Emission Control Systems Flashcards

The EGR (Exhaust Gas Recirculation) system primarily reduces which exhaust emission?

Answer: Oxides of nitrogen (NOx)

EGR introduces inert exhaust gases into the intake to lower peak combustion temperatures, which reduces NOx formation.

A stuck-open EGR valve at idle will cause:

Answer: Rough idle and possible stalling

An EGR valve that stays open at idle dilutes the combustible mixture with exhaust gas, causing rough idle and potential stall.

The EVAP (Evaporative Emission Control) system is designed to:

Answer: Prevent fuel vapor from escaping to the atmosphere

The EVAP system captures fuel vapors from the fuel tank and routes them to the intake to be burned rather than released into the air.

A P0442 code (small EVAP leak detected) is set. The FIRST step in diagnosis is:

Answer: Perform a smoke test to locate the leak source

A smoke test is the most reliable and efficient method to locate small EVAP system leaks before replacing parts.

An oxygen sensor that switches slowly between rich and lean is described as:

Answer: Lazy or degraded

A slow-switching O2 sensor is considered lazy or degraded, meaning it no longer responds quickly enough to support accurate closed-loop fuel control.

During a catalyst monitor drive cycle, the downstream O2 sensor switches as frequently as the upstream sensor. This indicates:

Answer: The catalyst efficiency is low and it is failing

A healthy catalyst dampens exhaust gas composition swings, so the downstream sensor should switch far less frequently than the upstream sensor.