Fuel Level Sending Unit / Sensor Description; Operation - Chrysler Vehicle User Manual

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FUEL FILTER/PRESSURE REGULATOR (Continued)
Fig. 2 Fuel Filter/Fuel Pressure Regulator Gasket
1 - TOP OF MODULE
2 - GASKET
Fig. 3 Fuel Filter/Fuel Pressure Regulator
1 - FUEL FILTER/FUEL PRESSURE REGULATOR
2 - TO FUEL INJECTORS
3 - FUEL SUPPLY TUBE
4 - O-RINGS
5 - FUEL INLET FROM PUMP
6 - FUEL RETURN TO TANK
(3) Apply a small amount of clean engine oil to
o-rings. Do not install o-rings separately into
fuel pump module. They will be damaged when
installing filter/regulator.
(4) Install new gasket to top of fuel pump module.
(5) Press new filter/regulator into top of pump
module until it snaps into position (a positive click
must be heard or felt).
(6) The molded arrow (Fig. 1) on top of fuel pump
module should be pointed towards front of vehicle (12
o'clock position).
(7) Rotate filter/regulator until fuel supply tube
(fitting) is pointed to 10 o'clock position.
(8) Install new retainer clamp (clamp snaps over
top of filter/regulator and locks to flanges on pump
module).
(9) Connect fuel line at filter/regulator. Refer to
Quick-Connect Fittings in this group for procedures.
(10) Install fuel tank. Refer to Fuel Tank Removal/
Installation.
FUEL LEVEL SENDING UNIT /
SENSOR
DESCRIPTION
The fuel gauge sending unit (fuel level sensor) is
attached to the side of the fuel pump module. The
sending unit consists of a float, an arm, and a vari-
able resistor track (card).

OPERATION

The fuel pump module has 4 different circuits
(wires). Two of these circuits are used for the fuel
gauge sending unit for fuel gauge operation, and for
certain OBD II emission requirements. The other 2
wires are used for electric fuel pump operation.
For Fuel Gauge Operation: A constant input
voltage source of about 12 volts (battery voltage) is
supplied to the resistor track on the fuel gauge send-
ing unit. This is fed directly from the Powertrain
Control Module (PCM). NOTE: For diagnostic pur-
poses, this 12V power source can only be veri-
fied with the circuit opened (fuel pump module
electrical connector unplugged). With the con-
nectors plugged, output voltages will vary from
about 0.6 volts at FULL, to about 8.6 volts at
EMPTY (about 8.6 volts at EMPTY for Jeep
models, and about 7.0 volts at EMPTY for
Dodge Truck models). The resistor track is used to
vary the voltage (resistance) depending on fuel tank
float level. As fuel level increases, the float and arm
move up, which decreases voltage. As fuel level
decreases, the float and arm move down, which
increases voltage. The varied voltage signal is
returned back to the PCM through the sensor return
circuit.
Both of the electrical circuits between the fuel
gauge sending unit and the PCM are hard-wired (not
multi-plexed). After the voltage signal is sent from
the resistor track, and back to the PCM, the PCM
will interpret the resistance (voltage) data and send
a message across the multi-plex bus circuits to the
instrument panel cluster. Here it is translated into
FUEL DELIVERY 14 - 5