Fuel Gage Inaccurate or Inoperative

Fuel Gage Inaccurate or Inoperative

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle Initial Inspection and Diagnostic Overview






Circuit/System Description

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

Circuit/System Testing

1. Ignition ON, with the scan tool installed, perform the IPC Gage Sweep Test in the IPC Output controls. Verify the fuel gage moves from the minimum position to the maximum position and back to the minimum position.

• If the gage does not perform the IPC Gage Sweep Test correctly, replace the IPC.

2. Ignition OFF, disconnect the harness connector at the primary (left) or secondary (right) fuel level sensor. Install a signal generator and the instrument panel tester between the signal circuit and the low reference circuit of the primary (left) or secondary (right) fuel level sensor.
3. Ignition ON, vary the resistance on the signal generator from 40 ohms - 250 ohms. With the scan tool verify that the Fuel Level Sensor Left Tank or Fuel Level Sensor Right Tank voltage parameter displays the correct voltage levels as the resistance is varied from 40 - 250 ohms. Refer to Fuel Level Specifications.

• If the Fuel Level Sensor Left Tank or Fuel Level Sensor Right Tank parameter is incorrect, test the signal circuit and the low reference circuit for an open/high resistance. If all circuit tests normal, replace the ECM.

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

Repair Instructions

Important: Always perform the Diagnostic Repair Verification Verification Tests

* Fuel Level Sensor Replacement - Left Side for the 6.0L engine
* Fuel Level Sensor Replacement - Right Side for the 6.0L engine
* Fuel Level Sensor Replacement - Left Side for the 7.0L engine
* Fuel Level Sensor Replacement - Right Side for the 7.0L engine
* Refer to Programming and Relearning.Programming and Relearning