LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2002 >> Escalade EXT >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures >> Basic Fuel System Checks (Gasoline) >> Fuel System Pressure Test (4.8L, 5.3L, 6.0L & 8.1L) >> Diagnostic Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedure

  1. Perform OBD system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS or SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article. After performing OBD system check, go to next step.
    2. NOTE: Inspect fuel system for damage, or external leaks, before proceeding with this test.
  2. Turn ignition on, with engine off. Using scan tool, command fuel pump ON. If fuel pump operates, go to next step. If fuel pump does not operate, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS under FUEL SYSTEMS (GASOLINE) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.
    3. NOTE: Ensure there is adequate fuel in fuel tank before proceeding with this test.
  3. Turn ignition off. Ensure all accessories are off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Install Fuel Pressure Gauge (J-34730-1A). Place fuel pressure gauge bleed hose into an approved gasoline container. Turn ignition on. Using scan tool, command fuel pump ON. Bleed air from fuel pressure gauge. It may be necessary to command fuel pump ON several times to obtain highest fuel pressure possible. DO NOT start engine. Observe fuel pressure with fuel pump operating. Fuel pressure should be 55-62 psi (385-425 kPa) VIN V, T, U or 48-54 psi (335-375 kPa) VIN Z. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, go to step  12.
    4. NOTE: Fuel pressure may vary slightly when fuel pump stops. After fuel pump stops, fuel pressure should stabilize and remain constant.
  4. Monitor fuel pressure for one minute after fuel pump stops operating. If fuel pressure decreases more than 5 psi (34 kPa) in one minutes, go to step  9. If fuel pressure does not decrease more than 5 psi (0.3 kg/cm2 ) in 10 minutes, go to next step.
  5. Relieve fuel pressure until pressure is 10 psi (69 kPa). Monitor fuel pressure gauge for 5 minutes. If fuel pressure decreases more than 2 psi (14 kPa) in 5 minutes, go to step  24. If fuel pressure decreases 2 psi (14 kPa) or less in 5 minutes, go to next step.
  6. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Monitor fuel pressure gauge. Start engine. If fuel pressure decreases 3-10 psi (21-69 kPa) when engine is started, go to next step. If fuel pressure does not decrease 3-10 psi (21-69 kPa) when engine is started, go to step  8.
  7. Operate vehicle within conditions of customer's concern. Using scan tool, monitor fuel related parameters. If any scan tool parameters indicate a lean condition, go to step  16. If no scan tool parameters indicate a lean condition, go to SYMPTOMS (GASOLINE) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
  8. Disconnect vacuum hose from fuel pressure regulator. Monitor fuel pressure gauge. Start engine and allow it to idle. Using a hand-held vacuum pump, apply vacuum (12-14 in. Hg) to fuel pressure regulator. If fuel pressure decreases by 3-10 psi (21-69 kPa), go to step  21. If fuel pressure does not decrease by 3-10 psi (21-69 kPa), go to step  23.
  9. Turn ignition off. Remove vacuum hose from fuel pressure regulator. Turn ignition on, with engine off. Using scan tool, command fuel pump ON. Inspect for a fuel leak from fuel pressure regulator vacuum port. If fuel pressure regulator is leaking fuel, go to step  23. If fuel pressure regulator is not leaking fuel, go to next step.
  10. Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect fuel feed hose and fuel return hose from fuel rail pipes. Install Fuel Line Shutoff Adapters (J-37287) between fuel hoses and fuel rail pipes. Open both valves on shutoff adapters. Turn ignition on, with engine off. Using scan tool, command fuel pump ON and then OFF. Close shutoff valve at fuel feed line. Monitor fuel pressure gauge for one minute. If fuel pressure remains constant, go to step  19. If fuel pressure does not remain constant, go to next step.
  11. Turn ignition off. Open shutoff valve at fuel feed line. Turn ignition, with engine off. Using scan tool, command fuel pump On and then OFF. Close shutoff valve at fuel return line. Monitor fuel pressure gauge for one minute. If fuel pressure remains constant, go to step  23. If fuel pressure does not remain constant, go to step  20.
  12. If fuel pressure is greater than 62 psi (427 kPa) VIN V, T, U or 54 psi (375 kPa) VIN Z, go to step  14. If fuel pressure is 62 psi (427 kPa) VIN V, T, U or 54 psi (375 kPa) VIN Z or less, go to next step.
  13. If fuel pressure is greater than zero psi, go to step  16. If fuel pressure is zero psi, go to step  17
  14. Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect fuel return hose from fuel rail return pipe. Attach flexible fuel hose to fuel rail outlet passage. Place other end of flexible hose into an approved gasoline container. Turn ignition on, with engine off. Monitor fuel pressure gauge while fuel pump is operating. If fuel pressure is 55-62 psi (385-425 kPa) VIN V, T, U or 48-54 psi (335-375 kPa) VIN Z, go to step  22. If fuel pressure is not as specified, go to next step.
  15. Inspect fuel rail return pipe and fuel rail outlet passage for restriction. Repair as necessary. After repairs, go to step  25. If no restriction is found, go to step  23.
  16. Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect fuel return hose from fuel rail return pipe. Install Fuel Line Shutoff Adapters (J-37287) between fuel return pipe and fuel rail. Open valve on shutoff adapter at fuel pipe. Turn ignition on, with engine off. Using scan tool, command fuel pump ON. Bleed air from fuel system. Monitor fuel pressure gauge. Gradually close valve on shutoff adapter at fuel return pipe. Using scan tool, command fuel pump ON. If fuel pressure increases to more than 62 psi (427 kPa) VIN V, T, U or 54 psi (375 kPa) VIN Z, go to step  23. If fuel pressure does not increase to more than 62 psi (427 kPa) VIN V, T, U or 54 psi (375 kPa) VIN Z, go to next step.
  17. Inspect fuel filter and fuel feed pipe for restriction. Repair as necessary. After repairs, go to step  25. If no restriction is found, go to next step.
  18. Inspect harness connectors and ground circuits of fuel pump for poor connections. Repair as necessary. After repairs, go to step  25. If connectors and ground circuits are okay, go to next step.
  19. Remove fuel sending unit assembly. Inspect fuel pump flex hose for damage, in tank fuel pump harness connectors for poor connections, fuel strainer for a restriction and for contaminates in fuel tank. Repair as necessary. After repairs, go to step  25. If no problem is found, go to step  24.
  20. Turn ignition off. Loosen and raise fuel rail with fuel lines connected. Turn ignition on, with engine off. Using scan tool, command fuel pump ON. Locate and replace leaking fuel injector. After repairs, go to step  25.
  21. Locate and repair loss of vacuum to fuel pressure regulator. After repairs, go to step  25.
  22. Locate and repair restriction in fuel return line. After repairs, go to step  25.
    23. NOTE: Check for a missing or damaged fuel pressure regulator "O" ring before replacing fuel pressure regulator.
  23. Replace fuel pressure regulator. After repairs, go to step  25.
  24. Replace fuel pump assembly. After repairs, go to next step.
  25. Operate system to verify repair. If condition has been corrected, system is okay. If system is not okay, repeat step  3.
scientia non olet · About LEMON Manuals