Sprinter 3500 L5-2.7L DSL Turbo (2004)
Low Fuel Lamp/Indicator: Description and Operation
A low fuel indicator is standard equipment on all instrument clusters. The low fuel indicator is located directly below the low end of the fuel gauge scale.
The low fuel indicator consists of a small triangular cutout in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay
prevents the indicator from being clearly visible when it is not illuminated. An amber Light Emitting Diode (LED) behind the cutout in the opaque layer
of the overlay causes the triangle to appear in amber through the translucent outer layer of the overlay when the indicator is illuminated from behind by
the LED, which is soldered onto the instrument cluster electronic circuit board. The low fuel indicator is serviced as a unit with the instrument cluster.
The low fuel indicator gives an indication to the vehicle operator when the level of fuel in the fuel tank becomes low. This indicator is controlled by a
transistor on the instrument cluster circuit board based upon cluster programming and a hard wired input received by the cluster from the fuel level
sensor in the fuel tank. The low fuel indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic
will only allow this indicator to operate when the instrument cluster detects that the ignition switch is in the On position. Therefore, the LED will always
be off when the ignition switch is in any position except On. The LED only illuminates when it is provided a path to ground by the instrument cluster
transistor. The instrument cluster will turn on the low fuel indicator for the following reasons:
-
Bulb Test - Each time the ignition switch is turned to the On position the low fuel indicator is illuminated for about two seconds as a bulb test.
-
Fuel Level Sensor Input - Each time the cluster receives an input from the fuel level sensor indicating that the fuel level has reached about 12 liters
(3 gallons) or less, the low fuel indicator is illuminated. The indicator remains illuminated until the cluster receives an input from the fuel level
sensor indicating that the fuel level is above 12 liters (3 gallons), or until the ignition switch is turned to the Off position, whichever occurs first.
The fuel level sensor in the fuel tank provides a hard wired input to the instrument cluster circuitry through the fuel level sense circuit. The fuel level
sensor is a potentiometer that changes resistance according to the fuel level. As the fuel level decreases, the resistance through the fuel level sensor
increases. The instrument cluster applies a fuel tank characteristic curve and fuel tank reserve valve setting to the fuel level sensor input, which must be
configured when the cluster is initialized. These characteristics determine the algorithm the cluster uses to display the fuel level data on the fuel gauge
and the control for the low fuel warning indicator. The fuel level sensor and the fuel level sense circuit to the instrument cluster can be diagnosed using
conventional diagnostic tools and methods. For proper diagnosis of the instrument cluster circuitry that controls the fuel gauge, a DRBIII(R) scan tool is
required. Refer to the appropriate diagnostic information.
