Fuel Gage Inaccurate or Inoperative (Dual Tanks)

Fuel Gage Inaccurate or Inoperative (Dual Tank)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

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 Verification

Ignition ON, verify DTC P0461, P0462, P0463, P0464, P2066, P2067, or P2068 is not set

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle. Diagnostic Trouble Code Descriptions

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the primary and secondary fuel level sensors.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the primary fuel level sensor low reference circuit terminal B and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition OFF, test for less than 1.0 ohm of resistance between the secondary fuel level sensor low reference circuit terminal B and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

4. Jumper the primary fuel level sensor signal circuit terminal C to secondary fuel level sensor signal circuit terminal C. Install a Signal Generator and Instrument Panel Tester between the jumped signal circuits and ground.
5. Ignition ON, vary the signal generator resistance between 40-250 ohms. Verify that the scan tool Fuel Tank Level Remaining parameter displays a range that varies between 5 and 95 percent as the signal generator resistance changes.

• If not displaying the specified range, test both signal circuits for an open/high resistance. If the circuits test normal, replace the ECM.

6. Vary the signal generator resistance between 40-250 ohms. Verify that the fuel gage displays a range that varies between empty and full as the signal generator resistance changes.

• If not displaying the specified range, replace the IPC.

7. If all circuits test normal, perform the fuel level sensor component test before replacing either the primary or secondary fuel level sensor.

Component Testing

1. Ignition OFF, disconnect the harness connectors at the primary and secondary fuel level sensors.
2. While sweeping the primary fuel level sensor through its full range of motion, test for a minimum value less than 41 ohms and a maximum value greater than 119 ohms of resistance between the signal terminal C and the low reference terminal B.

• If not within the specified range, replace the primary fuel level sensor.

3. While sweeping the secondary fuel level sensor through its full range of motion, test for a minimum value less than 41 ohms and a maximum value greater than 119 ohms of resistance between the signal terminal C and the low reference terminal B.

• If not within the specified range, replace the secondary fuel level sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Fuel Level Sensor Replacement for the 6.0L (LFA) engine
* Fuel Level Sensor Replacement (1500 Series) Fuel Level Sensor Replacement (1500 Series w/E85) Fuel Level Sensor Replacement (2500 - 98.4L (26 gal) Tank - Front) Fuel Level Sensor Replacement (2500 - 43.5L (11.5 gal) Tank - Rear) for the 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L engine