Automobile Electrical and Electronic Systems
This domain tests the battery, charging, starting, ignition, lighting, fuses, basic circuit calculations and electronic control systems.
Battery and circuits
- A 12 V lead-acid battery has six cells, each about 2.1 V, giving about 12.6 V at rest.
- The alternator charges the battery; the starter motor cranks the engine.
- Ohm's law: V = I × R. Power: P = V × I.
- Fuses protect circuits by melting when current is excessive.
- Series connection adds voltages; parallel connection adds capacities while voltage stays the same.
Electronics
- Sensors feed the engine control unit (ECU), which controls injection and ignition.
- A multimeter measures voltage, current and resistance; an ammeter is connected in series.
- CAN bus reduces wiring by letting control units share data.
- Never disconnect the battery while the engine is running; the alternator can be damaged.
Worked example
Two 12 V, 60 Ah batteries are connected in parallel. Voltage stays 12 V and capacity adds: 12 V, 120 Ah. If the same batteries are connected in series, voltage adds to 24 V but capacity stays 60 Ah. The reasoning is that parallel branches share current, while series cells push the same current through a higher voltage.
Traps
- Connecting an ammeter in parallel, which can blow its fuse.
- Assuming a 12 V battery reads exactly 12.0 V when healthy; about 12.6 V is normal.
- Treating series and parallel rules as interchangeable.
- Replacing a blown fuse with a higher-rated one instead of finding the fault.