RAM 3500 Truck 4WD L6-5.9L DSL Turbo VIN C (2002)
Fuel Level Sensor: Description and Operation
FUEL LEVEL SENDING UNIT / SENSOR
The fuel gauge sending unit (fuel level sensor) is attached to the side of the fuel tank module. The sending unit consists of a float, an arm, and a
variable resistor track (card).
The fuel tank module on diesel powered models has 3 different circuits (wires). Two of these circuits are used at the fuel gauge sending unit for
fuel gauge operation. The other wire is used for a ground. The diesel engine does not have a fuel tank module mounted electric fuel pump. The
electric fuel pump (fuel transfer pump) is mounted to the engine.
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
sending unit. This is fed directly from the Powertrain Control Module (PCM). NOTE: For diagnostic purposes, this 12V power source can only be
verified with the circuit opened (fuel tank module electrical connector unplugged). With the connectors plugged, output voltages will vary from
about 0.6 volts at FULL, to about 7.0 volts at EMPTY 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 the appropriate fuel gauge level reading. Refer to Instrument Panel for additional
information.
