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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series Commercial (Cutaway) C4/C5 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Fuel Gage Inaccurate or Inoperative

Fuel Gage Inaccurate or Inoperative Single Tank

Diagnostic Aids
    • Verify that the fuel level is in the same range as the customer concern.
    • For intermittent diagnosis, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • Refer to Fuel Level Specifications in order to verify the correct readings for the fuel level sensor. The Fuel Level Sensor Voltage parameter is available on the scan tool in the powertrain control module (PCM) Engine Data 1 data list - L18 only. The fuel level sensor % parameter is available on the scan tool in the Fuel Data data list - LLY and LG4 only.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for a high resistance in the signal circuit and the low reference circuit of the fuel level sensor.

    2.

  2. DTCs will set in the PCM when you perform this diagnostic table.

Step

Action

Values

Yes

No

Schematic Reference: Instrument Cluster Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Disconnect the fuel level sensor.
  2. Connect the J 33431-C Signal Generator and Instrument Panel Tester between the signal circuit of the fuel level sensor and the low reference circuit of the fuel level sensor on the female terminal side of the connector.
  3. Turn the ignition ON, with the engine OFF.

    4. Important: Verify the J 33431-C resistance settings with a DMM.

  4. Vary the resistance on the J 33431-C .
  5. Refer to Fuel Level Specifications in order to convert from resistance to fuel gage display.

Does the fuel gage display the correct fuel level?

--

Go to Step 5

Go to Step 3

3

  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.

    3. Important: Verify the J 33431-C resistance settings with a DMM.

  3. Vary the resistance on the J 33431-C .
  4. Refer to Fuel Level Specifications in order to convert from resistance to fuel level percentage.

    5. Important: Turn the ignition OFF momentarily between the resistance settings in order to quickly update the scan tool display.

  5. With the scan tool, observe one of the following fuel level parameters:
    6. • Fuel Level Sensor parameter in the powertrain control module (PCM) Engine Data 1 data list - L18 only
    • Fuel Level Sensor % parameter in the engine control module (ECM) Fuel Data data list - LLY and LG4 only

Does the scan tool display the correct fuel level percentage?

--

Go to Step 4

Go to Step 6

4

With the scan tool, perform the Displays Test in the instrument panel cluster (IPC) scan tool Output Controls.

Does the gage move from 0 to its maximum value and back to 0 when you perform the Displays Test?

--

Go to Step 5

Go to Step 10

5

Inspect for the following items:

    • A poor connection at the harness connector of the fuel level sensor-- Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.
    • A misaligned fuel level sender
    • A deformed fuel tank

Did you find and correct the condition?

--

Go to Step 15

Go to Step 8

6

Test the signal circuit of the fuel level sensor for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 7

7

Test the low reference circuit of the fuel level sensor for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

8
  1. Remove the fuel level sender.
  2. Inspect for the following items:
    3. • The fuel level sensor is stuck, perhaps due to an interference with the fuel strainer.
    • The fuel tank contains foreign material, for instance, ice.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 9

9
  1. With the DMM, measure the resistance of the fuel level sensor while moving the float arm.
  2. Observe both the analog and digital displays on the DMM.

Does the resistance change smoothly across the specified range?

40-250 Ω (L18 and LLY) or 0-90 Ω (LG4)

Go to Diagnostic Aids

Go to Step 12

10

Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

11

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

12

Replace the fuel level sensor. Refer to one of the following procedures:

    •  Fuel Sender Assembly Replacement for the 6.6L (LLY) engine
    •  Fuel Sender Assembly Replacement for the 7.8L engine
    •  Fuel Sender Assembly Replacement for the 8.1L engine

Did you complete the replacement?

--

Go to Step 15

--

13

Replace the instrument panel cluster (IPC). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 15

--

15

  1. Use the scan tool in order to clear the PCM DTCs.
  2. Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2

Fuel Gage Inaccurate or Inoperative Dual Tank

Diagnostic Aids
    • Verify that the fuel level is in the same range as the customer concern.
    • For intermittent diagnosis, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • Refer to Fuel Level Specifications in order to verify the correct readings for the fuel level sensors. The Fuel Level Sensor Voltage parameter is available on the scan tool in the PCM Engine Data 1 data list - L18 only. The Fuel Level Sensor % parameter is available on the scan tool in the Fuel Data data list - LLY and LG4 only.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for a high resistance in the signal circuits and the low reference circuits of the fuel level sensors.

    2.

  2. DTCs will set in the powertrain control module (PCM) when you perform this diagnostic table.

Step

Action

Value(s)

Yes

No

Schematic Reference: Instrument Cluster Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Disconnect the primary and the secondary fuel level sensors.
  2. Connect a jumper wire between the signal circuit of the primary fuel level sensor and the signal circuit of the secondary fuel level sensor.
  3. Connect the J 33431-C Signal Generator and Instrument Panel Tester between the signal circuit of the fuel level sensors and the low reference circuit of the fuel level sensors on the female terminal side of the connector.
  4. Turn the ignition ON, with the engine OFF.

    5. Important: Verify the J 33431-C resistance settings with a DMM.

  5. Vary the resistance on the J 33431-C .
  6. Refer to Fuel Level Specifications in order to convert from resistance to fuel gage display.

Does the fuel gage display the correct fuel level?

--

Go to Step 5

Go to Step 3

3

  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.

    3. Important: Verify the J 33431-C resistance settings with a DMM.

  3. Vary the resistance on the J 33431-C .
  4. Refer to Fuel Level Specifications in order to convert from resistance to fuel level percentage.

    5. Important: Turn the ignition OFF momentarily between the resistance settings in order to quickly update the scan tool display.

  5. With the scan tool, observe one of the following fuel level parameters:
    6. • Fuel Level Sensor parameter in the powertrain control module (PCM) Engine Data 1 data list - L18
    • Fuel Level Sensor % parameter in the Fuel Data data list - LLY and LG4 only

Does the scan tool display the correct fuel level percentage?

--

Go to Step 4

Go to Step 6

4

With the scan tool, perform the Displays Test in the instrument panel cluster (IPC) scan tool Output Controls.

Does the gage move from 0 to its maximum value and back to 0 when you perform the Displays Test?

--

Go to Step 5

Go to Step 10

5

Inspect for the following items:

    • A poor connection at the harness connector of the fuel level sensors-- Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.
    • A misaligned primary fuel level sender or secondary fuel level sender
    • A deformed primary fuel tank or secondary fuel tank

Did you find and correct the condition?

--

Go to Step 15

Go to Step 8

6

Test the signal circuits of the fuel level sensors for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 7

7

Test the low reference circuits of the fuel level sensors for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

8
  1. Remove the fuel level senders.
  2. Inspect for the following items:
    3. • The fuel level sensors are stuck, perhaps due to an interference with the fuel strainer.
    • The fuel tanks contain foreign material, for instance, ice.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 9

9
  1. With the DMM, measure the resistance of each fuel level sensor while moving the float arm.
  2. Observe both the analog and digital displays on the DMM.

Does the resistance change smoothly across the specified range for each fuel level sensor?

40-250 Ω (L18) or 0-90 Ω (LG4)

Go to Diagnostic Aids

Go to Step 12

10

Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

11

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

12

Replace the fuel level sensor that did not respond correctly to the last inspection. Refer to one of the following procedures:

    •  Fuel Sender Assembly Replacement for the 6.6L (LLY) engine
    •  Fuel Sender Assembly Replacement for the 7.8L engine
    •  Fuel Sender Assembly Replacement for the 8.1L engine

Did you complete the replacement?

--

Go to Step 15

--

13

Replace the instrument panel cluster (IPC). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 15

--

15

  1. Use the scan tool in order to clear the PCM DTCs.
  2. Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2