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

High Resistance

Open

Short to Voltage

Signal Performance

Fuel Level Sensor 1 Signal Circuit

P0462

1

P0463

P0464

P0463

P0461

Fuel Level Sensor 2 Signal Circuit

P2067

1

P2068

P2068

P2066 or P2636

Fuel Level Sensor Low Reference Circuit

--

1

P0463

P2068

P0464

P0463

P2068

P0461

P2066 or P2636

1. Fuel Gage Inaccurate or Inoperative.

Circuit/System Description

The fuel level sender changes resistance in response to the fuel level. The engine control module (ECM) monitors the signal circuit 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 primary and the secondary fuel level sender resistance is low and the ECM senses a low signal voltage. When the fuel tank is empty, the primary and the secondary fuel level sender resistance is high and the ECM senses a high signal voltage. The ECM uses the signal circuit of the primary and secondary fuel level sender in order to calculate the percentage of remaining fuel in the tanks. The ECM sends the fuel level information via the serial data circuit to the instrument panel cluster (IPC) for display in the fuel gage.

Reference Information

Schematic Reference

Instrument Cluster Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Instrument Cluster Description and Operation

Electrical Information Reference

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

Scan Tool Reference

Control Module References for scan tool information.

Special Tools

J 33431-C Instrument Panel Tester

Circuit/System Verification

Ignition ON, observe the scan tool Fuel Tank Level Remaining parameter. The reading should be between 4-98 percent.

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 between the primary fuel level sensor low reference circuit terminal 4 and ground.
  3. 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. Ignition OFF, test for less than 1 ohm between the secondary fuel level sensor low reference circuit terminal 4 and ground.
  5. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  6. Jumper the primary fuel level sensor signal circuit terminal 1 to the secondary fuel level sensor signal circuit terminal 1. 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 terminal 1 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, remove primary and secondary fuel level senders.
  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 between signal terminal 1 and the low reference terminal 4.
  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 between signal terminal 1 and the low reference terminal 4.
  5. If not within the specified range, replace the secondary fuel level sensor.

Repair Instructions

Perform the Diagnostic Repair Verification

    •  Fuel Level Sensor Replacement - Left Side for the 4.6L engine
    •  Fuel Level Sensor Replacement - Right Side for the 4.6L engine
    •  Fuel Level Sensor Replacement - Left Side for the 4.4L engine
    •  Fuel Level Sensor Replacement - Right Side for the 4.4L engine
    •  Control Module References for the ECM or IPC replacement, setup, and programming