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Home >> GMC >> 2001 >> C3500 HD 8.1 G, Standard >> Repair and Diagnosis >> Accessories & Equipment >> Gauges & Instrument Panels >> Instrument Panel System Displays, Gauges And Console >> Diagnostic Information and Procedures >> Fuel Gauge Inaccurate or Inoperative (Dual Tanks) >> Test Description

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. 3 

    This step tests for high resistance in the signal circuits and the low reference circuit of the fuel level senders.

  2. 13 

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

Fuel Gauge Inaccurate or Inoperative (Dual Tanks)

Step Action Value(s) Yes No
Schematic Reference:  Instrument Cluster Schematics  
1 Did you perform the Instrument Cluster Diagnostic System Check? - Go to Step 2  Go to Diagnostic System Check - Instrument Cluster 
2
  1. Disconnect C152.
  2. Connect a jumper wire between the signal circuit of the primary fuel level sender and the signal circuit of the secondary fuel level sender (male terminal side).
  3. Connect the J 33431-C  Signal Generator and Instrument Panel Tester between the signal circuits of the fuel level senders and the low reference circuit of the fuel level senders (male terminal side).
  4. Turn ON the ignition, with the engine OFF.
  5. Vary the resistance on the J 33431-C  from 40-250 Ω.
    IMPORTANT:

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

  6. Refer to Fuel Level Specifications  in order to convert from resistance to fuel gauge display.
Does the fuel gauge display the correct fuel level?		 - Go to Step 4  Go to Step 3 
3 
  1. Install the scan tool.
  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 Ω.
  4. Refer to Fuel Level Specifications  in order to convert from resistance to fuel level %.
    5. IMPORTANT:

    Turn OFF the ignition 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:
    • Fuel Tank Level Remaining % parameter in the PCM Enhanced Evap Data list (gas only)
    • Fuel Level Sensor % parameter in Engine Data Fuel System display (6.6 L diesel only)
Does the scan tool display the correct fuel level %?		 - Go to Step 11  Go to Step 5 
4 Inspect for the following items:
  • A poor connection at the harness connectors of the fuel level senders

    Refer to Testing for Intermittent Conditions and Poor Connections , and Connector Repairs in Wiring Systems.

  • A high resistance in the signal circuits or the low reference circuit between the fuel level senders and C152
  • 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 13  Go to Step 7 
5 Test the signal circuits of the fuel level senders for a high resistance between C152 and the PCM. Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 13  Go to Step 6 
6 Test the low reference circuit of the fuel level senders for a high resistance between C152 and the PCM. Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 13  Go to Step 9 
7
  1. Remove the fuel level senders.
  2. Inspect for the following items:
    • A stuck fuel level sender (i.e. the fuel strainer interfering with the sender float arm)
    • Foreign material in the fuel tanks (ice)
Did you find and correct the condition?		 - Go to Step 13  Go to Step 8 
8
  1. With the J 39200 DMM, measure the resistance of the fuel level senders 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 Go to Diagnostic Aids Go to Step 10 
9 Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections , and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 13  Go to Step 12 
10 Replace the primary or the secondary fuel level sender. Refer to:
Did you complete the replacement?		 - Go to Step 13  -
11 Replace the IPC. Refer to Instrument Cluster Replacement .
Did you complete the replacement?		 - Go to Step 13  -
12
IMPORTANT:

Program the replacement PCM.

Replace the PCM. Refer to:Did you complete the replacement?		 - Go to Step 13  -
13 
  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 
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