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
A vehicle sets a P0401 (EGR flow insufficient) code. Which condition is the most likely cause?
Answer: Carbon-clogged EGR passages in the intake
Carbon buildup restricts exhaust gas flow through the EGR passages, causing an insufficient-flow code.
An EGR valve that is stuck open at idle will most likely cause which symptom?
Answer: Rough idle or stalling
Exhaust gas entering the intake at idle dilutes the mixture and causes a rough idle or stall.
The primary purpose of the EGR system is to reduce which emission?
Answer: Oxides of nitrogen (NOx)
EGR lowers peak combustion temperatures, which reduces NOx formation.
Technician A says a failed EGR system can cause spark knock (detonation). Technician B says it can cause high NOx readings. Who is correct?
Answer: Both A and B
Without EGR, combustion temperatures rise, which causes both detonation and increased NOx.
On a vehicle with a digital (linear) EGR valve, how does the PCM confirm the valve's position?
Answer: A pintle position sensor on the valve
Linear EGR valves have a built-in position sensor that reports pintle position to the PCM.
A DPFE sensor is used on some Ford EGR systems to measure what?
Answer: Pressure difference across an orifice in the EGR tube
The Differential Pressure Feedback EGR sensor calculates EGR flow from the pressure drop across a metering orifice.
When testing a vacuum-operated EGR valve with a hand vacuum pump at idle, what result shows the valve and passages are working?
Answer: Engine idle becomes rough or stalls
Opening the EGR valve at idle lets exhaust into the intake, so a good valve and open passages cause a noticeable rough idle.