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
A CNG vehicle experiences hard starting in cold weather. Which maintenance item should be inspected first?
Answer: Low-pressure fuel filter and regulator heating element or coolant lines
Cold-weather hard starting on CNG vehicles is commonly caused by a failed regulator heater or blocked coolant line that prevents the regulator from vaporizing fuel properly.
What does a persistently illuminated 'Check Fuel' or 'Fuel System' warning light on a CNG vehicle most commonly indicate?
Answer: A fault detected by the ECM in the CNG fuel delivery circuit
The ECM continuously monitors CNG system sensors; a persistent warning light indicates a stored fault code that requires diagnostic scan tool retrieval.
How often should CNG vehicle high-pressure fuel lines be visually inspected for chafing, kinks, or abrasion?
Answer: At every scheduled preventive maintenance interval
Visual inspection of high-pressure fuel lines should occur at every scheduled PM interval to catch chafing or abrasion before a high-pressure failure develops.
A CNG technician finds water in the fuel filter bowl. What corrective action addresses the root cause?
Answer: Notify the fleet to avoid the fueling station suspected of wet gas and replace the filter
Water in the filter indicates the fueling station's dryer is inadequate; alerting the fleet and avoiding that station addresses the source, not just the symptom.
Which component is inspected to verify the automatic cylinder valve (ACV) is functioning correctly?
Answer: Downstream fuel pressure drop rate when the ignition is turned off
A properly functioning ACV closes when the ignition is off; technicians verify this by monitoring whether downstream pressure drops to zero after key-off.
What is the correct procedure when a CNG vehicle's cylinder reaches its hydrostatic retest date?
Answer: Remove the cylinder from service and send it to a certified test facility
Cylinders past their retest date must be removed from service and sent to a DOT/TC-certified hydrostatic test facility — field retest is not authorized.
A technician smells natural gas near the engine compartment after a routine maintenance. What is the immediate action?
Answer: Eliminate ignition sources, close all cylinder valves, and ventilate the area
Natural gas leaks require immediate elimination of ignition sources and ventilation; manual cylinder valve closure isolates the fuel source before any investigation.