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Home >> GMC >> 1999 >> Forward Control 6.5 Y, Automatic >> Repair and Diagnosis >> Accessories & Equipment >> Gauges & Instrument Panels >> Instrument Panel - Analog - P Series >> System Tests >> Fuel Gauge Is Inaccurate (Gasoline)

Fuel Gauge Is Inaccurate (Gasoline)

  1. Ensure ignition is off. Disconnect VCM connector C1. Connect signal generator J33431B between VCM connector C1 terminal No. 9 (Purple wire) and ground. Turn ignition on. Turn signal generator control slowly from zero ohms to 90 ohms. If gauge reading does not vary from empty to full, go to next step. If gauge reading varies from empty to full, go to step  3.
  2. Replace instrument panel cluster. Recheck system.
  3. Turn ignition off. Disconnect VCM connector C3. Check resistance between connector C3 terminals No. 13 (Purple wire) and No. 19 (Black wire). If resistance is not 40-250 ohms, go to next step. If resistance is 40-250 ohms, go to step  7.
  4. Disconnect fuel pump module. Check resistance between fuel pump module connector cavities "A" and "D". If resistance is 40-250 ohms, go to next step. If resistance is not 40-250 ohms, go to step  6.
  5. Change the amount of fuel in fuel tank by adding or removing fuel. Check resistance between fuel pump module connector cavities "A" and "D". If resistance changed in relation to amount of change in fuel level, system is okay. If resistance did not change in relation to amount of change in fuel level, go to next step.
  6. Replace fuel pump module. Recheck system.
  7. Change the amount of fuel in fuel tank by adding or removing fuel. Check resistance between VCM connector C3 terminals No. 13 and No. 19. If resistance changed in relation to amount of change in fuel level, go to step  10. If resistance did not change in relation to amount of change in fuel level, go to step  6.
  8. Check for open or short to ground on Purple wire between VCM connector C3 terminal No. 13 and fuel pump module connector terminal "A" and Black wire between VCM connector C3 terminal No. 19 and fuel pump module connector terminal "D". If an open or short exists, go to next step. If no problem is found, go to step  10.
  9. Repair open on Purple wire between VCM connector C3 terminal No. 13 and fuel pump module connector terminal "A" or Black wire between VCM connector C3 terminal No. 19 and fuel pump module connector terminal "D". Recheck system.
  10. Replace VCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE.
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