GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

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

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Fuel Level Sensor Reference Voltage Circuit

P0462

P2067

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--

P0461

P2066

Fuel Level Sensor 1 Signal Circuit

Fuel Level Sensor 2 Signal Circuit

P0462

P2067

P0463

P2068

P0463

P2068

P0461

P2066

Fuel Level Sensor Low Reference Circuit

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P0463

P2068

P0463

P2068

P0461

P2066

Circuit/System Description

The primary fuel level sender and the secondary fuel level sender changes resistance based on fuel level. The engine control module (ECM) monitors the signal circuits of the primary fuel level sender and the secondary fuel level sender in order to determine the fuel level. When the fuel tank is full, the resistances of both fuel level senders are high and the ECM senses a high signal voltage on both the signal circuits of the primary fuel level sender and the secondary fuel level sender. When the fuel tanks are empty, the resistances of the fuel level senders are low and the ECM senses a low signal voltage. The ECM uses the signal circuits of the primary fuel level sender and the secondary fuel level sender in order to calculate the percentage of remaining fuel in the tank. The ECM sends the fuel level percentage via serial data circuit to the instrument cluster in order to control the fuel gage.

Diagnostic Aids

A partially filled fuel tank and filling the fuel tank with the ignition ON or engine RUNNING may cause an inaccurate or erratic fuel gage. This condition may cause a fuel system DTC to set and the fuel gage to default to empty. Refer to Fuel Gage Description and Operation.

Reference Information

Schematic Reference

    •  Instrument Cluster Schematics
    •  Engine Control Module Connector End Views for the 6.0L engine
    •  Engine Controls Schematics for the 3.6L engine
    •  Engine Controls Schematics for the 2.8L engine

Connector End View Reference

    •  Displays and Gages Connector End Views
    •  Engine Controls Schematics for the 6.0L engine
    •  Engine Control Module Connector End Views for the 3.6L engine
    •  Engine Control Module Connector End Views for the 2.8L engine

Description and Operation

Fuel Gage Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions

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 ohm of resistance between the primary fuel level sensor low reference circuit terminal D and ground.
  3. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuits tests normal, replace the ECM.
  4. Ignition OFF, test for less than 1 ohm of resistance between the secondary fuel level sensor low reference circuit terminal D and ground.
  5. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuits tests normal, replace the ECM.
  6. Jumper the primary fuel level sensor signal circuit terminal A to the secondary fuel level sensor signal circuit terminal A. Install a Signal Generator and Instrument Panel Tester between the jumped signal circuits and the low reference circuit.
  7. Ignition ON, vary the signal generator resistance between 40 and 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.
  8. If not displaying the specified range, test both signal circuits for an open/high resistance. If the circuits test normal, replace the ECM.
  9. Vary the signal generator resistance between 40 and 250 ohms. Verify that the fuel gage displays a range that varies between empty and full as the signal generator resistance changes.
  10. If the gage is incorrect, replace the IPC.
  11. 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 connector 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 signal terminal A and the low reference terminal D.
  3. If not within the specified range, replace the primary fuel level sensor.
  4. 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 signal terminal A and the low reference terminal D.
  5. If not within the specified range, replace the secondary fuel level sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Primary Fuel Level Sensor Replacement for the 6.0L engine
    •  Primary Fuel Level Sensor Replacement for the 3.6L engine
    •  Primary Fuel Level Sensor Replacement for the 2.8L engine
    •  Secondary Fuel Tank Module Replacement for the 6.0L engine
    •  Secondary Fuel Tank Module Replacement for the 3.6L engine
    •  Secondary Fuel Tank Module Replacement for the 2.8L engine
    •  Control Module References for ECM and IPC replacement, setup, and programming