Fuel Systems & 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 Fuel Systems & Emissions Control flashcards as text
Which emission does the catalytic converter's reduction catalyst (rhodium) primarily target?
Answer: NOx (oxides of nitrogen)
Rhodium acts as a reduction catalyst by stripping oxygen atoms from NOx molecules, converting them into harmless nitrogen (N2) and oxygen (O2) gases.
How does a wideband oxygen sensor differ from a conventional narrowband sensor?
Answer: It measures air-fuel ratios across a broad range rather than only switching rich/lean
A wideband sensor produces a linear voltage or current output across a wide lambda range (approximately 0.65–1.6 lambda), while a narrowband sensor switches abruptly between rich and lean signals near stoichiometry.
What condition does OBD-II diagnostic trouble code P0420 indicate?
Answer: Catalyst system efficiency is below the acceptable threshold
P0420 is set when the downstream oxygen sensor switches in a pattern similar to the upstream sensor, indicating the catalyst is no longer storing and releasing oxygen efficiently and has degraded.
What is the role of the fuel tank pressure (FTP) sensor in the EVAP system?
Answer: Monitor tank pressure to detect leaks during EVAP diagnostic tests
The FTP sensor monitors pressure and vacuum changes inside the sealed EVAP system during self-tests; if the system cannot hold vacuum or pressure, a leak is detected and a DTC is stored.
When diagnosing a fuel-related no-start condition, what should be checked FIRST?
Answer: Fuel pressure at the fuel rail using a pressure gauge
Confirming adequate fuel pressure at the rail verifies that the pump is operational and delivering sufficient pressure; without this baseline, no further fuel system diagnosis is meaningful.
What does a MAP (Manifold Absolute Pressure) sensor measure?
Answer: Absolute pressure inside the intake manifold referenced to a perfect vacuum
The MAP sensor measures intake manifold pressure in absolute terms (referenced to zero pressure), which the ECM uses to calculate engine load and determine the appropriate fuel delivery and ignition timing.
Which condition would MOST LIKELY cause a vehicle to fail an emissions inspection for excessive HC (hydrocarbon) output?
Answer: Misfiring cylinders sending unburned fuel through the exhaust
Cylinder misfires allow raw, unburned fuel (hydrocarbons) to pass directly through the exhaust system and out the tailpipe, dramatically elevating HC readings at the tailpipe probe.