USPS 943 AUTOMOTIVE TECHNICIAN EXAMINATION
COMPLETE QUESTIONS AND DETAILED SOLUTIONS
LATEST UPDATE THIS YEAR JUST RELEASED
Exam Coverage Summary
1. Engine Operation and Diagnostics — Four-stroke cycles, compression, vacuum readings,
cylinder leakage, valve timing, lubrication, and cooling systems.
2. Fuel and Air Induction Systems — Fuel delivery, carburetion principles, fuel injection, air-fuel
ratios, intake systems, and throttle operation.
3. Ignition Systems — Spark plugs, ignition timing, distributors, coils, electronic ignition, firing
order, and ignition troubleshooting.
4. Emission Control Systems — PCV, EGR, catalytic converters, oxygen sensors, evaporative
controls, and exhaust-gas analysis.
5. Electrical and Starting/Charging Systems — Batteries, alternators, starters, voltage, current,
resistance, circuits, and electrical diagnosis.
6. Brake Systems — Hydraulic brakes, drum and disc brakes, master cylinders, wheel cylinders,
calipers, boosters, and ABS fundamentals.
7. Steering, Suspension, and Alignment — Ball joints, tie rods, steering linkage, shocks, springs,
caster, camber, toe, and wheel alignment.
8. Transmission and Drivetrain — Manual and automatic transmissions, clutches, planetary gears,
differentials, driveshafts, axles, and universal joints.
9. Preventive Maintenance and Troubleshooting — Systematic diagnosis, inspection procedures,
lubrication, fluid service, belt and hose inspection, and symptom analysis.
10. Automotive Safety and Workshop Practices — Lifting vehicles, jack stands, battery safety,
hazardous fluids, tool selection, PPE, and safe repair procedures.
1. During a compression test, a cylinder initially records low compression that
increases significantly after adding a small amount of oil into the cylinder. What does
this result most strongly indicate?
A. A burnt exhaust valve
B. Worn piston rings or cylinder walls
C. A defective rocker arm
D. An improperly adjusted distributor
,Answer: B. Worn piston rings or cylinder walls
Rationale: Oil temporarily seals the gap between worn rings and cylinder walls. If
compression rises substantially, the leakage is likely occurring past the piston rings
rather than through the valves.
2. When a properly tuned gasoline engine is idling at operating temperature, which
vacuum gauge reading and needle behavior would normally indicate good engine
condition?
A. A steady reading approximately between 14 and 22 inches of mercury
B. A steady reading approximately between 2 and 5 inches of mercury
C. A rapidly fluctuating reading between 0 and 10 inches of mercury
D. A constant reading above 30 inches of mercury
Answer: A. A steady reading approximately between 14 and 22 inches of mercury
Rationale: A healthy engine at idle commonly produces a relatively steady manifold
vacuum in this general range, although altitude and engine design affect the exact
reading.
3. During a cylinder leakage test, air is heard escaping through the radiator neck while
the tested cylinder is pressurized. Which condition should the technician suspect first?
A. Worn piston rings
B. A leaking exhaust valve
C. A defective head gasket or cracked cylinder head
D. A restricted air filter
Answer: C. A defective head gasket or cracked cylinder head
Rationale: Air entering the cooling system during a leak-down test indicates a
combustion chamber-to-coolant passage leak, commonly caused by a failed head gasket
or cracked head.
,4. In a conventional four-stroke gasoline engine, during which stroke does the piston
move downward while the intake valve is open and the air-fuel mixture enters the
cylinder?
A. Compression stroke
B. Power stroke
C. Exhaust stroke
D. Intake stroke
Answer: D. Intake stroke
Rationale: During the intake stroke, the piston travels downward with the intake valve
open, creating a pressure difference that draws the mixture into the cylinder.
5. How many complete revolutions does the crankshaft make while the camshaft
completes one full revolution in a conventional four-stroke engine?
A. One-quarter revolution
B. One-half revolution
C. Two revolutions
D. Four revolutions
Answer: C. Two revolutions
Rationale: The four-stroke cycle requires two crankshaft revolutions, while the camshaft
rotates once to operate the valves through the complete cycle.
6. What is the primary function of the engine lubrication system in a conventional
internal combustion engine?
A. To increase fuel pressure
B. To reduce friction and remove heat from moving components
C. To increase exhaust backpressure
D. To control ignition timing
Answer: B. To reduce friction and remove heat from moving components
, Rationale: Engine oil lubricates moving parts, reduces friction and wear, helps carry
heat away, and suspends contaminants for removal by the filter.
7. If an engine overheats primarily while idling but operates at normal temperature
when traveling at highway speed, which problem should be investigated first?
A. A defective radiator fan or fan control system
B. An excessively rich fuel mixture
C. A worn clutch disc
D. A defective transmission modulator
Answer: A. A defective radiator fan or fan control system
Rationale: At highway speed, airflow through the radiator may be sufficient even
without the fan. At idle, proper fan operation is essential for adequate cooling airflow.
8. What is the primary purpose of a thermostat in a liquid-cooled automotive engine?
A. To maintain the engine within its designed operating temperature range
B. To increase fuel pressure during acceleration
C. To regulate transmission fluid temperature
D. To control battery charging voltage
Answer: A. To maintain the engine within its designed operating temperature range
Rationale: The thermostat regulates coolant flow to help the engine warm up quickly
and maintain an appropriate operating temperature.
9. A vehicle's engine develops excessive white exhaust smoke accompanied by
unexplained coolant loss. Which condition is most likely responsible?
A. A restricted fuel filter
B. Coolant entering the combustion chamber
C. A weak alternator
D. A slipping transmission
COMPLETE QUESTIONS AND DETAILED SOLUTIONS
LATEST UPDATE THIS YEAR JUST RELEASED
Exam Coverage Summary
1. Engine Operation and Diagnostics — Four-stroke cycles, compression, vacuum readings,
cylinder leakage, valve timing, lubrication, and cooling systems.
2. Fuel and Air Induction Systems — Fuel delivery, carburetion principles, fuel injection, air-fuel
ratios, intake systems, and throttle operation.
3. Ignition Systems — Spark plugs, ignition timing, distributors, coils, electronic ignition, firing
order, and ignition troubleshooting.
4. Emission Control Systems — PCV, EGR, catalytic converters, oxygen sensors, evaporative
controls, and exhaust-gas analysis.
5. Electrical and Starting/Charging Systems — Batteries, alternators, starters, voltage, current,
resistance, circuits, and electrical diagnosis.
6. Brake Systems — Hydraulic brakes, drum and disc brakes, master cylinders, wheel cylinders,
calipers, boosters, and ABS fundamentals.
7. Steering, Suspension, and Alignment — Ball joints, tie rods, steering linkage, shocks, springs,
caster, camber, toe, and wheel alignment.
8. Transmission and Drivetrain — Manual and automatic transmissions, clutches, planetary gears,
differentials, driveshafts, axles, and universal joints.
9. Preventive Maintenance and Troubleshooting — Systematic diagnosis, inspection procedures,
lubrication, fluid service, belt and hose inspection, and symptom analysis.
10. Automotive Safety and Workshop Practices — Lifting vehicles, jack stands, battery safety,
hazardous fluids, tool selection, PPE, and safe repair procedures.
1. During a compression test, a cylinder initially records low compression that
increases significantly after adding a small amount of oil into the cylinder. What does
this result most strongly indicate?
A. A burnt exhaust valve
B. Worn piston rings or cylinder walls
C. A defective rocker arm
D. An improperly adjusted distributor
,Answer: B. Worn piston rings or cylinder walls
Rationale: Oil temporarily seals the gap between worn rings and cylinder walls. If
compression rises substantially, the leakage is likely occurring past the piston rings
rather than through the valves.
2. When a properly tuned gasoline engine is idling at operating temperature, which
vacuum gauge reading and needle behavior would normally indicate good engine
condition?
A. A steady reading approximately between 14 and 22 inches of mercury
B. A steady reading approximately between 2 and 5 inches of mercury
C. A rapidly fluctuating reading between 0 and 10 inches of mercury
D. A constant reading above 30 inches of mercury
Answer: A. A steady reading approximately between 14 and 22 inches of mercury
Rationale: A healthy engine at idle commonly produces a relatively steady manifold
vacuum in this general range, although altitude and engine design affect the exact
reading.
3. During a cylinder leakage test, air is heard escaping through the radiator neck while
the tested cylinder is pressurized. Which condition should the technician suspect first?
A. Worn piston rings
B. A leaking exhaust valve
C. A defective head gasket or cracked cylinder head
D. A restricted air filter
Answer: C. A defective head gasket or cracked cylinder head
Rationale: Air entering the cooling system during a leak-down test indicates a
combustion chamber-to-coolant passage leak, commonly caused by a failed head gasket
or cracked head.
,4. In a conventional four-stroke gasoline engine, during which stroke does the piston
move downward while the intake valve is open and the air-fuel mixture enters the
cylinder?
A. Compression stroke
B. Power stroke
C. Exhaust stroke
D. Intake stroke
Answer: D. Intake stroke
Rationale: During the intake stroke, the piston travels downward with the intake valve
open, creating a pressure difference that draws the mixture into the cylinder.
5. How many complete revolutions does the crankshaft make while the camshaft
completes one full revolution in a conventional four-stroke engine?
A. One-quarter revolution
B. One-half revolution
C. Two revolutions
D. Four revolutions
Answer: C. Two revolutions
Rationale: The four-stroke cycle requires two crankshaft revolutions, while the camshaft
rotates once to operate the valves through the complete cycle.
6. What is the primary function of the engine lubrication system in a conventional
internal combustion engine?
A. To increase fuel pressure
B. To reduce friction and remove heat from moving components
C. To increase exhaust backpressure
D. To control ignition timing
Answer: B. To reduce friction and remove heat from moving components
, Rationale: Engine oil lubricates moving parts, reduces friction and wear, helps carry
heat away, and suspends contaminants for removal by the filter.
7. If an engine overheats primarily while idling but operates at normal temperature
when traveling at highway speed, which problem should be investigated first?
A. A defective radiator fan or fan control system
B. An excessively rich fuel mixture
C. A worn clutch disc
D. A defective transmission modulator
Answer: A. A defective radiator fan or fan control system
Rationale: At highway speed, airflow through the radiator may be sufficient even
without the fan. At idle, proper fan operation is essential for adequate cooling airflow.
8. What is the primary purpose of a thermostat in a liquid-cooled automotive engine?
A. To maintain the engine within its designed operating temperature range
B. To increase fuel pressure during acceleration
C. To regulate transmission fluid temperature
D. To control battery charging voltage
Answer: A. To maintain the engine within its designed operating temperature range
Rationale: The thermostat regulates coolant flow to help the engine warm up quickly
and maintain an appropriate operating temperature.
9. A vehicle's engine develops excessive white exhaust smoke accompanied by
unexplained coolant loss. Which condition is most likely responsible?
A. A restricted fuel filter
B. Coolant entering the combustion chamber
C. A weak alternator
D. A slipping transmission
