Fuel Gage Inaccurate or Inoperative (Single Tank)

FUEL GAGE INACCURATE OR INOPERATIVE (SINGLE TANK)

DIAGNOSTIC FAULT INFORMATION
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview

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 high speed GMLAN serial data to the body control module (BCM). The BCM then sends the fuel information to the instrument panel cluster (IPC) via low speed GMLAN in order to display the fuel gage. The fuel information is also used for misfire and evaporative emission (EVAP) diagnostics.

CIRCUIT/SYSTEM TESTING
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 40-250 ohms. Verify that the scan tool Fuel Tank Level Remaining parameter displays the correct fuel level percent.
- If the fuel level percent is incorrect, test the signal circuit and the low reference circuit for an open/high resistance. If the circuits test normal, replace the ECM.
3. Ignition ON, vary the resistance on the signal generator from 40-250 ohms and monitor the fuel gage.
- If the gage is incorrect, replace the IPC.
4. If all circuits test normal, test or replace the fuel level sensor.

REPAIR INSTRUCTIONS
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Fuel Level Sensor Replacement (1500 Series) Fuel Level Sensor Replacement (1500 Series w/E85) Fuel Level Sensor Replacement (2500 - 43.5L (11.5 gal) Tank - Rear) Fuel Level Sensor Replacement (2500 - 98.4L (26 gal) Tank - Front) for the 4.8L, 5.3L, 6.0L, and 6.2L engines
- Control Module References for ECM and IPC replacement, setup, and programming. Programming and Relearning Verification Tests