Circuit Description

PCM monitors the resistance of fuel level sensor (tank sensor), calculates the amount of fuel in the tank, and provide a Pulse Width Modulated (PWM) ground to control the fuel gauge. The duty cycle increases to move the gauge to full (86 percent) and decreases (15 percent) to command empty. During the 3 second key-on bulb check, PCM commands the fuel gauge to zero percent duty cycle and activates the LOW FUEL light. The diagnostic test is performed only when the gauge is commanded to a zero percent duty cycle (e.g., during key-on bulb check period or if DTC P0462  or P0463 is set). DTC P0656 will set if the commanded duty cycle is zero and the output feedback is low (should be high/ignition voltage).

DTC P0656 will set if the commanded duty cycle is zero percent and output feedback is less than 3 volts for longer than one second. If output voltage is shorted to battery voltage, fuel gauge will be forced to zero percent duty cycle and the LOW FUEL light state (on/off) will depend on actual fuel level.