Electrical Maintenance
91
Ultrasonic Fuel Level Sensor
The ultrasonic fuel level sensor (if used) is
mounted to a flange on top of the fuel tank. The
ultrasonic fuel level sensor consists of a sensor, a
sensor tube (or focus tube), and two gaskets. The
sensor is a transducer that emits ultrasonic sound
waves. The sound waves reflect off the fuel in the
sensor tube and return to the transducer. The
transducer senses the reflected sound waves and
determines the fuel level in the sensor tube.
Ultrasonic fuel level sensors are calibrated for use
with fuel tanks of particular size and shape. Refer
to the appropriate unit Parts Manual for the
correct part numbers.
The ultrasonic fuel level sensor and the fuel gauge
on the end of the fuel tank measure the fuel level
differently. The ultrasonic fuel level sensor
measures the actual volume of fuel in the tank.
The fuel gauge measures the height of the fuel in
the tank. Therefore, the fuel level at which fuel
level sensor reading and the fuel gauge reading
agree closely is at 50% or 1/2 full. The readings at
other fuel levels may not agree as closely. If you
think the ultrasonic fuel level sensor is not
working correctly, the best thing to do is to check
the output voltage as shown in step 4 below. The
output voltage should be between approximately
1.0 Vdc for an empty tank to 4.0 Vdc for a full
tank.
Check the operation of the fuel level sensor as
follows:
1. Use the
G
AUGES
soft key to display the Fuel
Level Sensor reading and compare it to the
reading of the fuel gauge on the end of the fuel
tank. The Fuel Level Sensor reading should be
approximately 50% when the fuel gauge reads
1/2 full.
2. Check to make sure that the Fuel Sensor Type
is set to Solid State in Unit Configuration in
the Guarded Access Menu.
3. Turn the unit on and check the for battery
voltage (12 Vdc) between the 8F (J1-1 pin)
and FUELN (J1-3 pin) wires in the
main/unified harness at the J1 connector on
the base controller. This is the input voltage. If
battery voltage is not present, check the
microprocessor.
4. If battery voltage is present, check the output
voltage between the FUEL (J1-2 pin) and
FUELN (J1-3 pin) wires in the main/unified
harness at the J1 connector on the base
controller. The voltage should be between 1
and 4 Vdc depending on the fuel level as
shown the following table.
NOTE: The output voltages listed above are
for the ultrasonic fuel level sensor designed
to be used with the SR-2, SR-3, and SR-4
Controllers. Other systems such as third
party telematics systems may use sensors
with slightly different output voltages. Refer
to the sensor specifications for those sensors.
1.
Ultrasonic Fuel Level Sensor
2.
Gaskets
3.
Sensor Tube
4.
Sensor Cable
Figure 157: Fuel Level Sensor
2
1
3
4
Fuel Level
Output Voltage
Empty
Approximately 1.0 Vdc
1/2 Full
Approximately 2.5 Vdc
Full
Approximately 4.0 Vdc
