Take ASE S2 Diesel Engines (School Bus) Practice Questions - ASE S2 - Diesel Engines (School Bus) Certification Exam

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ASE S2 Diesel Engines (School Bus) Practice Questions - ASE S2 - Diesel Engines (School Bus) Certification ExamPractice mode

Question 1 of 25

QUESTION 1 / 25

A school bus with a Cummins ISB diesel engine cranks normally but will not start, and the technician confirms there is no fuel reaching the high-pressure pump. Which check should be performed FIRST?

Choose one answer below.

AReplace the high-pressure common-rail pump✓BReplace all fuel injectors as a set✓CIncrease the rail pressure relief valve setting✓DInspect the low-pressure (lift/transfer) supply circuit and primary fuel filter for restriction✓

0 of 25 answered

A school bus with a Cummins ISB diesel engine cranks normally but will not start, and the technician confirms there is no fuel reaching the high-pressure pump. Which check should be performed FIRST?

Technician A says low engine compression on one cylinder can cause hard starting and a miss. Technician B says a cylinder cutout (power balance) test can help isolate a weak cylinder on an electronically controlled diesel. Who is correct?

A school bus diesel produces excessive black smoke under acceleration but idles cleanly. The MOST likely cause is:

During a cylinder compression test on a school bus diesel, one cylinder reads significantly lower than the others. Adding a small amount of oil through the injector bore raises that cylinder's reading noticeably. This indicates:

A school bus engine has low power and the ECM logs no active fault codes. The technician should:

Blue-gray smoke from the exhaust of a school bus diesel, most noticeable at startup and during deceleration, MOST likely indicates:

A cylinder leakage (leak-down) test on a school bus diesel shows air escaping from the engine oil fill/crankcase. This indicates a leak past the:

A school bus diesel has a steady knock that increases with engine speed and is loudest at light load, with no related fault codes. The technician should suspect:

Technician A says white smoke at cold start that clears as the engine warms can be normal unburned fuel from cold combustion. Technician B says continuous white smoke with a sweet odor and coolant loss indicates coolant entering the combustion chamber. Who is correct?

A school bus engine is consuming engine oil but shows no external leaks and the exhaust shows blue smoke under load. Compression is good. The MOST likely cause is:

Engine oil analysis on a school bus diesel shows elevated coolant (glycol) and a rising sodium/potassium level. This MOST likely indicates:

A school bus diesel cranks slowly and is hard to start on cold mornings only. After warming, it starts normally. The technician should check the:

Which scan tool data set is MOST useful when diagnosing a low-power complaint on a common-rail school bus diesel?

A school bus diesel surges at idle and the rail pressure on the scan tool fluctuates widely. Technician A says a sticking fuel pressure regulator/control valve can cause this. Technician B says a leaking injector or air in the fuel can cause it. Who is correct?

During an engine inspection, the technician finds metallic debris in the engine oil and bearing material in the filter. The BEST next step is to:

A school bus diesel has excessive crankcase pressure (high blow-by) measured at the oil fill. This MOST likely indicates:

A school bus diesel runs rough and misses at idle but smooths out under load. A cylinder cutout test shows little change when one cylinder is disabled. This cylinder is MOST likely:

A coolant odor and white residue are found around a school bus diesel's exhaust outlet, and the surge tank shows combustion bubbles during cranking. The MOST likely cause is:

When road-testing a school bus to verify a low-power complaint, the technician should:

A school bus diesel has a high-pressure fuel leak that sprays atomized fuel near the engine. The technician should:

A school bus diesel will not reach rated power and the scan tool shows the engine is in a derate. Technician A says an emissions-system fault such as a clogged DPF or SCR problem can command a derate. Technician B says low DEF level or quality can also command a derate. Who is correct?

A school bus diesel has a no-start, and the scan tool shows no engine RPM signal during cranking. The MOST likely cause is:

A school bus diesel has fuel in the engine oil (rising oil level, fuel odor). The MOST likely cause is:

Before condemning an electronically controlled diesel engine for a mechanical fault, the technician should FIRST:

A school bus diesel idles roughly and has a knock that disappears when one injector is electronically disabled. This indicates the problem is MOST likely: