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Fuel Gauge Relay

NOTE: To perform this test, vehicle must be operating on CNG.
  1. Perform OBD system check. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. Go to next step.
  2. Using scan tool, command AF ECU fuel gauge output from full to empty. If gauge responds properly, go to next step. If gauge does not respond properly, go to step  6.
  3. Using scan tool, monitor VCM fuel level data. Depress and release fuel gauge select switch. Compare scan tool gasoline fuel level data to instrument cluster gauge. Gauge should display gasoline level, then return to CNG level display. If gauge is operating properly, go to next step. If gauge does not display properly, go to step  10.
  4. If CNG level is accurate, go to next step. If CNG level is inaccurate, diagnose CNG reading. See CNG FUEL GAUGE READING INACCURATE .
  5. If gasoline level is accurate, test is complete. If gasoline level is inaccurate, diagnose gauge. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
  6. Disconnect fuel gauge relay. Turn ignition on. Connect test light between relay connector terminals No. 85 (Black wire) and No. 86 (Gray wire). If test light illuminates, go to next step. If test light does not illuminate, go to step  12.
  7. Remove test light. Note gauge position. If gauge indicates past full, go to next step. If gauge does not indicate past full, go to step  13.
  8. Using a fused jumper wire, connect relay connector terminal No. 30 (Purple wire) to ground. If gauge moves to empty, go to next step. If gauge does not move to empty, go to step  14.
  9. Remove jumper wire from ground. Connect jumper wire between relay connector terminals No. 30 and No. 87 (Tan/White wire). Using scan tool, command AF ECU fuel gauge output from full to empty. If gauge does not indicate as commanded, go to step  15. If gauge indicates as commanded, go to step  20.
  10. Remove fuel gauge relay. Connect test light between relay connector terminals No. 85 (Black wire) and No. 86 (Gray wire). If test light illuminates, go to next step. If test light does not illuminate, go to step  16.
  11. Remove test light. Connect jumper wire between relay connector terminals No. 30 (Purple wire) and No. 87 (Tan/White wire). Using scan tool, check VCM fuel level data. If gauge and scan tool do not match, go to step  17. If gauge and scan tool match, go to step  20.
  12. Connect test light between relay connector terminal No. 85 (Black wire) and battery voltage. If test light illuminates, go to step  18. If test light does not illuminate, go to step  19.
  13. Check Purple wire for short to ground or short to power (if jumper fuse blows). Repair as necessary. If no problem is found, repair instrument cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step  22.
  14. Check Purple wire for open circuit or poor contact. Repair as necessary. If no problem is found, repair instrument cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step  22.
  15. Check Tan/White wire for open, poor contact, short to power or short to ground. If no problem is found, go to step  21. If problem is found, repair as necessary. After repairs, go to step  22.
  16. Check for short to power on Gray wire. If no problem is found, go to step  21. If problem is found, repair as necessary. After repairs, go to step  22.
  17. Repair open, poor contact, short to power or short to ground on Purple/White wire between fuel gauge relay terminal No. 87A and connector C019 terminal "C" and Purple wire between connector C019 terminal "C" and VCM connector C1 terminal No. 9. After repairs, go to step  22.
  18. Check for open or short to ground on Gray wire. If no problem is found, go to step  21. If problem is found, repair as necessary. After repairs, go to step  22.
  19. Repair open on Black wire between fuel gauge relay terminal No. 85 and splice S009. After repairs, go to step  22.
  20. Replace fuel gauge relay. After repairs, go to step  22.
  21. Replace AF ECU and reprogram. After repairs, go to next step.
  22. Reconnect all components and connectors. Using scan tool, clear all DTCs. Turn ignition off for 30 seconds. Start engine. Test drive vehicle. If no problems are found, MIL operates properly and no DTCs are set, test is complete. If any problems are found, MIL does not operate properly or DTCs are set, perform OBD system check. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
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