GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 XLR 🢒 Vehicle Control Systems 🢒 Vehicle DTC 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 in Wiring Systems.
    • Refer to Fuel Level Specifications in order to verify the correct fuel level sensor readings. The Fuel Tank Level Remaining (%) parameter is available on the scan tool in the engine control module (ECM) Enhanced evaporative emission (EVAP) data list.

Important: When inspecting for a deformed or warped fuel tank, measure the resistance of the suspect fuel level sensor at empty, with the sensor in the fuel tank, and again with the sensor removed from the fuel tank. The measured resistance values should be the same at empty. If the measured resistance values are not the same, refer to Fuel Tank Replacement - Left Side or to Fuel Tank Replacement - Right Side in Engine Controls.

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 be set in the ECM when you perform this diagnostic table.

Step

Action

Value(s)

Yes

No

Schematic Reference: Instrument Cluster Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Turn ON the ignition, 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 16

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 male terminal side.
  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 from 40-250 ohms.
  5. With the scan tool, observe the Fuel Level Sensor Right Volts parameter in engine control module (ECM) evaporative emission (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?

0.7-2.5 V

Go to Step 4

Go to Step 10

4

  1. Connect the J 33431-C Signal Generator and Instrument Panel Tester 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 ON the ignition, 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 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?

0.7-2.5 V

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 and Connector Repairs in Wiring Systems.
    • 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 sender
    • A deformed fuel tank

Did you find and correct the condition?

--

Go to Step 18

Go to Step 6

6
  1. Remove the primary fuel level sender.
  2. Inspect for the following items:
    3. • A stuck fuel level sensor--For example, the fuel strainer interfering with the sender 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 sender.
  2. Inspect for the following items:
    3. • A stuck fuel level sensor--For example, the fuel strainer interfering with the sender 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 in Wiring Systems.

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 in Wiring Systems.

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 sensors for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

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 ECM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

14

Replace the primary fuel level sensor. Refer to Fuel Level Sensor Replacement - Left Side in Engine Controls.

Did you complete the replacement?

--

Go to Step 18

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15

Replace the secondary fuel level sensor. Refer to Fuel Level Sensor Replacement - Right Side in Engine Controls.

Did you complete the replacement?

--

Go to Step 18

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16

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

Did you complete the replacement?

--

Go to Step 18

--

17

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems 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 ECM DTCs.
  2. Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 2