The ECM monitors the fuel tank internal pressure using the vapor pressure sensor. The ECM supplies the sensor with a regulated 5 V reference voltage, and the sensor provides the ECM with a signal voltage of between 0.5 V and 4.5 V as feedback, according to the pressure level in the fuel tank.
When the pressure in the fuel tank is low, the output voltage of the vapor pressure sensor is low. When it is high, the output voltage is high. If the output voltage of the vapor pressure sensor is outside the normal range, the ECM determines that there is a malfunction in the sensor or sensor circuit.
When the internal pressure indicated by the vapor pressure sensor drops below -3.999 kpa (-30 mmHg), or rises above 1.999 kpa (15 mmHg), the ECM interprets this as a malfunction in the sensor, and illuminates the MIL and sets a DTC.