Postal Exam 943/944/945 Study Guide USPS EXAM
USPS 943/944/945 PRACTICE EXAM — COMPLETE 40 QUESTIONS
1. A vehicle with a fully charged 12-volt battery cranks slowly. The starter
amperage draw is 350 amps (spec is 150-200 amps). Voltage at the starter while
cranking is 9.2 volts. What is the most likely cause?
• A) Weak battery
• B) High resistance in the positive battery cable
• C) Shorted starter armature
• D) Engine mechanical binding
Answer: C — A shorted armature creates excessive current draw (350A vs 150-
200A spec) while dropping system voltage. A weak battery would show low
voltage even before cranking. High cable resistance would reduce current, not
increase it.
2. A disc brake rotor has a deep blue coloration and hard spots on the friction
surface. This condition is most directly caused by:
• A) Glazed brake pads
• B) Excessive lateral runout
• C) Repeated heavy braking without cool-down
• D) A stuck caliper slide pin
Answer: C — Severe heat cycles from repeated heavy braking cause the rotor
material to crystallize into hard spots and turn blue. Glazed pads affect friction but
don't discolor rotors. Runout causes pedal pulsation, not coloration.
,3. On a port fuel-injected engine, fuel pressure is 10 psi below specification at
idle. When the vacuum hose is removed from the fuel pressure regulator, the
pressure rises to specification. This indicates:
• A) A restricted fuel return line
• B) A weak fuel pump
• C) A ruptured regulator diaphragm
• D) The regulator is operating correctly
Answer: D — Removing vacuum raises regulator pressure by about 8-10 psi
because manifold vacuum normally lowers pressure at idle. If pressure returns to
spec with vacuum removed, the regulator is functioning properly and the base
pressure is correct.
4. A scan tool shows an O2 sensor voltage stuck at 0.45 volts on a warmed-up
engine in closed loop. The most likely cause is:
• A) An exhaust leak before the sensor
• B) A rich fuel mixture
• C) An open circuit in the O2 sensor signal wire
• D) A vacuum leak
Answer: C — 0.45 volts is the bias voltage generated by the PCM when the O2
sensor circuit is open or unresponsive. A rich mixture would read above 0.8V. A
vacuum leak would show lean (below 0.2V).
5. A vacuum gauge connected to the intake manifold reads a steady 15 inHg at
idle (normal is 18-22 inHg). When the throttle is snapped open, the gauge drops
to 2 inHg and then returns to 15 inHg. This indicates:
• A) A restricted exhaust system
, • B) Late ignition timing
• C) Weak valve springs
• D) Normal operation for a worn engine
Answer: C — Weak valve springs allow the gauge to drop abnormally low (2 inHg)
on snap-throttle due to valve float, and the return to idle is slow or incomplete. A
restricted exhaust would show a gradual vacuum drop at steady RPM.
6. The vibration damper (harmonic balancer) on an automotive engine is
mounted to the:
• A) Camshaft
• B) Flywheel
• C) Crankshaft
• D) Transmission input shaft
Answer: C — The harmonic balancer is bolted to the front of the crankshaft to
absorb torsional vibrations. The camshaft uses a timing gear/sprocket. The
flywheel is at the rear of the crank.
7. A customer complains that the ABS light comes on only when driving over
rough roads. The most likely cause is:
• A) A faulty ABS control module
• B) Low brake fluid level
• C) An intermittent wheel speed sensor wiring issue
• D) A stuck proportioning valve
Answer: C — Rough roads cause sensor wires to bounce and momentarily lose
connection. A faulty module or low fluid would set the light constantly or under
braking, not specifically on rough roads.
USPS 943/944/945 PRACTICE EXAM — COMPLETE 40 QUESTIONS
1. A vehicle with a fully charged 12-volt battery cranks slowly. The starter
amperage draw is 350 amps (spec is 150-200 amps). Voltage at the starter while
cranking is 9.2 volts. What is the most likely cause?
• A) Weak battery
• B) High resistance in the positive battery cable
• C) Shorted starter armature
• D) Engine mechanical binding
Answer: C — A shorted armature creates excessive current draw (350A vs 150-
200A spec) while dropping system voltage. A weak battery would show low
voltage even before cranking. High cable resistance would reduce current, not
increase it.
2. A disc brake rotor has a deep blue coloration and hard spots on the friction
surface. This condition is most directly caused by:
• A) Glazed brake pads
• B) Excessive lateral runout
• C) Repeated heavy braking without cool-down
• D) A stuck caliper slide pin
Answer: C — Severe heat cycles from repeated heavy braking cause the rotor
material to crystallize into hard spots and turn blue. Glazed pads affect friction but
don't discolor rotors. Runout causes pedal pulsation, not coloration.
,3. On a port fuel-injected engine, fuel pressure is 10 psi below specification at
idle. When the vacuum hose is removed from the fuel pressure regulator, the
pressure rises to specification. This indicates:
• A) A restricted fuel return line
• B) A weak fuel pump
• C) A ruptured regulator diaphragm
• D) The regulator is operating correctly
Answer: D — Removing vacuum raises regulator pressure by about 8-10 psi
because manifold vacuum normally lowers pressure at idle. If pressure returns to
spec with vacuum removed, the regulator is functioning properly and the base
pressure is correct.
4. A scan tool shows an O2 sensor voltage stuck at 0.45 volts on a warmed-up
engine in closed loop. The most likely cause is:
• A) An exhaust leak before the sensor
• B) A rich fuel mixture
• C) An open circuit in the O2 sensor signal wire
• D) A vacuum leak
Answer: C — 0.45 volts is the bias voltage generated by the PCM when the O2
sensor circuit is open or unresponsive. A rich mixture would read above 0.8V. A
vacuum leak would show lean (below 0.2V).
5. A vacuum gauge connected to the intake manifold reads a steady 15 inHg at
idle (normal is 18-22 inHg). When the throttle is snapped open, the gauge drops
to 2 inHg and then returns to 15 inHg. This indicates:
• A) A restricted exhaust system
, • B) Late ignition timing
• C) Weak valve springs
• D) Normal operation for a worn engine
Answer: C — Weak valve springs allow the gauge to drop abnormally low (2 inHg)
on snap-throttle due to valve float, and the return to idle is slow or incomplete. A
restricted exhaust would show a gradual vacuum drop at steady RPM.
6. The vibration damper (harmonic balancer) on an automotive engine is
mounted to the:
• A) Camshaft
• B) Flywheel
• C) Crankshaft
• D) Transmission input shaft
Answer: C — The harmonic balancer is bolted to the front of the crankshaft to
absorb torsional vibrations. The camshaft uses a timing gear/sprocket. The
flywheel is at the rear of the crank.
7. A customer complains that the ABS light comes on only when driving over
rough roads. The most likely cause is:
• A) A faulty ABS control module
• B) Low brake fluid level
• C) An intermittent wheel speed sensor wiring issue
• D) A stuck proportioning valve
Answer: C — Rough roads cause sensor wires to bounce and momentarily lose
connection. A faulty module or low fluid would set the light constantly or under
braking, not specifically on rough roads.
