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100+ Free Automotive Servicing NC III Practice Questions
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2026 Statistics
Key Facts: Automotive Servicing NC III Exam
NC II
Required Prerequisite
TESDA standard
4-6 hours
Total Duration
Written + Practical
₱1,237
Promulgated Fee
TESDA Resolution
5 Core
Diagnostic Areas
Training Regulations
5 years
Certificate Validity
TESDA National Certificate
1 month
Retake Wait Time
For failed units
The TESDA Automotive Servicing NC III assessment in the Philippines is the advanced vocational standard for master auto mechanics. It requires a prior NC II certification. The assessment consists of a written theory exam, oral questioning, and hands-on practical demonstrations across 5 advanced core competencies: electronic engine management (EFI), automatic transmission servicing, mobile air conditioning systems, anti-lock braking systems (ABS), and common rail direct injection (CRDI) diesel systems.
Sample Automotive Servicing NC III Practice Questions
Try these sample questions to test your Automotive Servicing NC III exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.
1While diagnosing a rough idle on a vehicle equipped with an Electronic Fuel Injection (EFI) system, a technician connects an oscilloscope to a magnetic inductive crankshaft position (CKP) sensor. What waveform pattern should be observed on the screen as the engine runs?
A.A continuous digital square wave switching between 0V and 5V
B.An analog sine wave with amplitude and frequency that increase as engine speed increases
C.A constant DC voltage that drops steadily as engine speed increases
D.A pulse-width modulated (PWM) duty-cycle signal that varies between 0V and 12V
Explanation: Magnetic inductive CKP sensors are self-generating sensors that produce an alternating current (AC) voltage signal. The resulting waveform is an analog sine wave where both the voltage amplitude (height of the wave) and frequency (spacing of the cycles) increase directly with the speed of the trigger wheel rotation.
2A vehicle retrieves Diagnostic Trouble Code (DTC) P0171 (System Too Lean - Bank 1). The technician notes that the Short-Term Fuel Trim (STFT) is +18% at idle, but decreases to +2% at 2,500 RPM. What is the most likely cause of this condition?
A.A fuel pump with low volume output or restricted fuel filter
B.A vacuum leak in the intake manifold downstream of the MAF sensor
C.A faulty Mass Air Flow (MAF) sensor reporting high airflow at all speeds
D.One or more fuel injectors stuck open or leaking fuel
Explanation: A vacuum leak allows unmetered air to enter the engine behind the MAF sensor. At idle, this extra air represents a large percentage of the total intake air volume, causing a lean condition and high positive fuel trim. At higher RPM (2,500 RPM), the throttle plate opens, admitting a much larger volume of metered air, which makes the small vacuum leak insignificant and causes fuel trim to return to normal range.
3When measuring the voltage signal of a conventional zirconia oxygen (O2) sensor during closed-loop operation, what voltage range and switching frequency indicate a healthy, fast-acting sensor?
A.A constant 0.5V signal with no deviation
B.Fluctuations between 0.1V and 0.9V at least 8 to 10 times per 10 seconds at 2,000 RPM
C.A linear voltage rise from 1.0V to 5.0V proportional to exhaust temperature
D.A digital signal switching between 0V and 12V at a rate of 50 Hz
Explanation: A healthy zirconia O2 sensor operating in closed-loop mode must rapidly switch back and forth between a lean indicator (under 0.2V) and a rich indicator (above 0.8V) as the PCM adjusts fuel delivery. At 2,000 RPM, a responsive sensor should switch at least 8 to 10 times in a 10-second period; a slower rate indicates a 'lazy' or contaminated sensor.
4An oscilloscope is connected to a fuel injector ground control circuit. While monitoring the waveform, the technician observes that the injector pulse width is 1.8 milliseconds (ms) at normal idle, but increases to 12 ms when the throttle is snapped wide open. What does this change indicate?
A.A faulty PCM injector driver circuit that is failing to control current
B.Normal PCM operation providing enrichment during rapid acceleration
C.A short-circuit to ground in the injector wire harness
D.A high-resistance fault in the injector solenoid coil winding
Explanation: During snap-acceleration, the PCM detects a rapid increase in throttle position and air intake. To maintain engine power and prevent a lean stumble, the PCM switches to an acceleration enrichment mode, extending the ground control time (pulse width) of the fuel injectors to spray more fuel. An increase from 1.8 ms to 12 ms under acceleration is normal operation.
5A technician is testing a three-wire Throttle Position Sensor (TPS). With the ignition switch ON (engine off), the voltmeter connected to the signal wire shows 0.5V at closed throttle and sweep-tests smoothly up to 4.5V at wide-open throttle (WOT). How should the technician evaluate these readings?
A.The sensor is defective because the voltage does not reach a full 5.0V at WOT
B.The sensor is operating normally and is within typical specifications
C.There is a short-circuit to ground on the signal wire causing low voltage at WOT
D.The sensor reference voltage line has excessive resistance
Explanation: Standard three-wire potentiometer TPS sensors do not swing all the way from absolute 0V to 5V. Their normal calibration range is typically 0.5V to 0.7V at idle (throttle closed) and 4.0V to 4.5V at wide-open throttle. A smooth, linear increase in voltage without dropouts during the sweep indicates a fully functional sensor.
6An Engine Coolant Temperature (ECT) sensor has a Negative Temperature Coefficient (NTC). How will the sensor's electrical resistance change as the engine warms up from a cold start to normal operating temperature?
A.The resistance will increase steadily as the temperature rises
B.The resistance will drop significantly as the temperature rises
C.The resistance will remain constant, but its output frequency will change
D.The resistance will fluctuate rapidly between high and low values
Explanation: An NTC thermistor works on the principle that its electrical resistance decreases as temperature increases. When the engine is cold, the ECT sensor resistance is high (typically 10,000+ ohms), and as the engine reaches operating temperature (around 90°C), its resistance drops to a low value (typically 200 to 300 ohms).
7A vehicle equipped with a coil-on-plug (COP) ignition system has a Diagnostic Trouble Code (DTC) P0303 (Cylinder 3 Misfire). Which of the following procedures is the most efficient first step to isolate the fault to either a defective ignition coil or an engine mechanical issue?
A.Replace the fuel injector on cylinder 3 with a new one
B.Swap the ignition coil from cylinder 3 to cylinder 1, clear the codes, and check if the misfire moves to cylinder 1
C.Perform a complete engine compression test on all cylinders
D.Replace the Powertrain Control Module (PCM)
Explanation: Swapping components is a standard, highly efficient diagnostic practice for identifying defective components on multi-cylinder engines. If the ignition coil from cylinder 3 is swapped to cylinder 1 and the DTC changes to P0301 (Cylinder 1 Misfire), it proves the coil is defective. If the misfire remains on cylinder 3, the technician must look at the spark plug, fuel injector, or mechanical compression.
8During diagnostic testing on a Common Rail Direct Injection (CRDI) diesel engine, the engine fails to start. The technician checks common rail pressure using a scan tool and finds it reads 50 bar (725 psi) while cranking. What does this reading indicate?
A.Rail pressure is correct, indicating a electrical injector-trigger fault
B.Rail pressure is too low for the PCM to command injector opening
C.The high-pressure fuel pump is overpressurizing the fuel rail
D.The pressure relief valve on the fuel rail is operating normally
Explanation: Common Rail diesel systems require a high minimum pressure in the rail before the PCM will permit the fuel injectors to pulse. This minimum threshold is typically between 150 and 250 bar (approx. 2,200 to 3,600 psi) depending on system design. A reading of 50 bar is far below the starting threshold, meaning the PCM will disable injector firing to prevent poor fuel atomization.
9A technician is diagnosing an idle speed that remains high (1,200 RPM) after the engine has reached normal operating temperature. Which of the following malfunctions could cause this symptom?
A.An Idle Air Control (IAC) valve stuck in the fully closed position
B.A bypass vacuum leak or an IAC valve stuck open
C.A Throttle Position Sensor (TPS) signal wire shorted to ground
D.A clogged cabin air filter limiting intake airflow
Explanation: Engine idle speed is controlled by regulating the volume of air bypassed around the closed throttle plate. If the IAC valve is stuck in the open position, or if there is an external vacuum leak admitting air downstream of the throttle body, excess air enters the cylinders, causing the PCM to increase fuel and result in a high idle speed.
10A Manifold Absolute Pressure (MAP) sensor is being tested using a digital multimeter and a hand-held vacuum pump. With the key ON, engine off (atmospheric pressure), the sensor outputs 4.5V. As the technician applies 15 inches of mercury (in. Hg) vacuum, what should happen to the voltage signal if the sensor is working properly?
A.The voltage signal should increase toward 5.0V
B.The voltage signal should decrease significantly (typically to around 1.5V to 2.0V)
C.The voltage signal should convert into a frequency signal switching at 50 Hz
D.The voltage signal should drop to exactly 0V and set a DTC
Explanation: A MAP sensor measures absolute pressure inside the intake manifold. At atmospheric pressure (high pressure), its output voltage is high (around 4.5V). When vacuum is applied (lower absolute pressure), the output voltage drops accordingly. Applying 15 in. Hg of vacuum should drop the voltage signal down to a range of 1.5V to 2.0V depending on sensor specifications.
About the Automotive Servicing NC III Practice Questions
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