NYC DCAS AUTO MECHANIC EXAM: COMPREHENSIVE QUESTIONS AND ANSWERS | LATEST
UPDATE
Core Domains
1. Diesel Engine Fundamentals and Operation
2. Fuel Injection, Air Intake, and Emission Control Systems
3. Electrical and Electronic Systems
4. Braking Systems (Air and Hydraulic)
5. Steering, Suspension, and Drivetrain
6. Preventive Maintenance, Diagnostics, and Safety Standards
Introduction
This comprehensive assessment is designed to evaluate the knowledge and skills required for the
New York City Department of Citywide Administrative Services Auto Mechanic civil service
examination. The examination assesses technical proficiency in diesel and gasoline engine
systems, diagnostic reasoning, information ordering, and mathematical reasoning essential for
municipal fleet maintenance. Candidates will demonstrate competency across multiple domains,
including engine overhaul, fuel injection, electrical troubleshooting, brake systems, and workplace
safety. Each question emphasizes real-world application and critical decision-making in the
inspection, diagnosis, repair, and maintenance of City of New York vehicles and equipment.
Successful completion indicates readiness for the responsibilities of a municipal auto mechanic.
SECTION ONE: QUESTIONS 1–100
Question 1
A diesel engine relies on which principle for ignition?
A. Spark ignition
B. Compression ignition
C. Electrical ignition
D. Vacuum ignition
🟢 B. Compression ignition
,🔴 RATIONALE: Diesel engines ignite fuel using the heat generated by high compression of air
in the cylinder, rather than spark plugs. The air is compressed to a ratio of 14:1 to 25:1, raising
its temperature above the autoignition point of diesel fuel.
Question 2
What are the four strokes of a four-stroke diesel engine in correct order?
A. Intake, compression, power, exhaust
B. Intake, power, compression, exhaust
C. Compression, intake, power, exhaust
D. Intake, exhaust, compression, power
🟢 A. Intake, compression, power, exhaust
🔴 RATIONALE: In a four-stroke diesel engine, the piston moves down for intake of air, up for
compression, down during the power stroke after fuel injection ignites, and up for exhaust.
Question 3
During the compression stroke of a diesel engine, what occurs?
A. Air and fuel mixture is compressed and ignited by a spark plug
B. Only air is compressed, raising its temperature above the autoignition point of diesel fuel
C. Exhaust gases are forced out through the open exhaust valve
D. The intake valve opens to allow fresh air into the cylinder
🟢 B. Only air is compressed, raising its temperature above the autoignition point of diesel fuel
🔴 RATIONALE: Diesel engines compress air alone to high pressures, creating extreme
temperatures; diesel fuel is then injected and ignites spontaneously due to the heat, with no
spark plug.
Question 4
The crankshaft converts the reciprocating motion of the pistons into what type of motion?
A. Oscillating motion
B. Rotary motion
,C. Linear thrust
D. Hydraulic pressure
🟢 B. Rotary motion
🔴 RATIONALE: The crankshaft transforms the up-and-down motion of the pistons into
rotational motion to drive the transmission and accessories.
Question 5
A camshaft in a diesel engine is responsible for:
A. Driving the oil pump
B. Opening and closing the intake and exhaust valves
C. Converting linear motion to rotary motion
D. Regulating fuel pressure at the injectors
🟢 B. Opening and closing the intake and exhaust valves
🔴 RATIONALE: The camshaft controls valve timing by opening and closing the intake and
exhaust valves at the correct intervals during the four-stroke cycle.
Question 6
What is the primary purpose of engine oil?
A. Increase fuel pressure
B. Lubricate moving components and reduce friction
C. Cool the passenger compartment
D. Increase battery voltage
🟢 B. Lubricate moving components and reduce friction
🔴 RATIONALE: Engine oil lubricates moving parts, reduces friction and wear, helps carry heat
away, and suspends contaminants for removal by the oil filter.
Question 7
What does the viscosity rating of engine oil describe?
, A. Its electrical resistance
B. Its resistance to flow
C. Its freezing point only
D. Its detergent concentration
🟢 B. Its resistance to flow
🔴 RATIONALE: Viscosity describes a fluid's resistance to flow. Multi-grade oils are formulated
to provide suitable viscosity over a range of temperatures.
Question 8
What is the function of an oil filter?
A. Remove contaminants from engine oil
B. Increase oil temperature
C. Regulate coolant pressure
D. Filter fuel from the tank
🟢 A. Remove contaminants from engine oil
🔴 RATIONALE: The oil filter removes suspended contaminants from engine oil before the oil
circulates through engine components.
Question 9
What is the most common cause of low engine oil pressure?
A. Excessive tire pressure
B. Low oil level or excessive bearing clearance
C. A fully charged battery
D. A clean air filter
🟢 B. Low oil level or excessive bearing clearance
🔴 RATIONALE: Low oil level reduces available oil, while excessive bearing clearance can allow
oil pressure to escape too readily.
Question 10
What is the purpose of engine coolant?
UPDATE
Core Domains
1. Diesel Engine Fundamentals and Operation
2. Fuel Injection, Air Intake, and Emission Control Systems
3. Electrical and Electronic Systems
4. Braking Systems (Air and Hydraulic)
5. Steering, Suspension, and Drivetrain
6. Preventive Maintenance, Diagnostics, and Safety Standards
Introduction
This comprehensive assessment is designed to evaluate the knowledge and skills required for the
New York City Department of Citywide Administrative Services Auto Mechanic civil service
examination. The examination assesses technical proficiency in diesel and gasoline engine
systems, diagnostic reasoning, information ordering, and mathematical reasoning essential for
municipal fleet maintenance. Candidates will demonstrate competency across multiple domains,
including engine overhaul, fuel injection, electrical troubleshooting, brake systems, and workplace
safety. Each question emphasizes real-world application and critical decision-making in the
inspection, diagnosis, repair, and maintenance of City of New York vehicles and equipment.
Successful completion indicates readiness for the responsibilities of a municipal auto mechanic.
SECTION ONE: QUESTIONS 1–100
Question 1
A diesel engine relies on which principle for ignition?
A. Spark ignition
B. Compression ignition
C. Electrical ignition
D. Vacuum ignition
🟢 B. Compression ignition
,🔴 RATIONALE: Diesel engines ignite fuel using the heat generated by high compression of air
in the cylinder, rather than spark plugs. The air is compressed to a ratio of 14:1 to 25:1, raising
its temperature above the autoignition point of diesel fuel.
Question 2
What are the four strokes of a four-stroke diesel engine in correct order?
A. Intake, compression, power, exhaust
B. Intake, power, compression, exhaust
C. Compression, intake, power, exhaust
D. Intake, exhaust, compression, power
🟢 A. Intake, compression, power, exhaust
🔴 RATIONALE: In a four-stroke diesel engine, the piston moves down for intake of air, up for
compression, down during the power stroke after fuel injection ignites, and up for exhaust.
Question 3
During the compression stroke of a diesel engine, what occurs?
A. Air and fuel mixture is compressed and ignited by a spark plug
B. Only air is compressed, raising its temperature above the autoignition point of diesel fuel
C. Exhaust gases are forced out through the open exhaust valve
D. The intake valve opens to allow fresh air into the cylinder
🟢 B. Only air is compressed, raising its temperature above the autoignition point of diesel fuel
🔴 RATIONALE: Diesel engines compress air alone to high pressures, creating extreme
temperatures; diesel fuel is then injected and ignites spontaneously due to the heat, with no
spark plug.
Question 4
The crankshaft converts the reciprocating motion of the pistons into what type of motion?
A. Oscillating motion
B. Rotary motion
,C. Linear thrust
D. Hydraulic pressure
🟢 B. Rotary motion
🔴 RATIONALE: The crankshaft transforms the up-and-down motion of the pistons into
rotational motion to drive the transmission and accessories.
Question 5
A camshaft in a diesel engine is responsible for:
A. Driving the oil pump
B. Opening and closing the intake and exhaust valves
C. Converting linear motion to rotary motion
D. Regulating fuel pressure at the injectors
🟢 B. Opening and closing the intake and exhaust valves
🔴 RATIONALE: The camshaft controls valve timing by opening and closing the intake and
exhaust valves at the correct intervals during the four-stroke cycle.
Question 6
What is the primary purpose of engine oil?
A. Increase fuel pressure
B. Lubricate moving components and reduce friction
C. Cool the passenger compartment
D. Increase battery voltage
🟢 B. Lubricate moving components and reduce friction
🔴 RATIONALE: Engine oil lubricates moving parts, reduces friction and wear, helps carry heat
away, and suspends contaminants for removal by the oil filter.
Question 7
What does the viscosity rating of engine oil describe?
, A. Its electrical resistance
B. Its resistance to flow
C. Its freezing point only
D. Its detergent concentration
🟢 B. Its resistance to flow
🔴 RATIONALE: Viscosity describes a fluid's resistance to flow. Multi-grade oils are formulated
to provide suitable viscosity over a range of temperatures.
Question 8
What is the function of an oil filter?
A. Remove contaminants from engine oil
B. Increase oil temperature
C. Regulate coolant pressure
D. Filter fuel from the tank
🟢 A. Remove contaminants from engine oil
🔴 RATIONALE: The oil filter removes suspended contaminants from engine oil before the oil
circulates through engine components.
Question 9
What is the most common cause of low engine oil pressure?
A. Excessive tire pressure
B. Low oil level or excessive bearing clearance
C. A fully charged battery
D. A clean air filter
🟢 B. Low oil level or excessive bearing clearance
🔴 RATIONALE: Low oil level reduces available oil, while excessive bearing clearance can allow
oil pressure to escape too readily.
Question 10
What is the purpose of engine coolant?
