Fuel Gauge
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 CCN circuit board based upon programming and a hard wired input received from the fuel level sending unit on the fuel pump module in the fuel tank.
The fuel gauge is a stepper motor design gauge that receives battery current on the CCN electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the On or Start positions. The CCN 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 CCN circuitry controls the gauge needle position and provides the following features:
- Fuel Level Message - The TIPM 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 TIPM then sends the appropriate electronic fuel level messages to the CCN. The CCN programming applies an algorithm to calculate the proper fuel gauge needle position based upon the fuel level message input, then moves the gauge needle to the proper relative position on the gauge scale. This algorithm is used to dampen gauge needle movement against the negative effect that fuel sloshing within the fuel tank can have on accurate inputs from the fuel tank sending unit to the TIPM.
- Less Than 11 Percent Tank Full Message - Each time the fuel level message to the CCN indicates 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 about the one-sixteenth graduation 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 message indicates 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 TIPM.
- Less Than Empty Stop Message - Each time the CCN 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 TIPM is a short circuit.
- More Than Full Stop Message - Each time the CCN 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 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 TIPM is an open circuit.
The CCN continually monitors the fuel tank sending unit to determine the level of fuel in the fuel tank. The CCN then sends the proper fuel level messages to other electronic modules in the vehicle over the CAN data bus. For further diagnosis of the fuel gauge or the CCN circuitry that controls the gauge, refer to DIAGNOSIS AND TESTING . The fuel gauge is serviced as a unit with the instrument cluster.