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Home >> Cadillac >> 2002 >> Escalade EXT >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Fuel System (Bi-Fuel & CNG) >> Fuel Lock-Off Relay >> Diagnostic Procedure
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Diagnostic Procedure

  1. Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
  2. Disconnect lock-off solenoid relay connector. Connect Test Light (J 34142-B) between relay switch power supply circuit terminal No. 30 and a known good ground. Does test light illuminate? If yes, go to next step. If no, go to step  6.
  3. Connect Test Light (J 34142-B) between relay coil ground circuit terminal No. 86 and battery positive. Does test light illuminate? If yes, go to next step. If no, go to step  16.
  4. Connect Test Light (J 34142-B) between relay coil power circuit terminal No. 85 and a known good ground. Observe test light as you turn the ignition ON while leaving the engine OFF. Does test light briefly illuminate? If yes, go to next step. If no, go to step  8.
  5. Turn OFF the ignition. Connect lock-off solenoid relay connector. Backprobe lock-off solenoid relay switch output circuit terminal No. 87 with Test Light (J 34142-B) connected to a known good ground. Observe test light as you turn the ignition ON while leaving the engine OFF. Does test light briefly illuminate? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to step  18.
  6. Inspect AFS 20-amp MaxiFuse®. Is fuse open? If yes, go to step  10. If no, go to next step.
  7. Test AFS MaxiFuse® circuit for an open condition between Fuse Block - Underhood connector terminal and lock-off solenoid relay connector terminal. Test underhood fuse block for proper operation. Inspect underhood fuse block connector terminal and lock-off solenoid relay connector terminal for proper contact. Inspect in-line connector terminal "E" for proper terminal contact. Repair wiring or terminal contact as necessary. After repairs, go to step  21.
  8. Turn OFF the ignition. Disconnect in-line connector C006. Connect Test Light (J 34142-B) between PCM harness fuel pump relay Control circuit terminal "E" and a known good ground. Observe test light as you turn ON the ignition leaving the engine OFF. Does test light briefly illuminate? If yes, go to step  15. If no, go to next step.
  9. Test for an open fuel pump relay Control circuit between gasoline PCM and in-line connector C006. Inspect PCM connector and in-line connector C006 for proper terminal contact. Repair wiring or terminals as necessary. Did you find and correct the condition? If yes, go to step  21. If no, go to step  20.
  10. Replace AFS 20-amp MaxiFuse®. Inspect AFS 20-amp MaxiFuse®. Did replacement fuse open? If yes, go to step  17. If no, go to next step.
  11. Turn the ignition OFF. Disconnect LPL connector. Remove fuel tank cover. Disconnect HPL connector. Connect Test Light (J 34142-B) between lock-off solenoid relay switch output circuit terminal No. 87 and battery positive. Is test light illuminated? If yes, go to step  19. If no, go to next step.
  12. With DMM (J 39200) measure and record resistance between High Pressure Lock-Off (HPL) solenoid connector terminals. Is HPL solenoid outside of 16.3-20.6 ohms? If yes, replace HPL solenoid. If no, go to next step.
  13. With DMM (J 39200) measure and record resistance between Low Pressure Lock-Off (LPL) solenoid connector terminals. Is LPL solenoid outside of 6.2-10 ohms? If yes, replace LPL solenoid. If no, go to next step.
  14. Replace AFS 20-amp MaxiFuse®. Connect HPL solenoid. Crank engine for 10 seconds. Inspect AFS 20-amp MaxiFuse®. Is fuse open? If yes, replace HPL solenoid. If no, replace LPL solenoid.
  15. Test for an open circuit between lock-off relay coil power supply terminal No. 85 and in-line connector terminal "E". Test for a short to ground on lock-off relay coil power supply circuit. Repair wiring as necessary. After repairs, go to step  21.
  16. Repair open lock-off solenoid relay coil ground circuit. After repairs, go to step  21.
  17. Repair shorted lock-off solenoid relay switch power circuit between relay and fuse. After repairs, go to step  21.
  18. Replace the lock-off relay. After repairs, go to step  21.
  19. Repair short to ground on lock-off solenoid relay switch output circuit between relay and LPL or HPL solenoid. After repairs, go to step  21.
    20. NOTE: When replacing PCM, Bi-fuel (LQ4/KL6) models require a switchover to gasoline with scan tool in order to perform Crankshaft Position Variation Learn Procedure. CNG only (LQ4/KL8) models DO NOT require Crankshaft Position Variation Learn Procedure.
  20. Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
  21. Remove all test equipment except scan tool. Connect any disconnected components, fuses, etc. Using scan tool, clear DTC information from AF ECM and PCM. Turn OFF the ignition and wait 30 seconds. Start engine and operate vehicle. Observe MIL. Observe vehicle's performance and driveability. After operating vehicle, inspect both control modules for stored DTCs. Does vehicle operate on CNG with normal driveability, no MIL illumination, and no stored DTCs? If yes, system is okay. If no, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
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