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HOMESERVICE MANUALSCHEVROLET2000CAB & CHASSIS C2500, 5.7 R, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM & COMPONENT TESTSFUEL SYSTEM (CNG)LOCK-OFF RELAY
2000 Chevrolet Cab & Chassis C2500, 5.7 R, Automatic

Lock-Off Relay

2000 Chevrolet Cab & Chassis C2500, 5.7 R, AutomaticSECTION Lock-Off Relay
  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. Turn ignition off. Disconnect 2-pin Low Pressure Lock-Off (LPL) connector C014. Using test light connected to ground, probe LPL harness connector terminal "A" (Purple wire). Start engine. If test light illuminates, go to next step. If test light does not illuminate, go to step  6.
  3. Turn ignition off for 30 seconds. Turn ignition on. Using scan tool, clear AF ECU DTCs. Connect test light between LPL harness connector terminals "A" and "B". Monitor test light while cranking engine. If test light illuminates, go to next step. If test light does not illuminate, go to step  10.
  4. Turn ignition off. Remove fuel tank cover. Disconnect 2-pin High Pressure Lock-Off (HPL) connector C313. Using test light connected to ground, probe HPL harness connector terminal "A" (Purple wire). Start engine. If test light illuminates, go to next step. If test light does not illuminate, go to step  11.
  5. Turn ignition off for 30 seconds. Turn ignition on. Using scan tool, clear AF ECU DTCs. Connect test light between HPL harness connector terminals "A" and "B". Monitor test light while turning ignition on. If test light flashes, go to step  18. If test light does not flash, go to step  10.
  6. Ensure engine is running. Using test light connected to ground, probe lock-off relay terminal No. 87 (Purple wire). If test light does not illuminate, go to next step. If test light illuminates, go to step  12.
  7. Turn ignition off. Remove lock-off relay. Start engine. Connect test light between relay connector terminals No. 85 (Gray wire) and No 86 (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step  9.
  8. Ensure engine is running. Connect test light between relay connector terminal No. 30 (Orange wire) and ground. If test light illuminates, go to step  16. If test light does not illuminate, go to step  13.
  9. Ensure engine is running. Connect test light between relay connector terminal No. 85 (Gray wire) and ground. If test light illuminates, go to step  14. If test light does not illuminate, go to step  15.
  10. Check for poor contact or open circuit on Purple wire between relay and LPL or HPL. If no problem is found, go to step  17. If any problem is found, repair as necessary. After repairs, go to step  18.
  11. Repair open Purple wire between HPL terminal "A" and splice. See WIRING DIAGRAMS article. After repairs, go to step  18.
  12. Repair open Purple wire between LPL terminal "A" and splice. See WIRING DIAGRAMS article. After repairs, go to step  18.
  13. Repair open Orange wire between relay terminal No. 30 and splice. See WIRING DIAGRAMS article. After repairs, go to step  18.
  14. Repair open Black wire between relay terminal No. 86 and ground. After repairs, go to step  18.
  15. Repair open Gray wire between relay terminal No. 85 and splice. See WIRING DIAGRAMS article. After repairs, go to step  18.
  16. Replace lock-off relay. After repairs, go to step  18.
  17. Replace AF ECU. Program AF ECU. After repairs, go to next step.
  18. 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.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.