Practice Exam Questions And Correct

Ohio Exhaust and Emissions Technician Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2025|2026 Q&A | Instant Download Pdf

• What is the primary purpose of a vehicle’s exhaust system?
• To increase engine power
• To reduce emissions and noise
• To circulate coolant
• To store fuel
• To reduce emissions and noise

The exhaust system channels harmful gases away from the engine and reduces both noise and pollutants.

• Which gas is produced in the largest quantity by an internal

combustion engine?

• Nitrogen 1 / 4

• Carbon monoxide
• Carbon dioxide
• Oxygen
• Nitrogen

About 70–75% of exhaust gases are nitrogen, as air is mostly nitrogen.

• What component converts harmful gases into less harmful ones in the

exhaust system?

• Muffler
• Oxygen sensor
• Catalytic converter
• Exhaust manifold

The catalytic converter chemically converts CO, HC, and NOx into CO₂, H₂O, and N₂.

• What is the main function of the oxygen sensor?
• Measure exhaust pressure
• Monitor oxygen levels in exhaust gases
• Measure fuel pressure
• Detect catalytic converter efficiency

The oxygen sensor ensures the engine maintains the proper air–fuel ratio for efficient combustion.

5. A rich air-fuel mixture will cause the oxygen sensor to read:

• High voltage 2 / 4

• Low voltage
• Constant voltage
• No voltage

A rich mixture means less oxygen in exhaust gases, leading to a lower sensor voltage.

• What gas is most associated with smog formation?
• Carbon monoxide
• Hydrocarbons
• Nitrogen oxides (NOx)
• Carbon dioxide

NOx reacts with sunlight and hydrocarbons to form smog.

• What does EGR stand for?
• Exhaust Gas Restriction
• Exhaust Gas Recirculation
• Engine Gas Regulation
• Emission Gauge Response

The EGR system reduces NOx emissions by recirculating exhaust gases into the intake manifold.

• The catalytic converter operates efficiently at what temperature

range?

A. 100–200°F

B. 400–800°F

C. 900–1200°F 3 / 4

• Below freezing

The catalyst requires heat to activate and promote chemical reactions.

• Which emission control system prevents fuel vapors from escaping

into the atmosphere?

• PCV system
• EVAP system
• EGR system
• AIR system

The Evaporative Emission Control System (EVAP) captures and recycles fuel vapors.

• The PCV system helps control what type of emissions?
• Exhaust
• Crankcase
• Evaporative
• Catalyst

The Positive Crankcase Ventilation (PCV) system removes blow-by gases from the crankcase.

• What is the primary pollutant produced by incomplete

combustion?

• Carbon dioxide
• Carbon monoxide
• Nitrogen oxides
• / 4