Low Fuel Indicator

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 IPC circuit board based upon IPC programming and electronic fuel level  messages received by the IPC from the BCM over the CAN data bus.

The low fuel indicator LED is completely controlled by the IPC logic circuit, and that logic will only allow this indicator to operate when the IPC receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED will always be OFF when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by the IPC transistor. Each time the ignition switch is turned to the ON position the low fuel indicator is illuminated for about three seconds as a bulb test. The IPC will turn ON the low fuel indicator for the following reasons:

• Less Than 11 Percent Tank Full Message  - The BCM provides a constant current source to the fuel level sending unit and monitors a return input on a fuel level sense circuit. The resistance through the fuel level sending unit increases as the fuel level rises and decreases as the fuel level falls causing changes in the fuel level sense input voltage. The BCM then sends the appropriate electronic fuel level  messages to the IPC. Each time the fuel level messages to the IPC indicate the fuel tank is about 11 percent full or less for 10 consecutive seconds and the vehicle speed is zero, or for 60 consecutive seconds and the vehicle speed is greater than zero, the gauge needle is moved to the appropriate position on the gauge scale, the low fuel indicator is illuminated, and a single chime tone is sounded. The low fuel indicator remains illuminated until the fuel level messages indicate that the fuel tank is greater than about 14 percent full for 10 consecutive seconds and the vehicle speed is zero, or for 60 consecutive seconds and the vehicle speed is greater than zero, or until the ignition switch is turned to the OFF position, whichever occurs first. The chime tone feature will only repeat during the same ignition cycle if the low fuel indicator is cycled OFF and then ON again by the appropriate messages from the BCM.
• Less Than Empty Stop Message  - Each time the IPC receives a fuel level message indicating the fuel level in the fuel tank is less than the E  (or Empty) gauge needle stop position for five consecutive seconds, the gauge needle is moved to the low end of the gauge scale and the low fuel indicator is illuminated immediately. This input would indicate that the fuel level sense input to the BCM is a short circuit.
• More Than Full Stop Message  - Each time the IPC receives a fuel level message indicating the fuel level in the fuel tank is more than the F  (or Full) gauge needle stop position for ten consecutive seconds, the gauge needle is moved to the low end of the gauge scale and the low fuel indicator is illuminated immediately. This input would indicate that the fuel level sense input to the BCM is an open circuit.

The BCM continually monitors the fuel tank sending unit to determine the level of fuel in the fuel tank. The BCM then sends the proper electronic fuel level  message to the IPC and other electronic modules in the vehicle over the CAN data bus. The BCM will store a DTC for any fault detected in the fuel level sense circuit.