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 properly working three-way catalytic converter, how should the downstream O2 sensor signal look compared with the upstream sensor?
Answer: Relatively steady with little switching
A healthy converter stores oxygen, so the downstream sensor signal stays fairly steady.
A P0420 code indicates what?
Answer: Catalyst efficiency below threshold (Bank 1)
P0420 sets when the PCM finds Bank 1 catalyst efficiency below the required threshold.
Which condition is most likely to overheat and damage a catalytic converter?
Answer: A persistent engine misfire
Unburned fuel from misfires burns inside the converter, which can overheat and melt the substrate.
A restricted catalytic converter can be confirmed by which test?
Answer: Exhaust back-pressure test at the upstream O2 sensor port
High back pressure measured ahead of the converter, especially at 2500 RPM, points to a restriction.
A typical acceptable maximum exhaust back pressure at 2500 RPM is about:
Answer: 1.5 psi
Most manufacturers allow about 1.5 psi or less at 2500 RPM; higher readings mean a restriction.
Which component in a three-way converter makes oxygen storage possible?
Answer: Cerium oxide
Cerium in the washcoat stores and releases oxygen to help oxidation and reduction reactions.
Before replacing a catalytic converter for a P0420, what should a technician do first?
Answer: Fix any misfires, exhaust leaks, or fuel control problems
Root causes such as misfires, exhaust leaks, or rich conditions must be fixed, or the new converter will fail too.