Fuel Gage Inaccurate or Inoperative (Dual Tanks)

FUEL GAGE INACCURATE OR INOPERATIVE (DUAL TANKS)


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 circuits of the primary and secondary fuel level sensors in order to determine the fuel level. When the fuel tanks are full, the sensor resistances are low and the ECM senses a low signal voltage. When the fuel tanks are empty, the sensor resistances are high and the ECM senses a high signal voltage. The ECM uses the signal circuits of the primary and secondary fuel level sensors in order to calculate the percentage of remaining fuel in the tanks. 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 level information to the instrument panel cluster (IPC) via low speed GMLAN in order to display the fuel level. 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 primary and secondary fuel level sensors. Jumper the 2 signal circuits together and then install a signal generator and instrument panel tester between the signal circuits 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 both signal circuits 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 either the primary or secondary 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