GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2009 🢒 SLS 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Fuel Gage Inaccurate or Inoperative

Diagnostic Aids
    • Ensure 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.
    • Refer to Fuel Level Specifications in order to verify the correct fuel level sensor readings. The Fuel Level Sensor Left and the Fuel Level Sensor Right parameters are available on the scan tool in the ECM EVAP Data list.
    • There is a wire color change before and after C420.

Test Description

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

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

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

Step

Action

Value(s)

Yes

No

Schematic Reference: Instrument Cluster Schematics

Connector End View Reference: Component Connector End Views or Inline Harness Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Turn the ignition ON, with the engine OFF.
  2. Install a scan tool.
  3. With the scan tool, perform the Displays Test in the instrument panel cluster (IPC) Special Functions Output Controls list.

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

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Go to Step 3

Go to Step 6

3

  1. Disconnect C420, 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 Signal Primary and the low reference circuit of the fuel level sensors on the female terminal side.
  3. Turn the ignition ON, with the engine OFF.

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

  4. Vary the resistance on the J 33431-C from 40-250 ohms.
  5. With the scan tool, observe the Fuel Level Sensor Right Volts parameter in ECM EVAP Data list.
  6. Refer to Fuel Level Specifications in order to convert from resistance to Fuel Level Sensor Right Volts.

Does the Fuel Level Sensor Right Volts parameter change smoothly across the specified range?

0.7-2.5V

Go to Step 4

Go to Step 10

4

  1. Connect the J 33431-C between the signal circuit of the Fuel Level Sensor Signal Secondary and the low reference circuit of the fuel level sensors on the male terminal side.
  2. Turn the ignition ON, with the engine OFF.

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

  3. Vary the resistance on the J 33431-C from 40-250 ohms.
  4. With the scan tool, observe the Fuel Level Sensor Left Volts parameter in ECM EVAP Data list.
  5. Refer to Fuel Level Specifications in order to convert from resistance to Fuel Level Sensor Left Volts.

Does the Fuel Level Sensor Left Volts parameter change smoothly across the specified range?

0.7-2.5V

Go to Step 5

Go to Step 11

5

Inspect for the following items:

    • A poor connection at the harness connector of the suspect fuel level sensor - Refer to Testing for Intermittent Conditions and Poor Connections.
    • A high resistance in the fuel level sensor signal primary signal circuit or the low reference circuit between the fuel level sensors and C420
    • A high resistance in the fuel level sensor signal secondary signal circuit or the low reference circuit between the fuel level sensors and C420
    • A misaligned fuel level sensor
    • A deformed fuel tank

Did you find and correct the condition?

--

Go to Step 8

Go to Step 6

6
  1. Remove the primary fuel level sensor.
  2. Inspect for the following items:
    3. • A stuck fuel level sensor
    • For example: the fuel strainer interfering with the sensor float arm.
    • Foreign material in the fuel tank, i.e. ice

Did you find and correct the condition?

--

Go to Step 18

Go to Step 7

7
  1. With the DMM, measure the resistance of the primary 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 Ohms

Go to Step 8

Go to Step 14

8
  1. Remove the secondary fuel level sensor.
  2. Inspect for the following items:
    3. • A stuck fuel level sensor
    • For example: The fuel strainer interfering with the sensor float arm.
    • Foreign material in the fuel tank, i.e. ice

Did you find and correct the condition?

--

Go to Step 18

Go to Step 9

9
  1. With the DMM, measure the resistance of the secondary 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 Ohms

Go to Diagnostic Aids

Go to Step 15

10

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

Did you find and correct the condition?

--

Go to Step 18

Go to Step 12

11

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

Did you find and correct the condition?

--

Go to Step 18

Go to Step 13

12

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

Did you find and correct the condition?

--

Go to Step 18

Go to Step 13

13

Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

14

Replace the primary fuel level sensor. Refer to Primary Fuel Level Sensor Replacement for the 2.8L, 3.0L, 3.2L or 3.6L engines or Primary Fuel Level Sensor Replacement for the 4.6L engine.

Did you complete the replacement?

--

Go to Step 18

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15

Replace the secondary fuel level sensor. Refer to Secondary Fuel Tank Module Replacement for the 2.8L, 3.0L 3.2L or 3.6L engines or Secondary Fuel Tank Module Replacement for the 4.6L engine.

Did you complete the replacement?

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Go to Step 18

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16

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

Did you complete the replacement?

--

Go to Step 18

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17

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 18

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18
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2