Test C: Fuel Gauge Inoperative Or Inaccurate

1. Perform instrument cluster diagnostic system check. See INSTRUMENT CLUSTER DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. Go to next step.
NOTE: Always verify resistance settings of Signal Generator and Instrument Panel Tester (J33431-C) using a DVOM, before connecting to vehicle.
2. Disconnect in-line harness connector C-305 located under vehicle below rear passenger seat area. Disconnect fuel level sender connector. See Fig 2 . Using Signal Generator and Instrument Panel Tester (J33431-C), connect test leads to fuel level sender input (Purple wire) and fuel sender return (Dark Green wire) terminals on wiring harness side of fuel level sender connector. Turn ignition switch to ON position. Set tester resistance dial to 40 ohms, fuel gauge indicator should read "E". Set tester resistance dial to 250 ohms, fuel gauge indicator should read "F". If fuel gauge readings are not as specified, go to next step. If fuel gauge readings are as specified, go to step  4 .
3. Connect scan tool to Data Link Connector (DLC). While observing PCM EVAP data list, vary resistance between 40 and 250 ohms resistance. Check scan tool display for correct percentage of fuel on fuel gauge. See FUEL LEVEL SPECIFICATIONS  table. If scan tool indicates the correct fuel level percentages for resistance settings, go to step  11 . If scan tool does not display correct fuel level percentages for resistance settings, go to step  5 .
   FUEL LEVEL SPECIFICATIONS
   
   

   Ohms (Fuel Level %)		Fuel Gauge Level
   20 Gallon Tank (Regular Wheel Base)
   215-250 (90-100)		Full
   175 (70)		3/4
   143 (51)		1/2
   106 (30)		1/4
   40-56 (0-7)		Empty
   76 (15)		LOW FUEL Indicator On
   25 Gallon Tank (Long Wheel Base)
   218-250 (90-100)		Full
   171 (70)		3/4
   134 (51)		1/2
   97 (30)		1/4
   40-53 (2-11)		Empty
   54 (12)		LOW FUEL Indicator On

4. Check for an intermittent condition, poor electrical connection or faulty wiring at harness connector for fuel sending unit. Check for an open or high resistance in Purple wire and Black wire between in-line connector C305 and fuel sending unit connector. See Fig 2 . Check for damaged or deformed fuel tank. Repair or replace any faulty condition as necessary and go to step  13 . If no fault was found, go to step  7 .
5. Disconnect PCM connector C2. Measure resistance of Purple wire between PCM connector C2 terminal No. 69 and in-line harness connector C305 terminal 3D. See Fig 1 and Fig 2 . If resistance is 5 ohms or less, go to next step. If resistance is 5 ohms or more, locate and repair open or high resistance in Purple wire. Go to step  13 .
6. Measure resistance of Black wire between PCM connector C2 terminal No. 35 and in-line harness connector C305 terminal 3B. If resistance is 5 ohms or less, go to next step. If resistance is 5 ohms or more, locate and repair open or high resistance in Black wire. Go to step  13 .
7. Remove fuel level sender from fuel tank. Check for misaligned fuel sender, a stuck fuel sender or strainer interference with float arm, or foreign material in gas tank. Repair or replace any faulty condition as necessary and go to step  13 . If fuel sender and float arm are okay, go to next step.
8. Using a DVOM, measure resistance of fuel sender while moving float arm through full range of travel. See FUEL LEVEL SPECIFICATIONS  table. If resistance changes smoothly from 40 ohms through 250 ohms, go to next step. If resistance does not change smoothly, or is not between 40 and 250 ohms, go to step  10 .
9. Inspect for poor connections or poor terminal contact in connectors of PCM. Repair connections as necessary. If PCM connectors are okay, go to step  12 .
10. Replace fuel level sending unit. Go to step  13 .
11. Replace instrument cluster. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. Contact an authorized A/C Delco service center for transfer of information from failed Instrument Panel Cluster (IPC) or affix appropriate label with necessary vehicle information on driver door pillar. Go to step  13 .
12. Replace PCM. Perform appropriate reprogramming procedures for replacement PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION - TRUCKS article in ENGINE PERFORMANCE.
13. Turn ignition switch to OFF position. Restore any previously disconnected components or connectors. Turn ignition switch to ON position. Using scan tool, clear DTCs from PCM. Operate system to verify repair is complete. If fault remains, go to step  2 .

Fig 1: Identifying PCM Connectors C1 & C2 Terminals

Courtesy of GENERAL MOTORS CORP.

Fig 2: Identifying In-Line Connector C305 Terminals

Courtesy of GENERAL MOTORS CORP.