Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

The fuel level sensor changes resistance in response to the fuel level. The engine control module (ECM) monitors the signal circuit of the fuel level sensor in order to determine the fuel level. When the fuel tank is full, the sensor resistance is low and the ECM senses a low signal voltage. When the fuel tank is empty, the sensor resistance is high and the ECM senses a high signal voltage. The ECM uses the signal circuit of the fuel level sensor in order to calculate the percentage of remaining fuel in the tank. The ECM sends the fuel level percentage via the GMLAN serial data circuit to the instrument panel cluster (IPC). The ECM sends the fuel information to the instrument panel cluster via the GMLAN serial data circuit in order to control the fuel gage and display the fuel level. Then fuel information is also used for evaporative emission (EVAP) and other OBD diagnostics.

Schematic Reference

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

Scan Tool Data List

1. Ignition OFF, disconnect the harness connector at the fuel level sensor. Install a signal generator and instrument panel tester between the signal circuit and the low reference circuit.
2. Ignition ON, vary the resistance on the signal generator from 40 ohms - 250 ohms. With the scan tool verify that the Fuel Tank Level Remaining parameter displays the correct fuel level percent. Refer to Fuel Level Specifications .

⇒	If the fuel level percent is incorrect, test the signal circuit and the low reference circuit for an open/high resistance. If all circuit tests normal, replace the ECM.

3. Ignition ON, vary the resistance on the signal generator from 40 ohms - 250 ohms. Observe the fuel gage and verify that the fuel gage displays the correct fuel level. Refer to Fuel Level Specifications .

⇒	If the fuel gage display is incorrect, test or replace the fuel gage.

4. If all circuits test normal, test or replace the fuel level sensor.

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.