GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC Suburban - 2WD 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 Fuel Gage Inaccurate or Inoperative

Diagnostic Aids
    • Verify that the fuel level is in the same range as the customer concern.
    • Use the fuel level sensor resistance in order to verify the fuel level sensor operation. When the fuel tank is empty, the fuel level sensor resistance is approximately 40 ohms. When the fuel tank is full the fuel level sensor resistance is approximately 250 ohms.

Test Description

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

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

Step

Action

Value(s)

Yes

No

1

Did you perform the Instrument Cluster Diagnostic System Check?

--

Go to Step 2

Go to Instrument Cluster System Check

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 a jumper wire between the ground circuit of the primary fuel level sensor and ground circuit of the secondary fuel level sensor.
  4. Connect the J 33431-C Signal Generator and Instrument Panel Tester between the signal circuits of the fuel level sensors and the ground circuits of the fuel level sensors.
  5. Turn the ignition ON, with the engine OFF.

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

  6. Vary the resistance on the J 33431-C from 40-250 ohms.
  7. Observe the fuel gage in the IPC.

Does the fuel gage move from empty to full?

--

Go to Step 4

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect C2 at the fuel tank pump balance module.
  3. Connect the J 33431-C Signal Generator and Instrument Panel Tester between the fuel level signal circuit of the vehicle control module (VCM) and the 5 volt reference circuit.
  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 from 40-250 ohms.

Does the fuel gage move off of empty?

--

Go to Step 6

Go to Step 5

4

Inspect for the following items:

    • A poor connection at the harness connectors of the primary and the secondary fuel level sensors.
    • A misaligned primary or secondary fuel level sender.
    • A deformed primary or secondary fuel tank.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 8

5
  1. Turn the ignition OFF.
  2. Disconnect C1 at the VCM.
  3. Turn the ignition ON, with the engine OFF.
  4. Connect the J 33431-C Signal Generator and Instrument Panel Tester between the fuel level signal circuit of the IPC and a good ground.

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

  5. Vary the resistance on the J 33431-C from 0-90 ohms.

Does the fuel gage move from empty to full?

--

Go to Step 10

Go to Step 14

6

Test the signal circuits of the primary and the secondary fuel level sensors for an open, for a short to ground, or for a high resistance.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 7

7

Test the ground circuits of the primary and the secondary fuel level sensors for an open or for a high resistance.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 11

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

Did you find and correct the condition?

--

Go to Step 22

Go to Step 9

9
  1. With the J 39200 DMM, measure the resistance of the primary and the secondary fuel level sensors while moving the float arm.
  2. Observe both the analog and the digital displays on the DMM.

Does the resistance for both fuel level sensors change smoothly across the specified range?

40-250 ohms

Go to Diagnostic Aids

Go to Step 18

10

Test the 5 volt reference circuit for an open, for a short to ground, or for a high resistance.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 13

11

Test the ground circuit of the fuel tank pump balance module for an open or for a high resistance.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 12

12

Test the Ignition 1 circuit for an open, a short to ground, or for a high resistance.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 16

13

Test the fuel level signal circuit for an open, for a short to ground, or for a high resistance between the fuel tank pump balance module and the VCM.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 17

14

Test the fuel level signal circuit of the IPC for an open, for a short to ground, or for a high resistance between the VCM and the IPC.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 15

15

Inspect for poor connections at the harness connector of the IPC.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 19

16

Inspect for poor connections at the harness connector of the fuel tank pump balance module.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 20

17

Inspect for poor connections at the harness of the VCM.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 21

18

Replace the fuel level sensor that did not have the correct resistance values. Refer to the appropriate procedure:

    •  Fuel Level Sensor Replacement in Engine Controls- 5.0 L and 5.7 L.
    •  Fuel Level Sensor Replacement in Engine Controls - 7.4 L.

Did you complete the replacement?

--

Go to Step 22

--

19

Replace the IPC. Refer to Instrument Cluster Replacement .

Did you complete the replacement?

--

Go to Step 22

--

20

Replace the fuel tank pump balance module.

Did you complete the replacement?

--

Go to Step 22

--

21

Important:: Program the replacement VCM.

Replace the VCM. Refer to the appropriate procedure:

    •  VCM Replacement/Programming in Engine Controls- 5.0 L and 5.7 L.
    •  VCM Replacement/Programming in Engine Controls - 7.4 L..

Did you complete the replacement?

--

Go to Step 22

--

22

  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