Automotive Electrical and Electronic Systems
Domain focus
Automotive Electrical and Electronic Systems tests basic circuit laws, battery, starting, charging, lighting, fuses, relays, sensors, and ECU inputs. Expect diagnosis rather than only component names.
Core rules
- Ohm's law: V = I × R. Power: P = V × I. In series, current is common and voltages add; in parallel, voltage is common and currents add.
- The battery stores chemical energy; the starter converts electrical energy to mechanical energy; the alternator charges during running. Fuses protect circuits from excess current.
- Measure voltage in parallel and current in series. A relay uses a small control current to switch a larger load current.
- Sensors supply ECU inputs; actuators carry out ECU commands. Poor grounds cause dim lights and strange faults.
Worked example
A 12 V bulb rated 24 W draws I = P/V = 24/12 = 2 A. Its resistance is R = V/I = 12/2 = 6 Ω. If two such 6 Ω bulbs are in series on 12 V, total resistance is 12 Ω, current is 1 A, and each bulb is dimmer because it receives less voltage.
Traps
Measuring current across a battery, fitting a higher-rated fuse, leaving the ignition on, and assuming a dead battery is the only no-crank cause are common errors.