Fuel Gauge: Description and Operation
FUEL LEVEL GAUGEA fuel gauge is standard equipment on all instrument clusters. The fuel gauge is located in the lower left corner of the instrument cluster, to the left of the tachometer. The fuel gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 90 degree scale on the gauge dial face that reads left-to-right from "E" (or Empty) to "F" (or Full). An International Control and Display Symbol icon for "Fuel" is located on the gauge dial face, directly below the right end of the gauge scale. An arrowhead pointed to the left side of the vehicle is imprinted on the gauge dial face next to the "Fuel" icon to provide the driver with a reminder as to the location of the fuel filler access.
The fuel gauge graphics are either white, gray and orange against a black gauge dial face (base cluster) or black and gray against a taupe gauge dial face (premium cluster), 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 base cluster white gauge graphics appear blue-green and the orange graphics still appear orange, while the premium cluster taupe gauge dial face appears blue-green with the black graphics silhouetted against the illuminated background. The gray gauge graphics for both versions of the cluster are not illuminated. The orange gauge needle in the base cluster gauge is internally illuminated, while the black gauge needle in the premium cluster gauge is not.
Base cluster gauge illumination is provided by replaceable incandescent bulb and bulb holder units located on the instrument cluster electronic circuit board. Premium cluster gauge illumination is provided by an integral electro-luminescent lamp that is serviced as a unit with the instrument cluster. The fuel gauge is serviced as a unit with the instrument cluster.
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 electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus. The fuel gauge is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (RUN/START) circuit whenever the ignition switch is in the On or Start positions. 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:
- Percent Tank Full Message - Each time the cluster receives a message from the PCM indicating the percent tank full, the cluster moves the gauge needle to the proper relative position on the gauge scale. The PCM applies an algorithm to the input from the fuel tank sending unit to dampen gauge needle movement against the negative effect that fuel sloshing within the fuel tank can have on accurate inputs to the PCM.
- Less Than 15 Percent Tank Full Message - Each time the cluster receives messages from the PCM indicating the percent tank full is less than 15, the gauge needle is moved to below the one-eighth position on the gauge scale and the low fuel indicator is illuminated. The low fuel indicator remains illuminated until the cluster receives messages from the PCM indicating that the percent tank full is greater than 15 (one-eighth), or until the ignition switch is turned to the Off position, whichever occurs first.
- Less Than Empty Percent Tank Full Message - Each time the cluster receives a message from the PCM indicating the percent tank full is less than empty, the gauge needle is moved to the far left (low) end of the gauge scale and the low fuel indicator is illuminated immediately. This message would indicate that the fuel tank sending unit input to the PCM is a short circuit.
- More Than Full Percent Tank Full Message - Each time the cluster receives a message from the PCM indicating the percent tank full is more than full, the gauge needle is moved to the far left (low) end of the gauge scale and the low fuel indicator is illuminated immediately. This message would indicate that the fuel tank sending unit input to the PCM is an open circuit.
- Communication Error - If the cluster fails to receive a percent tank full message, it will hold the gauge needle at the last indication for about twelve seconds or until the ignition switch is turned to the Off position, whichever occurs first. After twelve seconds, the cluster will move the gauge needle to the low end of the gauge scale.
- Actuator Test - Each time the cluster is put through the actuator test, the fuel gauge needle will be swept across the entire gauge scale and back in order to confirm the functionality of the gauge and the cluster control circuitry
The PCM continually monitors the fuel tank sending unit input to determine the level of fuel in the fuel tank. The PCM then applies an algorithm to the input and sends the proper percent tank full messages to the instrument cluster. For further diagnosis of the fuel gauge or the instrument cluster circuitry that controls the gauge,refer to Instrument Cluster Diagnosis and Testing. For proper diagnosis of the fuel tank sending unit, the PCM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the fuel gauge, a DRBIII scan tool is required. Refer to the appropriate diagnostic information