Fuel Gauge: Description and Operation
FUEL GAUGEDESCRIPTION
A fuel gauge is standard equipment on all instrument clusters. The fuel gauge is located in the lower right corner of the instrument cluster, to the right of the speedometer. The fuel gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 45 degree scale on the cluster overlay that reads left-to-right from "F" (or Full) to "E" (or Empty). An International Control and Display Symbol icon for "Fuel" is located on the cluster overlay, directly to the left of the low end of the scale.
The fuel gauge graphics are white against a black field, making them clearly visible within the instrument cluster in daylight. When illuminated from behind by the panel lamps dimmer controlled cluster illumination lighting with the exterior lamps turned On, the white graphics appear amber. The orange gauge needle is internally illuminated. Gauge illumination is provided by Light Emitting Diode (LED) units soldered onto the instrument cluster electronic circuit board. The fuel gauge is serviced as a unit with the instrument cluster.
OPERATION
The fuel gauge gives an indication to the vehicle operator of the level of fuel in the fuel tank. This gauge is controlled by 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 fuel gauge is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board when the instrument cluster detects that the ignition switch is in the On position. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off position. The instrument cluster circuitry controls the gauge needle position and provides the following features:
- Fuel Level Sensor Input (At Ignition On): When the cluster detects the ignition switch has been turned to the On position, the cluster moves the gauge needle to the proper relative position on the gauge scale as signaled by the fuel level sensor without any electronic damping.
- Fuel Level Sensor Input (After Ignition On): After the ignition switch has been turned to the On position, the cluster applies an algorithm to the input from the fuel level sensor to electronically dampen gauge needle movement against the negative effect that fuel sloshing within the fuel tank can have on accurate gauge readings.
- Fuel Level Sensor Input Open: If the fuel level sensor input to the instrument cluster is an open circuit, the cluster will move the fuel gauge needle to the "E" (Empty) position on the gauge scale, but the low fuel indicator will not be illuminated.
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. 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. As the fuel level decreases, the resistance through the fuel level sensor increases. 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 diagnostic scan tool is required. Refer to the appropriate diagnostic information.