Auto Electricals flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Ohm's law
- The relationship V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms; used to calculate any one value when the other two are known.
- Series circuit
- A circuit with only one path for current; total resistance is the sum of individual resistances, current is the same throughout, and voltage drops add to the source voltage.
- Parallel circuit
- A circuit with multiple current paths; voltage is the same across each branch, total resistance is less than the smallest branch resistance, and branch currents sum to total current.
- Kirchhoff's voltage law
- The algebraic sum of all voltages around any closed loop in a circuit equals zero; used to analyze complex circuits and verify voltage drops.
- Voltage drop
- The loss of voltage across a resistance in a circuit, calculated as V = I × R; excessive drop in conductors causes dim lights and slow motors.
- Lead-acid cell voltage
- A fully charged lead-acid cell produces approximately 2.1 V; a 12 V battery has six cells in series, giving about 12.6 V at rest.
- Cold cranking amps
- The current a battery can deliver for 30 seconds at −18°C while maintaining at least 7.2 V; indicates starting capability in cold weather.
- Alternator AC ripple
- Alternating current superimposed on the DC output; measured with a multimeter set to AC volts; more than 0.5 V AC suggests failed rectifier diodes.
- Parasitic draw
- Current drawn by the vehicle when all modules are asleep; typically under 50 mA after 20–40 minutes; higher values indicate a fault causing battery drain.
- Starter voltage drop
- The voltage lost across cables and connections during cranking; maximum acceptable is 0.5 V on the positive side and 0.3 V on the ground side.
- Halogen bulb handling
- Never touch the glass envelope of a halogen bulb with bare fingers; skin oils create hot spots that cause premature bulb failure.
- LED turn signal hyper-flash
- Rapid flashing caused by lower current draw of LED bulbs; the vehicle's flasher or body control module detects the reduced load as a bulb failure.
- Brake light switch
- A normally open switch that closes when the brake pedal is pressed; supplies power to brake lights and signals the ECM for shift interlock and cruise control.
- Trailer 4-pin wiring
- Standard colors: white = ground, brown = tail/running lights, yellow = left turn/brake, green = right turn/brake; used on light-duty trailers.
- Fuse rating rule
- Continuous load should not exceed 80% of the fuse rating; the fuse must protect the smallest wire in the circuit from overheating.
- ISO relay terminals
- Standard numbering: 30 = battery positive, 87 = load output normally open, 86 = coil positive, 85 = coil ground, 87a = load output normally closed.
- Voltage drop testing
- Measuring voltage across a connection while the circuit is under load; more than 0.1 V per connection indicates excessive resistance; preferred over resistance testing for high-current circuits.
- Wire gauge AWG
- American Wire Gauge; smaller numbers indicate larger conductors; 18 AWG is typical for low-current signal circuits, 10–12 AWG for high-current accessories.
- CAN bus voltage
- Differential pair; CAN High and CAN Low each rest at about 2.5 V; during a dominant bit CAN High rises to ~3.5 V and CAN Low falls to ~1.5 V.
- CAN termination resistance
- Two 120 Ω resistors at each end of the bus; measured across CAN High and CAN Low with power off, the reading should be approximately 60 Ω.
- LIN bus
- Single-wire, low-speed (9.6–19.2 kbps) master-slave network; dominant state is 12 V, recessive is 0 V; used for body and convenience devices.
- 5 V reference circuit
- Regulated 5 V supply from the ECM to sensors; a short to ground or voltage affects all sensors sharing that reference, causing multiple codes.
- Hall effect sensor
- A sensor that produces a digital square wave when a magnetic field is interrupted; commonly used for crankshaft and camshaft position sensing.
- DMM input impedance
- Typically 10 MΩ for a digital multimeter; high impedance prevents the meter from loading the circuit and giving inaccurate voltage readings.
- Oscilloscope time base
- The horizontal scale setting in seconds per division; adjust to display at least two complete cycles of the signal being tested.
- Fuel injector waveform
- A current ramp followed by an inductive kick of 60–100 V at turn-off; a missing kick indicates an open injector coil.
- Freeze-frame data
- Scan tool snapshot of sensor values and operating conditions at the moment a diagnostic trouble code was set; useful for intermittent faults.
- Bidirectional scan tool
- A scan tool feature that commands modules to actuate relays, injectors, or motors; allows circuit testing without disassembly.
- Short to ground
- An unintended path from a circuit to ground; typically blows a fuse; isolate by disconnecting components and measuring resistance to ground.
- High resistance fault
- Corroded or loose connection that limits current; causes dim lights, slow motors, and heat; detected by voltage drop testing under load.
- Intermittent fault diagnosis
- Use wiggle tests, freeze-frame data, and event recording; check for chafed harnesses, loose grounds, and connector terminal tension.
- High-voltage safety
- Orange cables indicate high voltage on hybrid and electric vehicles; only qualified personnel should service; use insulated tools rated 1000 V and follow lockout/tagout.