Smog Repair Technician Practice Exam 2025 – Complete Test Prep

A faulty mass airflow sensor significantly impacts emissions by causing an increase in carbon monoxide (CO) and hydrocarbon (HC) emissions. The mass airflow sensor measures the amount of air entering the engine’s intake, which is critical for the engine control unit (ECU) to determine the correct amount of fuel to inject for optimal combustion.

When the mass airflow sensor is malfunctioning, it may send incorrect data to the ECU, resulting in an incorrect air-fuel mixture. If the engine runs too rich (more fuel than air), it can lead to incomplete combustion. This incomplete combustion is a primary source of increased CO and HC emissions.

High CO emissions occur because the excess fuel does not fully combust, leading to carbon monoxide as a byproduct. Increased HC emissions arise from unburned fuel entering the exhaust system. Proper function of the mass airflow sensor is essential for maintaining the right air-fuel mixture and, consequently, for minimizing harmful exhaust emissions.