, power requirements decrease. A minimum of 7 volts is required to operate the fuel heater. The resistance value of the heater element is less than 1 ohm (cold) and up to 1000 ohms warm.
TESTING
1. Disconnect the electrical connector from the heater element. Ambient temperature must be below the circuit close temperature. If necessary, induce this ambient temperature by placing ice packs on a thermostat to produce an effective ambient temperature below circuit close temperature. Measure resistance across two pins. Operating range is 0.3 - 0.45 Ohms.
2. If resistance is out of range, replace heater element.