Circuit Description

The primary fuel level sensor and the secondary fuel level sensor changes resistance in response to the fuel level. The powertrain control module (PCM) monitors the signal circuit of the primary fuel level sensor and the secondary fuel level sensor in order to determine the fuel level. When the fuel tanks are full, the resistance of both fuel level sensors are high and the PCM senses a high signal voltage on both the signal circuits of the primary fuel level sensor and the secondary fuel level sensor. When the fuel tanks are empty, the resistance of the fuel level sensors are low and the PCM senses a low signal voltage. The PCM uses the signal circuits of the primary fuel level sensor and the secondary fuel level sensor in order to calculate the percentage of remaining fuel in the tank. The PCM sends the fuel level percentage via the class 2 serial data circuit to the instrument cluster in order to control the fuel gage. The fuel level information is also used for misfire and evaporative emission (EVAP) diagnostics.

This diagnostic tests for a lower than normal secondary fuel level sensor signal.