Fuel Gage Inaccurate or Inoperative

FUEL GAGE INACCURATE OR INOPERATIVE

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
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 misfire and evaporative emission (EVAP) diagnostics.

CIRCUIT/SYSTEM TESTING
1. Disconnect C309.
2. Connect a signal generator and instrument panel tester between the signal circuit of the fuel level sender and the low reference circuit of the fuel sender on the male side.
3. With the ignition ON and the engine OFF, vary the resistance on the signal generator from 40-250 ohms.
- If the fuel gage displays the correct fuel level, check the signal circuit and the low reference circuit of the fuel level sensor for a high resistance between the fuel level sensor and C309.
- If both the signal circuit and the low reference circuit tests normal, check for a poor connection at the harness connector of the fuel level sensor.
- If the harness connector is normal, check for a misaligned fuel sender or a misaligned fuel tank.
4. Install a scan tool.
5. With the ignition ON and the engine OFF, vary the resistance on the signal generator from 40-250 ohms and observe the Fuel Level Remaining parameter in the ECM EVAP Data list.
- If the scan tool does not display the correct fuel level percent, replace the instrument panel cluster (IPC).
- If the scan tool does display the correct fuel level percent, check the signal circuit and the low reference circuit of the fuel level sensor for a high resistance between the ECM and C309.
- If both the signal circuit and the low reference circuit tests normal, check for a poor connection at the harness connector of the ECM.
- If the harness connector is normal, replace the ECM.

COMPONENT TESTING
Measure the resistance of the float arm of the fuel level sender while moving the float arm between 40-250 ohms.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Fuel Level Sensor Replacement
- Control Module References for the ECM and IPC replacement, setup, and programming