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Maintenance and Troubleshooting Flashcards

7 cards from real CNG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Maintenance and Troubleshooting flashcards as text

  1. Which solution is the approved method for field-testing CNG fuel line fittings for leaks?

    Answer: Soapy water or approved leak detection solution

    Approved leak detection fluid (soapy water or commercial solution) is applied to fittings; bubbles indicate a leak without ignition risk.

  2. A CNG vehicle's high-pressure regulator is suspected of failing. Which symptom most directly points to a regulator malfunction?

    Answer: Consistently low fuel pressure delivered to the engine

    A failing high-pressure regulator cannot step down tank pressure correctly, resulting in consistently low delivery pressure to the engine.

  3. When inspecting CNG high-pressure cylinders, what condition requires the cylinder to be immediately removed from service?

    Answer: Any visible crack, gouge, or deep abrasion on the cylinder

    Any crack, gouge, or deep abrasion compromises cylinder structural integrity and mandates immediate removal from service per NFPA 52 and NGV2 standards.

  4. After replacing a CNG fuel filter, what must be done before returning the vehicle to service?

    Answer: Perform a full leak test on all disturbed connections

    Any time a fuel system component is opened and reassembled, a leak test on all disturbed fittings and connections is mandatory before returning to service.

  5. A CNG technician notices the pressure relief device (PRD) has vented. What is the correct first diagnostic step?

    Answer: Check if the vehicle was exposed to an external heat source or fire

    PRD venting is a safety event; the technician must determine if excessive heat or fire caused the activation before replacing the device.

  6. What is the most common cause of premature fuel filter clogging in a CNG system?

    Answer: Moisture and compressor oil carryover from low-quality fill stations

    Poor-quality CNG from stations with inadequate drying can carry moisture and compressor oil that rapidly clog downstream fuel filters.

  7. Which tool is essential when torquing CNG high-pressure fittings during maintenance?

    Answer: Calibrated torque wrench set to manufacturer specifications

    High-pressure CNG fittings must be torqued to exact manufacturer specifications using a calibrated torque wrench to prevent leaks or thread damage.