Emissions Control Flashcards
7 cards from real ASE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Emissions Control flashcards as text
On a diesel vehicle, what does the SCR system inject to reduce NOx?
Answer: Diesel Exhaust Fluid (urea solution)
SCR systems inject DEF, a urea and water solution, which turns NOx into nitrogen and water across a catalyst.
A diesel particulate filter (DPF) is cleaned during normal operation through what process?
Answer: Regeneration by burning off soot at high temperature
During regeneration, exhaust temperatures rise high enough to oxidize collected soot into ash and CO2.
A secondary air injection (AIR) system pumps fresh air into the exhaust mainly during which period?
Answer: Cold start and warm-up
AIR adds oxygen during warm-up to burn HC and CO and to heat the converter faster.
A stuck-closed PCV valve may result in which condition?
Answer: Oil leaks from increased crankcase pressure
Without crankcase ventilation, pressure builds up and pushes oil past seals and gaskets.
In five-gas analysis, high HC with normal CO usually points to what problem?
Answer: Ignition misfire
A misfire sends unburned fuel (HC) out the exhaust without raising CO, because the mixture itself isn't rich.
Which OBD-II readiness monitor is typically non-continuous and needs a specific drive cycle to complete?
Answer: Catalyst monitor
The catalyst monitor runs only under certain conditions during a drive cycle; misfire, fuel, and component monitors run continuously.
In five-gas analysis, high O2 and low CO in the exhaust usually indicate what?
Answer: Lean condition or exhaust leak
Extra oxygen with little CO means too much air, either from a lean mixture or air drawn in through an exhaust leak.