Dodge ram truck 3500 1996 Service Manual page 1315

B R
FUEL SYSTEM 14 - 81
D I A G N O S I S &M® T E S T i ^ Q feogitiBisuecF.)
FUEL HEATER TEST
The fuel heater is used to prevent diesel fuel from
waxing during cold weather operation.
NOTE: The fuel heater element, fuel heater relay
and fuel heater temperature sensor are not con­
trolled by the powertrain control module (PCM).
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 rev­
ving up. I t can also cause blue or white fog-like
exhaust. I f the heater is not operating in cold tem­
peratures, the engine may not operate due to fuel
waxing.
The fuel heater is located on the left side of the
engine above the starter motor (Fig. 28).
FUEL TEMPERATURE SENSOR
FUEL
TRANSFER
PUMP
ELECTRICAL
CONNECTOR
J9414-94
FUEL
HEATER
Fig. 28 Fuel Heater Location
The heater assembly is equipped with a built-in
fuel temperature sensor (thermostat) (Fig. 29) or
(Fig. 28) that senses fuel temperature. When the fuel
temperature is below 40 degrees F, the sensor allows
current to flow to the built-in heater element to
warm the fuel. When the fuel temperature is above
80 degrees F, the sensor stops current flow to the
heater element (circuit is open).
Voltage to operate the fuel heater element is sup­
plied from the ignition switch, through the fuel
heater relay (Fig. 3 0 )
(also refer to Fuel Heater
Relay), to the fuel temperature sensor and on to the
fuel heater element. « ,
FROM FUEL
TANK
TO FUEL
TRANSFER
PUMP
FUEL
TEMPERATURE
^ SENSOR
PRE-FILTER
SCREEN
v
MOUNTING
BRACKET/
SPACER
MACHINED
HEX
FUEL HEATER
ASSEMBLY
J9414-95
Fig. 29 Fuel Heater Assembly
FUEL SHUT-OFF
FUEL HEATER SOLENOID RELAY
RELAY j
BRAKE MASTER
CYLINDER
Fig. 80 Fuel Heater Relay—Diesel
The built-in heater element operates on 12 volts,
300 watts at 0 degrees F. As temperature increases,
power requirements decrease.
The fuel heater assembly contains a pre-filter (Fig.
29) to prevent contaminants from entering the fuel
transfer pump.
A minimum of 7 volts is required to operate the
fuel heater. The resistance value of the heater ele­
ment is less than 1 ohm (cold) and up to 1000 ohms
warm.
TESWIMG
(1) Remove the electrical connector at the side of
the fuel heater (Fig. 28).
(2) Using an ohmmeter, check the resistance
across the two terminals on the side of the heater.