ASE L2 study guide
ASE L2 · Work through your exam, one topic at a time.
ASE L2 - Electronic Diesel Engine Diagnosis Specialist is an advanced-level certification test in the ASE certification test series, administered by the National Institute for Automotive Service Excellence (ASE). It is aimed at experienced diesel technicians who already diagnose with scan tools, service information and lab scopes, and who want a credential that verifies their ability to troubleshoot electronically controlled diesel engines rather than to perform routine mechanical repair. The ASE L2 study guide has 5 sections and about 1,762 words.
01General Diesel Engine Diagnosis: Mechanical Baseline First
A diesel makes power from the heat of compression, so a cylinder that cannot seal will not fire no matter how well the fuel system performs. Before you chase codes or pull injectors, establish the mechanical condition: cranking compression (direct gauge or relative compression through cranking-speed data), cylinder leakdown, crankcase blowby, oil pressure, and valvetrain condition.
371 words, about 2 min02Diesel Engine Controls and Electronic Systems Diagnosis
The ECM decides fueling and timing from crankshaft and camshaft position, boost and intake air temperature, coolant temperature, oil pressure, rail or injection control pressure, throttle (accelerator pedal) position, and vehicle speed. It commands injectors, the high-pressure fuel control actuator, EGR valve, variable-geometry turbo actuator, fan, and aftertreatment devices.
360 words, about 2 min03Air Induction, Turbocharger and Exhaust System Diagnosis
Diagnose airflow in order: air filter and restriction indicator, intake piping, turbocharger compressor, charge air cooler and boots, intake manifold, then the exhaust side - turbine, exhaust piping, and any aftertreatment restriction. Restriction on the intake side shows up as low boost, black smoke, and low power; restriction on the exhaust side shows up as high exhaust backpressure, poor boost, and elevated temperatures.
360 words, about 2 min04Diesel Fuel System and Injection Diagnosis
Separate the system into transfer (lift) pump, filters and water separator, and the high-pressure side - rail or injection control pressure, pressure control valve or metering valve, high-pressure lines, and injectors. Air in the suction side causes hard starting, rough running, and low rail pressure.
329 words, about 2 min05Emission Control and Aftertreatment System Diagnosis
Cooled EGR lowers combustion temperature and nitrogen oxides; a leaking EGR cooler causes coolant loss and white vapor. The diesel oxidation catalyst burns hydrocarbons and carbon monoxide and converts NO to NO2.
342 words, about 2 min