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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 Unwanted Switch To Gasoline (Bi-Fuel Only) >> 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. Crank or idle engine for 10 seconds. Observe Diagnostic Trouble Code (DTC) information from AF ECM with scan tool. Does scan tool display DTC P0201-P0208, P0602, P0605 or P1215 failed this ignition? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, go to next step.
  3. Observe Fuel Indicator Lamp (FIL) while engine is running. Is FIL illuminated? If yes, go to step  5. If no, go to next step.
  4. Condition is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article. Is their a system operation concern? If yes, 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. If no, system is okay.
  5. With scan tool, communicate with AF ECM and observe AFO Signal and AFO Signal Command data displays. Observe displays as you crank and start engine. Do data displays indicate AF ECM is in control of engine fueling? If yes, go to FUEL INDICATOR LAMP ALWAYS ON - ALTERNATIVE FUELS . If no, go to next step.
  6. Do both displays indicate the same information? If yes, go to next step. If no, go to DTC P1215 under DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article.
  7. Turn OFF the ignition. Disconnect harness connector of a CNG fuel injector. Turn ON the ignition, with the engine OFF. Probe Ignition Feed circuit of CNG fuel injector with a test light connected to a known good ground. Does test light illuminate? If yes, go to next step. If no, go to FUEL INJECTOR CIRCUIT DIAGNOSIS (BI-FUEL & CNG) 
    8. NOTE: Before proceeding with Fuel Tank Pressure (FTP) sensor diagnosis, ensure manual lock-down screw of HPL manual shut-off fitting is open by rotating screw counterclockwise until fully seated.
  8. Verify CNG fuel tank is at full pressure by connecting vehicle to a CNG dispensing station and filling CNG fuel tank. Turn ON the ignition, with the engine OFF. Observe FTP scan tool data display. Is FTP sensor accurately indicating fuel pressure? If yes, go to next step. If no, go to FUEL GAUGE INACCURATE OR INOPERATIVE - ALTERNATIVE FUELS .
  9. Turn the ignition OFF and wait 15 seconds. Turn ON the ignition, with the engine OFF. With scan tool, communicate with AF ECM and observe Fuel Rail Pressure (FRP) sensor data display. Observe FRP data display while cranking engine. Does FRP data display ever indicate fuel pressure more than 40 psi (276 kPa)? If yes, go to next step. If no, go to FUEL INJECTOR CIRCUIT DIAGNOSIS (BI-FUEL & CNG) .
    10. NOTE: A higher secondary ignition voltage is required to operate engine on Alternative Fuel than on gasoline. A vehicle that operates normally on gasoline, does not indicate a fully functional ignition system.
  10. Inspect ignition system for proper voltage output using Spark Tester (J 26792). Remove and inspect spark plugs for wet (fouled) plugs, cracks, excessive wear, incorrect gap, burned electrodes or heavy deposits. Inspect spark plug wires for damage. Spray secondary ignition with a water bottle, and check for crossfire or missing. Inspect AF ECM and PCM grounds for being clean, tight, and properly located. Repair as necessary. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  11. Replace AF ECM. After repairs, go to next step.
  12. Connect any disconnected components, fuses, etc. With scan tool, clear DTC Information from AF ECM and PCM. Turn the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe FIL and MIL. Observe vehicle performance and driveability. After operating vehicle, inspect AF ECM and PCM for stored DTCs. Does vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs? If yes, system is okay. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article, or see SYMPTOM DIAGNOSIS under SYMPTOMS (BI-FUEL & CNG) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
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