ASE L2 Domain 5: Emissions Systems Diagnosis Welcome to your ASE L2 Domain 5: Emissions Systems Diagnosis 1. ASE L2: Emissions Systems Diagnosis A diesel engine equipped with an SCR (Selective Catalytic Reduction) system consistently has high NOx emissions under load. The DEF "Diesel Exhaust Fluid" quality is confirmed to be within specification. What should be checked next? A. DEF injector operation and spray pattern B. EGR (Exhaust Gas Recirculation) valve operation C. Turbocharger boost pressure D. Particulate filter back pressure None 2. ASE L2: Emissions Systems Diagnosis A technician finds a DPF (Diesel Particulate Filter) pressure differential sensor reading higher than expected on a light load. What is the MOST likely cause of this issue? A. DPF is approaching the end of its service life. B. A hole in the DPF substrate. C. Incorrect reading from the differential pressure sensor. D. A leak in the exhaust upstream of the DPF. None 3. ASE L2: Emissions Systems Diagnosis An engine's exhaust gas recirculation (EGR) system is suspected of contributing to reduced engine performance. The EGR cooler has passed a pressure test. What is the NEXT best step to diagnose the issue? A. Check for EGR valve sticking or improper operation. B. Perform a compression test on all cylinders. C. Test the intake manifold for leaks. D. Inspect the air filter for clogging. None 4. ASE L2: Emissions Systems Diagnosis A diesel engine is found to emit blue smoke at all operating temperatures. Which component should be inspected FIRST for diagnosis? A. EGR valve B. Oil separator C. DPF system D. Turbocharger seals None 5. ASE L2: Emissions Systems Diagnosis During the forced regeneration of a DPF, the exhaust temperature fails to reach the temperature required to initiate the burn-off. Which of the following could be responsible for this issue? A. Faulty intake air temperature sensor B. Insufficient fuel pressure to the doser/injector C. Malfunctioning coolant temperature sensor D. Blocked air cleaner element None 6. ASE L2: Emissions Systems Diagnosis A technician is diagnosing a diesel engine that has passed all NOx reduction tests but fails for HC (Hydrocarbon) emissions. What is the most likely cause? A. Ineffective EGR cooler B. Failing oxygen sensor C. Leaking injectors D. Overactive DEF system None 7. ASE L2: Emissions Systems Diagnosis A technician is unable to perform a stationary regeneration on a diesel particulate filter despite multiple attempts and no diagnostic trouble codes present. What is the most likely cause? A. DEF level is too low. B. High altitude operation. C. Faulty DPF differential pressure sensor. D. Battery voltage is insufficient. None 8. ASE L2: Emissions Systems Diagnosis After servicing a diesel engine's aftertreatment system, the technician notices excessive soot production during post-service testing. What could be the cause? A. DEF nozzle misalignment B. Incorrectly installed DPF gaskets C. Insufficient turbocharger boost D. Miscalibrated mass airflow sensor None 9. ASE L2: Emissions Systems Diagnosis When monitoring live data on a diesel engine, a technician observes that the NOx sensor downstream of the SCR system shows a higher reading than the upstream sensor under steady cruising conditions. What does this suggest? A. The DEF quality is substandard. B. There is a fault in the upstream NOx sensor. C. The SCR catalyst efficiency is reduced. D. Exhaust temperature is too low for proper SCR function. None 10. ASE L2: Emissions Systems Diagnosis A diesel engine vehicle equipped with a DOC (Diesel Oxidation Catalyst) is experiencing higher than normal exhaust temperatures. What is the MOST likely cause? A. Excessive DEF dosing ahead of the DOC B. A damaged DOC substrate C. An over-fueling condition D. Low ambient temperatures affecting the exhaust system None 1 out of 10 Time is Up! Time's up
