Build a sensor-to-ECU-to-actuator system, discover how diodes and transistor drivers cooperate, then diagnose faults from actual simulated evidence. This is a teaching model of a 12 V cooling-fan relay system—not a vehicle-specific wiring diagram.
Choose a lesson to read its key concept and automotive example. Complete all 10 to earn the first milestone.
All wiring, readings, and waveforms here are simulated. Never probe a live airbag, high-voltage, or unknown control circuit based on a teaching diagram. On real vehicles, consult OEM service information, observe safe back-probing practices, and use the specified load, circuit protection, and test method.
Match six device descriptions to their jobs. Check answers to reveal explanations; score 5/6 or better to complete this station.
This model uses an N-channel MOSFET as a low-side driver for a relay coil; the relay contacts separately switch the fan motor. Assign the correct device to each position.
Change engine temperature, A/C request, and the 5 V sensor reference. The ECU uses the sensor voltage to estimate temperature, then commands the fan relay when temperature is ≥ 95°C or A/C is requested. For simplicity, the model uses a linear 0.5–4.5 V temperature signal over 0–120°C; real sensors and controls vary.
Relay coil: 80 Ω; fan load: conceptual 6 A when relay closes. A healthy MOSFET is modeled as an ideal switch. A shorted drain–source can energize the coil even when the ECU commands OFF.
When the 5 V reference is absent, the sensor reading is invalid and the ECU's output is deliberately shown as undetermined/fail-safe policy dependent, rather than pretending every vehicle behaves identically.
Diode flyback protection is connected across the relay coil with the cathode toward the positive supply; it is normally reverse-biased and conducts transient current when the coil is switched off.
For each case, compare the command, coil voltage, drain voltage, relay behavior, and fan outcome. Choose the best supported next conclusion. All listed measurements are simulated; no diagnosis is based on a single voltage alone.
Answer 8 questions. Pass mark: 7/8. Your badge unlocks after the five lab milestones and a passing exam.