ASE A9 Air Induction and Exhaust Systems

Question 1

On a diesel engine equipped with a diesel particulate filter (DPF), which input does the ECM primarily use to estimate how much soot has accumulated in the filter?

Accepted Answer

Differential pressure across the DPF inlet and outlet

Answer

As soot loads the filter, exhaust flow is restricted, so the pressure difference between the DPF inlet and outlet rises. The ECM uses this differential pressure, along with modeled soot calculations, to decide when a regeneration is needed.

Question 2

Diesel exhaust fluid (DEF) used in SCR systems is made of which mixture?

Accepted Answer

32.5% urea and 67.5% deionized water

Answer

DEF is a solution of about 32.5% high-purity urea in 67.5% deionized water. This concentration gives the lowest freezing point for a urea-water mixture.

Question 3

Approximately at what temperature does standard DEF begin to freeze?

Accepted Answer

12°F (-11°C)

Answer

A 32.5% urea solution freezes at about 12°F (-11°C). SCR systems therefore use heated DEF tanks and lines to thaw it in cold weather.

Question 4

A turbocharger with variable geometry vanes has vanes stuck in the fully open position. Which complaint is most likely?

Accepted Answer

Low boost and sluggish response at low engine speeds

Answer

Open vanes make the turbine nozzle larger, which lowers exhaust gas velocity across the turbine. The result is low boost and poor response at low rpm.

Question 5

A diesel engine is losing coolant with no external leaks, and white exhaust smoke is present after startup. The engine has a cooled EGR system. Which component is the most likely source?

Accepted Answer

A leaking EGR cooler

Answer

An internal leak in the EGR cooler lets coolant enter the exhaust gas stream and then the intake. That produces coolant loss and white smoke.

ASE A9 Practice Test

ASE A9 Practice Test

ASE A9 Air Induction and Exhaust Systems