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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 System Diagnosis (Bi-Fuel & CNG) >> Diagnostic Procedure

Diagnostic Procedure

NOTE: If DTC sets, causing gasoline operation, check pressure only before DTC sets. If vehicle will not idle on CNG, check cranking pressure. A rhythmic pressure fluctuation of 10-20 psi is normal.
  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. Are AF ECM DTCs P0201-P0208, P0602, P0605 or P1215 set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
  2. Connect vehicle to filling station. Ensure fuel tank is at least 1/3 full. Fill CNG fuel tank if necessary. Observe Fuel Tank Pressure (FTP) sensor data display with scan tool. Does FTP sensor display a pressure at or above 1200 psi (8274 kPa)? If yes, go to next step. If no, go to step  6.
  3. Observe Fuel Rail Pressure (FRP) sensor display with scan tool. Observe FRP sensor display while cranking engine. If engine will not start on CNG, use pressure values observed during cranking. Is FRP sensor value within 40-50 psi (276-345 kPa)? If yes, go to next step. If no, go to step  9. If engine starts on CNG, allow engine to idle until normal operating temperature is obtained. Observe and record FRP sensor display with scan tool. Compare recorded scan tool display pressure values to specification. Is FRP sensor value within 40-50 psi (276-345 kPa)? If yes, go to next step. If no, go to step  9.
  4. Turn ON the ignition with the engine OFF. Observe and record fuel rail pressure immediately after cranking engine for a few seconds. Turn engine OFF if it starts. Monitor fuel rail pressure for 5 minutes. Does fuel rail pressure drop more than 3 psi (21 kPa)? If yes, go to step  13. If no, go to next step.
  5. Turn OFF the ignition. Remove dust cap from pressure test port located on Intermediate Pressure Regulator (IPR). Depress valve core stem in order to relieve CNG fuel pressure from IPR. Using components available within CNG Electronic Pressure Gauge Kit (J 39970), install transducer to adapter with Fuel Test Port Adapter (J 39970-100) onto pressure test port. Connect (J 39970) to (J 39970-100). Connect DMM (J 39200) to (J 39970). Zero DMM (J 39200) using procedure included with (J 39970). Observe fuel pressure with DMM while cranking engine. If engine will not start on CNG, use pressure values observed during cranking. Are all fuel pressure values within 110-210 psi (758-1448 kPa)? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to step  15. If engine does start on CNG, allow engine to idle until normal operating temperature is obtained.
    NOTE: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless fluctuations become excessive.

    Observe and record pressure indicated by DMM at engine idle. Observe and record pressure indicated by DMM during engine load by performing following:

    1. Apply parking brake.
    2. Firmly apply and hold brake pedal.
    3. Place vehicle in forward gear.
    4. Observe pressure while depressing throttle to 75 percent or more for a maximum of 10 seconds.
    5. Allow engine to idle for a minimum of 2 minutes in order to cool transmission.

    Compare recorded pressure values to value range specified. Are all fuel pressure values within 110-210 psi (758-1448 kPa)? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article. If no, go to step  15.

  6. Listen for High Pressure Lock-Off (HPL) solenoid operation as you quickly turn ignition between LOCK and RUN position. Can operation of HPL be heard? If yes, go to next step. If no, go to step  8.
  7. Remove fuel tank cover. Ensure manual tank valve is fully open by turning screw fully counterclockwise. Did you have to open manual tank valve? If yes, go to step  2. If no, go to step  17.
  8. Remove fuel tank cover. Disconnect harness connector of HPL solenoid. Connect Test Light (J 34142-B) between body harness HPL connector terminals. Observe test light as you turn ON the ignition, with the engine OFF. Does test light illuminate for about 2 seconds? If yes, go to step  21. If no, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article for diagnosis of electrical circuits.
  9. Turn OFF the ignition. Remove dust cap from pressure test port located on Intermediate Pressure Regulator (IPR). Depress valve core stem in order to relieve CNG fuel pressure from IPR. Using components available within CNG Electronic Pressure Gauge Kit (J 39970), install transducer to adapter with Fuel Test Port Adapter (J 39970-100) onto pressure test port. Connect (J 39970) to (J 39970-100). Connect DMM (J 39200) to (J 39970). Zero DMM (J 39200) using procedure included with (J 39970). Observe fuel pressure with DMM while cranking engine. If engine will not start on CNG, use pressure values observed during cranking. Is pressure value within 110-210 psi (758-1448 kPa)? If yes, go to step  11. If no, go to next step. If engine does start on CNG, allow engine to idle until normal operating temperature is obtained.
    NOTE: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless fluctuations become excessive.

    Observe and record pressure indicated by DMM at engine idle. Compare recorded pressure value to specification. Is pressure value within 110-210 psi (758-1448 kPa)? If yes, go to step  11. If no, go to next step.

  10. Is fuel pressure greater than 210 psi (1448 kPa)? If yes, go to step  19. If no, go to step  15.
  11. Turn OFF the ignition. Feel Low Pressure Lock-Off (LPL) solenoid as an assistant cranks engine. Can you feel LPL operate as engine is cranking? If yes, go to step  18. If no, go to next step.
  12. Turn OFF the ignition. Disconnect harness connector of LPL solenoid. Connect Test Light (J 34142-B) between engine harness LPL connector terminals. Observe test light as you crank engine. Does test light illuminate during cranking? If yes, go to step  20. If no, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article for diagnosis of electrical circuits.
  13. Inspect for a fuel system leak between LPL solenoid and CNG fuel injectors. Replace any leaking components as necessary. Did you find and correct condition? If yes, go to step  22. If no, go to next step.
  14. Raise CNG fuel rails, lines and injectors as an assembly. Remove IGN E fuse. Crank engine for 5 seconds in order to charge CNG fuel rail with pressure. Locate and replace leaking CNG fuel injector. After repairs, go to step  22.
  15. Inspect fuel line between HPL and HPR and fuel line between HPR and LPL for kinks, bends, damage or obstruction. An obstructed fuel line may be cool or frosted near obstruction when fuel flows through line. Repair or replace components as necessary. Did you find and correct condition? If yes, go to step  22. If no, go to next step.
  16. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under BASIC FUEL SYSTEM CHECKS (CNG) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. Replace CNG in-line filter. Replace HPR filter. Observe fuel pressure with DMM while cranking engine. If engine will not start on CNG, use pressure value observed during cranking. Is fuel pressure value within 110-210 psi (758-1448 kPa)? If yes, go to step  22. If no, go to step  19. If engine does start on CNG, allow engine to idle until normal operating temperature is obtained.
    NOTE: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless fluctuations become excessive.

    Observe and record pressure indicated by DMM at engine idle. Observe and record pressure indicated by DMM during engine load by performing following steps:

    1. Apply parking brake.
    2. Firmly depress and hold brake pedal.
    3. Place vehicle in forward gear.
    4. Observe pressure while depressing throttle to 75 percent or more for a maximum of 10 seconds.
    5. Allow engine to idle for a minimum of 2 minutes in order to cool transmission.

    Compare recorded pressure values to specification. Are all fuel pressure values within 110-210 psi (758-1448 kPa)? If yes, go to step  22. If no, go to step  19.

  17. Replace Fuel Tank Pressure (FTP) sensor. After repairs, go to step  22.
  18. Replace Intermediate Pressure Regulator (IPR). After repairs, go to step  22.
  19. Replace High Pressure Regulator (HPR). After repairs, go to step  22.
  20. Replace Low Pressure Lock-Off (LPL) solenoid. After repairs, go to step  22.
  21. Replace High Pressure Lock-Off (HPL) solenoid. After repairs, go to step  22.
  22. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under BASIC FUEL SYSTEM CHECKS (CNG) in BASIC DIAGNOSTIC PROCEDURES - TRUCKS - EXCEPT TRACKER article. Turn OFF the ignition. Remove all remaining test equipment. Ensure dust cap is installed onto underhood test port. Start and idle engine. Inspect for CNG fuel system leaks between fuel tank and IPR using Ultrasonic Leak Detector (J 41416). Inspect for CNG fuel system leaks at fuel rails and injectors using Snoop® or soapy water. Repair any leaks as necessary. Using scan tool, clear DTC information from AF ECM and from PCM. Turn the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe MIL. Observe vehicle performance and driveability. Does vehicle operate on CNG with normal driveability and no MIL illumination? 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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