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Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Pontiac Sunfire, 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, and 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Engine Controls (Alternative Fuels). If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS (ALTERNATIVE FUELS) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - BI-FUEL - CNG/GASOLINE article.
  2. Observe the Engine Coolant Temperature (ECT) parameter using a scan tool. Is the ECT value 50-90°F (10-32°C)? If yes, go to next step. If no, go to step  4.
    3. NOTE: Calibrate the DMM and test leads to zero ohms to prevent misdiagnosis.
  3. Measure the resistance of each CNG fuel injector using a DMM. Do any of the fuel injectors display a resistance outside 1-2 ohms? If yes, go to step  6. If no, go to DIAGNOSTIC AIDS .
  4. Measure the resistance of each CNG fuel injector using a DMM. Record each fuel injector value. Subtract the lowest resistance value from the highest resistance value. Is the difference equal to, or less than, 0.5 ohm? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
  5. Add all of the CNG fuel injector resistance values, to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors, to obtain an average resistance value. Subtract the lowest, and the highest, individual fuel injector resistance values from the average resistance value. Replace the CNG fuel injector that displays the greatest resistance difference, above or below the average. After repair, go to step  7.
  6. Replace the fuel injector or fuel injectors that are out of the specified range. After repair, go to step  7.
  7. Operate the system to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step  2.
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