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Home >> Cadillac >> 2002 >> Escalade EXT >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Ignition System >> Ignition Relay Diagnosis (5.7L Bi-Fuel) >> Diagnostic Procedure
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Diagnostic Procedure

  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
  2. Turn the ignition ON, with the engine OFF. Inspect CNG, ECM 1 and TRANS fuses. Is any fuse open? If yes, go to step  15. If no, go to next step.
  3. Probe both terminals of each fuse using Test Light (J 34142-B) connected to a known good ground. Ensure that ignition is ON and engine is OFF. With fuses installed, the probe test points for fuses are visible at either side of amperage rating. Does test light illuminate at all terminals? If yes, go to step  5. If no, go to next step.
  4. Inspect fuse terminal contact. Repair fuse terminal contact as necessary. Test fuse supply source. Typically, source is a MAXI fuse, fusible link or a relay. Repair fuse supply source as necessary. After repairs, go to step  24.
  5. Using scan tool, attempt to communicate and retrieve data from AF ECM. Does scan tool display Alternative Fuels ECM data? If yes, go to step  8. If no, go to next step.
  6. Turn the ignition OFF. Disconnect AF ECM connectors. Turn the ignition ON leaving the engine OFF. Probe battery power and ignition power circuit terminals at AF ECM connectors with (J 34142-B) connected to a known good ground. Does test light illuminate at all terminals? If yes, go to next step. If no, go to step  16.
  7. Probe all AF ECM ground circuit terminals at ECM connector with (J 34142-B) connected to battery positive. Does test light illuminate at all terminals? If yes, go to step  22. If no, go to step  16.
  8. Observe fuel gauge select switch data parameter on scan tool. Depress and release fuel gauge select switch. Did fuel gauge select switch data parameter indicate APPLIED when switch was depressed? If yes, go to step  10. If no, go to next step.
  9. With the ignition ON, backprobe ignition relay switch load terminal No. 87 with (J 34142-B) connected to a known good ground. Is test light illuminated? If yes, go to FUEL GAUGE RELAY DIAGNOSIS - ALTERNATIVE FUELS in appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. If no, go to step  12.
  10. Observe Alternative Fuels engine speed data parameter on scan tool. Observe engine speed parameter as you crank and attempt to start engine. Is engine RPM displayed as you crank or start engine? If yes, go to next step. If no, go to DTC P0336: CRANKSHAFT POSITION (CKP) SENSOR PERFORMANCE under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA article.
  11. With the ignition ON, backprobe ignition relay switch load terminal No. 87 with (J 34142-B) connected to a known good ground. Observe test light as you turn ignition OFF. Is test light illuminated with ignition OFF? If yes, go to step  17. If no, system is okay.
  12. With the ignition ON, backprobe ignition relay switch supply terminal No. 30 with (J 34142-B) connected to a known good ground. Is test light illuminated? If yes, go to next step. If no, go to step  18.
  13. With the ignition ON, backprobe ignition relay coil supply terminal No. 85 with (J 34142-B) connected to a known good ground. Is test light illuminated? If yes, go to next step. If no, go to step  19.
  14. Disconnect ignition relay connector. With ignition on, connect (J 34142-B) between ignition relay coil supply terminal No. 85 and ignition relay coil ground terminal No. 86. Is test light illuminated? If yes, go to step  21. If no, go to step  20.
  15. Test for short that caused fuse to open. Possible shorts include the following:

    CNG Fuse

    • A shorted fuel gauge select switch circuit.
    • A shorted lock-off or fuel solenoid or circuit.
    • A shorted AF ECM or AF ECM battery power circuit.

    ECM 1 Fuse

    • A shorted ignition relay coil or circuit.
    • A shorted base vehicle circuit. See POWER DISTRIBUTION article in WIRING DIAGRAMS.

    TRANS Fuse

    • A shorted AF ECM or AF ECM ignition power circuit.
    • A shorted base vehicle circuit. See POWER DISTRIBUTION article in WIRING DIAGRAMS.

    Repair circuits or replace components as necessary. After repairs, go to step  24.

  16. Repair open in AF ECM circuit that did not illuminate test light. After repairs, go to step  24.
  17. Replace stuck ignition relay or repair ignition power circuit shorted to battery positive. After repairs, go to step  24.
  18. Repair open in ignition relay switch supply circuit between relay and circuit splice. After repairs, go to step  24.
  19. Repair open in ignition relay coil supply circuit between relay and circuit splice. After repairs, go to step  24.
  20. Repair open in ignition relay coil ground circuit between relay and ground. After repairs, go to step  24.
  21. Replace ignition relay. After repairs, go to step  24.
  22. Inspect for proper AF ECM terminal contact. Test for an open Class 2 serial data circuit between splice and AF ECM connector terminal. Repair terminal contact or wiring as necessary. Was terminal contact or a wiring repair performed? If yes, go to step  24. If no, go to next step.
  23. Replace AF ECM. Program replacement AF ECM. See ALTERNATIVE FUEL ENGINE CONTROL MODULE under PROGRAMMING in SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA - BI-FUEL article. After repairs, go to next step.
  24. 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 the ignition OFF and wait 30 seconds. Start engine and operate vehicle. Observe Fuel Indicator Light (FIL) and MIL. Observe vehicle performance and driveability. After operating vehicle, inspect BOTH control modules 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, perform ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTICS - 5.7L CHEVY EXPRESS & SAVANA - BI-FUEL article.
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