Electrical & Electronics — Auto Service Technician (310S) Practice Questions

Free Electrical & Electronics practice questions

1. 1.A parasitic draw test checks for:

   • A.Engine power
   • B.Excessive battery drain when the vehicle is off — should be under 50mA after modules sleep✓
   • C.Charging voltage
   • D.Starter current

   Why: Normal parasitic draw: 20-50mA (modules in sleep mode). Over 50-75mA = something is staying on. Test by measuring current with ammeter in series at the battery.

2. 2.CAN bus communication uses:

   • A.Single wire
   • B.A twisted pair of wires (CAN High and CAN Low) for noise-resistant differential signaling✓
   • C.Fibre optic only
   • D.Wireless only

   Why: CAN uses twisted pair: CAN-H (~3.5V) and CAN-L (~1.5V). The differential signal (difference between them) rejects electrical noise. Open/short in CAN bus affects all modules.

3. 3.Total resistance of two 10Ω resistors in parallel:

   • A.20Ω
   • B.5Ω✓
   • C.10Ω
   • D.100Ω

   Why: Parallel: 1/Rt = 1/R1 + 1/R2 = 1/10 + 1/10 = 2/10. Rt = 10/2 = 5Ω. Equal resistors in parallel: Rt = R ÷ N.

4. 4.The starter motor draws approximately:

   • A.5A
   • B.150-300A during cranking (varies by engine size)✓
   • C.1000A
   • D.10A

   Why: Starter current: 150-250A typical for 4-cylinder, 200-350A for V8. High draw with slow cranking = worn starter, tight engine, or weak battery.

5. 5.The BCM (Body Control Module) manages:

   • A.Engine timing
   • B.Body electrical functions: lights, wipers, locks, windows, and various comfort features✓
   • C.Only the brakes
   • D.Only the engine

   Why: BCM controls body electrical: interior/exterior lights, power windows/locks, wipers, horn, keyless entry. Communicates with other modules via CAN bus.

6. 6.Multiplexing in modern vehicles reduces:

   • A.Vehicle speed
   • B.Wiring by sharing data over communication networks instead of individual wires for each function✓
   • C.Engine power
   • D.Fuel economy

   Why: Instead of 100+ wires from switch to device, a few CAN bus wires carry all data. Modules decode messages and control local devices. Saves weight, cost, and complexity.

7. 7.When programming a new key with a transponder, the process requires:

   • A.Just cutting the key
   • B.A scan tool or manufacturer tool to register the transponder ID with the vehicle's immobilizer module✓
   • C.Only a locksmith
   • D.Only the VIN

   Why: Modern immobilizer systems require the transponder ID to be programmed into the PCM/BCM. Without programming, the key starts nothing — it's an anti-theft measure.

8. 8.Automotive ethernet is being adopted because:

   • A.It's cheaper than CAN
   • B.It provides much higher bandwidth (100 Mbps to 10 Gbps) needed for cameras, ADAS, and infotainment✓
   • C.It's simpler
   • D.It uses less wire

   Why: CAN: 500 Kbps to 1 Mbps. Not enough for cameras (ADAS), high-resolution displays, and large data transfers. Automotive ethernet provides 100 Mbps (100BASE-T1) to 10 Gbps.

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