Your FREE ASE A6 Flashcards 2026 – 200+ Cards

The electrical pressure (potential difference) that pushes current through a circuit, measured in volts. In Ohm's law, V = I × R.

The flow of electric charge through a circuit, measured in amperes (amps). In Ohm's law, I = V ÷ R.

Opposition to current flow, measured in ohms (Ω). Higher resistance lets less current flow at a given voltage. R = V ÷ I.

The relationship between voltage, current, and resistance: V = I × R. Rearranged: I = V ÷ R and R = V ÷ I.

Electrical power equals voltage times current: P = V × I, measured in watts. Also P = I² × R.

The unit of electric current — the rate of charge flow. One amp equals one coulomb of charge per second.

The unit of electrical potential difference (pressure). It drives current through resistance.

The unit of electrical resistance. One ohm allows one amp to flow under one volt of pressure.

The unit of electrical power — the rate of doing electrical work. P = V × I.

A material (like copper) that allows electrons to flow easily because of low resistance.

A material (like rubber or plastic) that resists electron flow and is used to contain and direct current.

A material (like silicon) that conducts under some conditions and not others — the basis of diodes, transistors, and modules.

A circuit with one path. Current is the same everywhere, voltage divides across loads, and resistances add (R = R₁ + R₂ + …).

A circuit with multiple branches. Voltage is the same across each branch, current divides, and total resistance is less than the smallest branch.

A circuit combining series and parallel sections — common in real vehicle wiring with shared and branched paths.

A break in the current path so no current flows. The device is dead; a voltmeter reads source voltage up to the break, 0 beyond it.

An unintended low-resistance path. A short to ground bypasses the load, spikes current, and blows the fuse.

An unintended path to ground before the load. Current spikes and the fuse blows (or keeps blowing).

An unintended connection to battery voltage that can backfeed a circuit and operate a device when it should be off.

Unwanted resistance from corrosion, a loose/dirty connection, or a damaged wire. The device runs weak; voltage-drop testing locates it.

The voltage lost across a part while current flows. Measured under load, a high drop reveals unwanted resistance.

Measuring voltage across a wire/connection/ground with the circuit on and under load. Good connection drops near 0 V; under ~0.1 V is the goal.

The primary electrical test tool — measures voltage, current, and resistance. Its high input impedance loads the circuit very little.

A meter's internal resistance. High input impedance means the DMM draws almost no current, so it won't disturb sensitive circuits.

Done with the circuit de-energized and the component ideally isolated. The meter supplies its own test current; a live circuit gives a false reading.

The meter is connected in series so all current flows through it, or read with an inductive (clamp) ammeter around the wire.

The meter is connected in parallel (across) the part. Reads potential difference; done on a live circuit.

A meter that reads current by sensing the magnetic field around a wire — no need to break the circuit.

Checks for an unbroken path. The meter beeps/reads near 0 Ω if continuous; an open reads infinite (OL).

A sacrificial link that melts to open the circuit when current exceeds its rating, protecting the wiring from a short.

A resettable protective device that opens on overcurrent and either resets automatically or must be reset manually.

A short length of smaller-gauge wire that melts to protect a high-current circuit when a fuse would be impractical.

The common return path (usually the vehicle body/chassis) back to the battery negative. A bad ground causes high resistance and odd symptoms.

A drawing of how a circuit is connected, with components, colors, connectors, and grounds — essential for systematic diagnosis.

A device that communicates with vehicle modules to read DTCs, live data, freeze frame, and run bidirectional controls.

A standardized fault code a module stores when it detects a problem; read with a scan tool to point toward the affected circuit.

A scan-tool function that commands a module to operate an output (e.g., cycle a relay or motor) to confirm it works.

A simple lamp probe that lights when voltage is present. Useful for power/ground checks but cannot measure or load sensitive circuits.

A tool that indicates whether a point is high, low, or pulsing — useful on digital and module circuits.

Displays voltage over time as a waveform, revealing glitches, ripple, and signal patterns a DMM averages away.

A semiconductor that allows current in one direction only. Used in rectifiers and to block backfeed.

A semiconductor that switches or amplifies current; modules use transistors to control outputs.

A device that stores electrical charge and can smooth voltage or suppress noise in a circuit.

A component that adds a specific resistance to limit current or divide voltage in a circuit.

The sum of voltage drops around a series loop equals the source voltage — why voltage divides across series loads.

The positive/negative orientation of a circuit. Correct polarity matters for diodes, modules, and battery connections.

Probing a connector from the wire (back) side without disconnecting it, so the circuit can be tested live and under load.

The voltage actually reaching a load. Voltage drops in the wiring reduce available voltage and weaken the device.

The device that does the work in a circuit (lamp, motor, solenoid) and provides the resistance that limits current.

Generating voltage by moving a conductor through a magnetic field — the principle behind alternators and many sensors.

Open = no current (device dead, fuse OK). Short to ground = too much current (fuse blows).

So each device gets full battery voltage and one failure doesn't kill the others.

Add the resistances: R = R₁ + R₂ + R₃ + … More loads in series means more total resistance and less current.

Less than the smallest branch resistance, because added paths give current more ways to flow.

Voltage lost on the return (ground) path. Should be near 0 V; high ground drop dims or weakens a device.

Voltage drop tests under load and catches high resistance an ohmmeter on a dead circuit may read as fine.

Indicates a persistent short to ground; trace the circuit with the load disconnected to isolate the shorted section.

Always pull the wiring diagram, specs, and component locations before probing — systematic beats random.

The common automotive battery using lead plates in sulfuric-acid electrolyte. Provides ~12.6 V fully charged.

How full a battery is, judged by open-circuit voltage (~12.6 V = full) or specific gravity. Separate from capacity.

A rested battery's voltage with no load. ~12.6 V = full, ~12.4 V = ~75%, ~12.0 V = discharged.

The density of battery electrolyte vs. water, read with a hydrometer. ~1.265–1.280 indicates a full cell.

A tool that measures electrolyte specific gravity to judge state of charge per cell on non-sealed batteries.

Current a battery delivers at -18°C (0°F) for 30 seconds while holding ≥7.2 V. Rates cold-start ability.

Minutes a fully charged battery can supply ~25 amps at 27°C (80°F) before dropping to 10.5 V.

Applies ~half the CCA for 15 seconds; voltage must stay above ~9.6 V at 21°C (70°F) to pass.

An electronic tester that estimates battery capacity/CCA without applying a heavy load.

A battery must be charged to at least 75% before load testing, or the result unfairly fails it.

An Absorbed Glass Mat battery — sealed, spill-proof, with electrolyte held in glass mats; handles deep cycling and many accessories.

Key-off current the vehicle draws to keep memories alive. Excessive draw drains the battery overnight.

Ammeter in series with the battery (or low-current clamp) read after modules sleep; pull fuses to find the offending circuit.

Modules may take 20–60 minutes to power down after key-off; wait before reading parasitic draw or the value is falsely high.

Lead-sulfate crystals building on plates when a battery sits discharged, reducing capacity and the ability to take a charge.

A temporary higher voltage on a recently charged battery. Remove it (apply a brief load) before an accurate voltage reading.

White/blue buildup that adds resistance, causing voltage drop, hard starting, and charging complaints.

A high-current DC motor that cranks the engine for starting, drawing heavy amperage from the battery.

An electromagnet that engages the starter drive into the flywheel and switches the heavy starter current.

Measures cranking amps. High draw + slow crank = worn starter/dragging engine; low draw + slow crank = high cable resistance.

Measures drop on the positive cable, ground, and solenoid while cranking to find resistance in the starting circuit.

A switch that allows cranking only in Park or Neutral; a fault can cause a no-crank condition.

A relay that lets the ignition switch's small current control the heavy starter/solenoid current.

Often a low battery or high-resistance connection — the solenoid pulls in but can't sustain the heavy starter current.

Discharged/weak battery, high-resistance cables or grounds, a dragging starter, or a mechanically tight engine.

A one-way clutch in the starter drive that lets the engine spin faster than the starter without driving it back.

Heavy-gauge cables carry hundreds of cranking amps; undersized or corroded cables add resistance and cause slow cranking.

A device that maintains module/clock/radio memory while the battery is disconnected for service.

Remove the negative (ground) terminal first and reconnect it last to avoid sparks and shorts.

A sealed lead-acid battery you cannot add water to; state of charge is checked by voltage or a built-in eye, not a hydrometer.

Standard modern vehicles connect the battery negative to the chassis as the common return path.

Connect positive to positive, then negative to a good engine ground (not the dead battery) to reduce spark risk.

Keeps the battery topped up and powers loads while the engine runs, using the alternator and voltage regulator.

A belt-driven generator that spins a rotor in a stator to make AC, then rectifies it to DC for the vehicle.

The spinning electromagnet inside the alternator; field current through it controls how much voltage the alternator makes.

The stationary windings in the alternator where AC voltage is induced as the rotor's magnetic field sweeps past.

The diodes that convert the alternator's AC into DC. A failed diode causes high AC ripple and low output.

Controls the rotor field current to hold charging voltage in range (~13.5–14.5 V). Often built into the alternator or PCM.

Roughly 13.5–14.5 V at the battery with the engine running and loads on.

Leftover AC in the alternator's DC output. Excessive ripple (DMM AC scale, often >0.5 V) = a failed rectifier diode.

Measure voltage and amperage at the battery with loads on. Too low = undercharge; too high = overcharge.

Charging voltage too low, leaving a discharged battery. Causes: bad regulator, worn brushes, slipping belt, high circuit resistance.

Charging voltage too high, boiling/gassing the battery and shortening its life. Usually a faulty voltage regulator.

Drop on the alternator's output (B+) wire and ground that reduces voltage reaching the battery; tested under charging load.

Drives the alternator. A loose, glazed, or worn belt slips and causes low or erratic charging.

Keeps the serpentine belt at correct tension automatically; a weak tensioner causes belt slip and charging problems.

Lets the regulator sense system/battery voltage so it can adjust charging output accurately.

The dash light that warns of a charging fault; it should go out once the engine runs and the alternator charges.

An open diode lowers output and raises AC ripple; a shorted diode can drain the battery (a key-off current path).

On many vehicles the PCM commands the alternator's field for smart charging based on load, temperature, and battery state.

Bypassing the regulator to force maximum alternator output, used to isolate a regulator fault from an alternator fault.

Turn on accessories and verify the alternator maintains voltage and supplies rated current under load.

Low/erratic charging voltage and possible squeal — check belt tension and condition before condemning the alternator.

Good rectification shows even humps; a missing/uneven hump indicates an open or shorted diode.

A headlamp that heats a filament inside a halogen-gas capsule — a simple resistive load.

A high-intensity-discharge headlamp that strikes an arc using a high-voltage ballast/igniter. Don't touch the capsule; respect the high voltage.

A light-emitting-diode lamp using semiconductors and a driver; draws little current. One failed LED/driver can dim or kill it.

The unit that supplies the high-voltage startup pulse and regulated current to ignite and run an HID lamp.

Adjusting headlight beam aim to spec so the road is lit without blinding oncoming drivers.

A rapid turn-signal flash signaling a burned-out (or low-current) bulb on that side. LED conversions can trigger it.

The device that cycles the turn signals on and off. Many modern systems flash via the BCM rather than a thermal flasher.

A resistor added to an LED turn signal so the system sees normal current and doesn't read 'bulb out' (hyperflash).

A switch at the brake pedal that turns on the brake lights (and signals other modules) when the pedal is pressed.

Lights that run automatically when the vehicle is on, for visibility; often dimmed headlights or dedicated lamps.

The steering-column switch that operates turn signals, high/low beam, headlights, and often wipers.

Selects between low and high headlight beams; built into the multifunction switch on most vehicles.

Dome and door lights, often controlled by door switches and the BCM with a timed delay.

An open in that branch — a burned bulb, bad socket, corroded connector, or broken wire.

Usually a high-resistance connection or ground; confirm with a voltage-drop test rather than replacing the bulb.

Points to a shared cause — the BCM, a common ground, a master switch, or a network fault — not one bulb.

A relay that switches the high headlight current so the switch only carries the small control current.

A headlamp assembly with a replaceable bulb in a fixed housing/lens, rather than a one-piece sealed beam.

An older one-piece headlamp where the filament, reflector, and lens are sealed together and replaced as a unit.

A light sensor that switches headlights on automatically in darkness via the BCM.

Some systems sense bulb current; a low-current LED or an open bulb triggers a 'lamp out' or hyperflash warning.

A blue dash telltale confirming the high beams are on, driven by the headlight/multifunction circuit.

The networked module that displays speed, RPM, temperature, fuel level, and warnings, reading most data over a data bus.

A sensor (e.g., a fuel-tank float-and-rheostat) whose changing resistance reports a value to a gauge or module.

A float and variable resistor in the tank; its resistance changes with level to drive the fuel gauge.

Driven by a temperature sender (thermistor) whose resistance changes with engine coolant temperature.

A temperature-sensitive resistor used in temperature senders; resistance changes predictably with temperature.

Vehicle speed comes from a vehicle speed sensor or wheel-speed data sent over the bus to the cluster.

Displays engine RPM, taken from the engine/ignition signal and sent to the cluster.

An indicator light (oil, charge, ABS, airbag) that alerts the driver to a system condition or fault.

The brief lighting of warning lamps at key-on to prove the bulbs/LEDs work; a missing telltale may be a burned indicator.

Usually a power, ground, or data-bus fault — not a single gauge.

Usually the gauge's sender or wiring, not the cluster — confirm the sender's resistance against spec.

Often an open or out-of-range sending-unit circuit or a bad sender ground; measure sender resistance at empty and full.

Often a shorted sending-unit circuit or a sender grounded internally; check resistance and wiring.

Mileage stored electronically in the cluster (or another module) rather than mechanical gears.

A display that shows trip data, warnings, and messages, fed by the cluster/BCM over the network.

A built-in diagnostic mode that sweeps gauges and lights telltales to confirm the cluster's operation.

Most gauges get values as digital messages over a bus (e.g., CAN); a bus fault can blank or freeze the cluster.

Driven by an oil-pressure sender or switch; a lamp warns of low pressure, a gauge shows the value.

A dash gauge showing system/charging voltage so the driver can spot a charging problem.

Provides audible warnings (key-in-ignition, seatbelt, door ajar), often driven by the BCM.

A poor sender ground raises resistance and skews the gauge reading — a common cause of inaccurate gauges.

Modern analog gauges use a small stepper motor moved by the cluster; the needle is positioned electronically.

An older electromagnetic gauge whose needle position depends on current through its coils from the sender.

Always verify the cluster's switched power, constant power, and ground before condemning it.

An algorithm in the cluster/PCM that estimates service intervals and displays reminders to the driver.

Stepper-motor clusters sweep the needles to confirm gauge operation during the prove-out.

Often a loose connector, flexing wire, or marginal ground; wiggle-test and check connections under load.

An electrically operated switch: a small coil current closes contacts to carry a much larger load current.

The coil (control) side is low current; the contact (load) side carries the high current to the device.

Swap an identical relay, check coil resistance, confirm the coil energizes, and verify switched voltage at the output.

An electromagnet that moves a plunger to do mechanical work, such as door locks or the starter drive.

The module managing many body accessories — lighting, locks, windows, wipers, chimes — and communicating over the network.

Letting modules share data over a small two-wire network (a bus) instead of a separate wire per signal, cutting wiring weight.

A common two-wire vehicle data bus for module communication. A bus fault can disable several systems at once.

A DTC indicating a module has lost communication on the bus; read with a scan tool to find the dropped module.

Switching a load on/off rapidly and varying the on-time (duty cycle) to control average power — used for motors and dimming.

The percentage of time a PWM signal is on within each cycle. A higher duty cycle delivers more average power.

A reversible DC motor that raises/lowers a window, often PWM-controlled with anti-pinch protection.

A feature that reverses a power window if it senses an obstruction while closing, for safety.

A solenoid or small motor that locks/unlocks a door on command from the switch or BCM/remote.

The HVAC fan motor, controlled by a resistor pack (stepped speeds) or a PWM module (variable speed).

Adds resistance to drop voltage for lower blower speeds. A burned resistor often leaves only high speed working.

Drives the wipers; the park switch returns the blades to the rest position when switched off.

Usually a relay-controlled circuit triggered by the horn switch; a dead horn is often a relay or its control.

A radio-frequency remote that locks/unlocks and arms the vehicle via a receiver and the BCM.

A security system that prevents starting unless a recognized key/transponder is present.

A key with an embedded chip the immobilizer reads to authorize starting.

Resistive heating elements controlled by switches/relays or the BCM; diagnosed like any heated-load circuit.

A grid of resistive lines on the glass that heat to clear fog/frost; a break opens that line.

A system that maintains set speed using throttle control and inputs over the network.

Networked modules and amplifiers; diagnosed for power, ground, and bus communication like other body electronics.

Driver-assist accessories tied into the BCM/network and a display, common on modern vehicles.

A reversible motor with a control module that slides/tilts the sunroof, often with pinch protection.

Updating or configuring a module's software with a scan tool, sometimes required after replacement.

Shared ground points serving multiple accessories; a bad shared ground causes odd, multi-system symptoms.

Voltage feeding a circuit through an unintended path (e.g., a shared ground), causing a device to operate oddly.

Contacts that are open until the coil energizes, then close to power the load.

Contacts that are closed until the coil energizes, then open.

Repairing corroded or spread terminals and bad connections — a frequent root cause of body-electrical faults.

Service-information data showing where modules, grounds, splices, and connectors are physically located.

A point where several wires join; a failed splice can affect multiple circuits at once.

A fuse/relay box with built-in control electronics, often performing BCM-style functions.

The BCM commands many accessories and shares status over the bus, so its faults can affect several systems.

Confirm power in, ground, the control signal (switch/module), and the device itself — in that order.

A scan tool can show which modules respond on the bus, helping pinpoint a lost module or wiring fault.

Corroded terminals and grounds add resistance, the most common cause of dim lights, slow motors, and odd faults.