The fuel tank sending unit consists of a float that rides on the surface of the fuel in the tank and a variable resistor controlled by the float arm. When voltage is supplied to the fuel gage, current flows through the gage to the variable resistor and then to ground. The position of the display is determined by the amount of current flowing through the gage. The fuel level sender signal circuit connects to the instrument panel cluster (IPC) and a splice in this circuit provides a signal to the engine control module (ECM).

As the fuel level decreases the sending unit resistance increases, and when the fuel level increases, the sending unit resistance decreases. The display of the correct fuel level is dampened slightly upon start-up, cycling of ignition, and will stabilize after approximately 12 seconds.

The ECM will not illuminate the malfunction indicator lamp (MIL).

Use the Freeze Frame and/or Failure Records data in order to locate an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data may aid in determining the number of miles since the DTC set. The Fail Counter and Pass Counter can also aid in determining the number of ignition cycles that the diagnostic reported a pass and/or fail. Operate the vehicle within the same freeze frame conditions (RPM, engine load, vehicle speed, temperature, etc.). This will isolate when the DTC failed. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

The number below refers to the step number on the diagnostic table.

3. This test determines whether the open is in the fuel level signal circuit or if there is an internal engine control module problem.

5. Clear all DTCs within the ECM after performing this diagnostic table.