ASE T6 Electrical/Electronic Systems (Medium/Heavy Truck) key terms

A measurement of how much voltage is lost across a conductor, connection, or component while current flows; excessive drop indicates high resistance such as a corroded terminal or undersized cable.

The relationship stating that voltage equals current multiplied by resistance; technicians use it to predict circuit behavior and to calculate expected values when diagnosing opens, shorts, and excessive resistance.

A circuit with only one path for current, so the same current flows through every component and total resistance is the sum of individual resistances; an open anywhere stops all current flow.

A circuit providing two or more current paths between the same two points, so each branch sees the same voltage and total resistance is lower than the smallest branch resistance.

The return path that carries current back to the battery negative terminal, usually through the chassis and engine block; poor grounds cause dim lights, slow cranking, and erratic electronics.

A flexible braided cable bonding the engine, frame, or cab to the battery negative; it must carry heavy starter current and is a common source of cranking and charging complaints when corroded.

Current that flows from the battery when the ignition is off and all accessories are off; measured in milliamps, it reveals a module or relay that fails to sleep and drains the battery.

A table that converts a measured voltage across a fuse into approximate current flow, allowing a technician to locate a parasitic draw or overloaded circuit without removing the fuse.

A handheld instrument that measures voltage, resistance, current, and often frequency or duty cycle; selecting the correct function and range is essential to avoid damage or misleading readings.

A test instrument that graphs voltage over time, letting a technician see signal shape, glitches, and pulse width that a multimeter averages out or misses entirely.

The percentage of time a digital signal or pulse-width-modulated output is on during one complete cycle; used to control lamp brightness, motor speed, and actuator position.

A method of controlling average power to a load by rapidly switching voltage on and off and varying the on-time; common in blower motors, lighting, and solenoid drivers.

A twisted-pair serial network that lets electronic control modules share data; faults appear as communication codes, and voltage or resistance checks at the DLC help isolate the problem.

The standardized 16-cavity diagnostic socket under the dash that provides battery power, ground, and access to network and module data for a scan tool.

A computer interface that communicates with vehicle modules to read and clear diagnostic trouble codes, view live data, and run bidirectional tests.

An alphanumeric code stored by a control module when it detects a fault or out-of-range condition; the code identifies the circuit or system, not necessarily the failed part.

A snapshot of operating conditions such as speed, load, and temperature recorded at the moment a diagnostic trouble code set, helping a technician reproduce the fault.

A resistor at each end of a high-speed CAN network that maintains proper bus impedance; a missing or failed resistor causes communication errors and abnormal bus voltage readings.

The current a battery can deliver for 30 seconds at zero degrees Fahrenheit while maintaining at least 7.2 volts; the primary rating for comparing starting batteries.

The number of minutes a fully charged battery at 80 degrees Fahrenheit can supply 25 amps before falling below 10.5 volts; it indicates how long the vehicle can run if the alternator fails.

The percentage of a battery's capacity currently available, estimated from open-circuit voltage after the battery has rested; used to decide whether to charge before testing.

A test applying a heavy current draw to a fully charged battery while watching voltage; a battery that falls below the specification is weak or failed and must be replaced.

An instrument that estimates battery condition by measuring its internal conductance; fast and safe, but results are invalid on a discharged or recently charged battery.

The ratio of a battery electrolyte's density to water, measured with a hydrometer; it indicates state of charge and can reveal a shorted or mismatched cell.

An electromagnetic switch that, when energized by the ignition circuit, engages the starter drive and closes heavy contacts to send battery current to the starter motor.

The low-current wiring from the ignition switch through relays, neutral switches, and the solenoid coil; excessive voltage drop here prevents the solenoid from engaging.

A measurement of amperage the starter motor consumes while cranking, using an inductive clamp; high draw suggests internal drag or a worn motor, low draw suggests excessive resistance.

A switch that prevents starter operation unless the transmission is in park or neutral, or the clutch pedal is depressed; it also often controls reverse lamps.

A belt-driven generator that produces alternating current, rectifies it to direct current, and regulates output to charge the battery and power vehicle loads while the engine runs.

The control device inside or external to the alternator that limits charging voltage to a set range, typically about 13.5 to 14.5 volts, protecting the battery and electronics.

A set of diodes that converts the alternator's alternating current into direct current; a failed diode causes low output and excessive AC ripple.

The small alternating-current component remaining in a direct-current charging system; excessive ripple indicates a failed diode or stator problem and can disturb electronic modules.

A circuit that reports actual battery voltage to the voltage regulator so it can adjust output; high resistance in this wire causes overcharging or undercharging.

Adjusting a headlamp's vertical and horizontal aim to the manufacturer's specification so the beam lights the road without glaring oncoming drivers.

An incandescent lamp containing halogen gas that redeposits tungsten on the filament; it runs hot, so glass must not be touched with bare fingers.

A semiconductor light source with long life and low current draw; it requires correct polarity and a compatible driver, so it cannot always be substituted for a bulb.

A lighting arrangement where a module controls lamps over a shared network or pulse-width-modulated wire rather than individual switched feeds, changing how faults are diagnosed.

A variable-resistance sensor that converts a physical value such as pressure, temperature, or fuel level into an electrical signal for the gauge or module.

The instrument assembly containing speedometer, tachometer, and gauges; most modern clusters are modules that receive data over the network rather than direct sensor wires.

An indicator illuminated by a module to alert the driver to a fault or condition; a bulb-check circuit proves the lamp works at key-on.

An electric motor that drives the windshield wiper linkage, often with a park switch and multiple speed or intermittent control through a module or resistor.

A switch inside or on the wiper motor that keeps the motor powered until the blades reach their stowed position, then cuts the circuit so they stop correctly.

A small electric pump that pressurizes washer fluid to the nozzles; it is controlled by a dash switch or module and shares the wiper control circuit on many trucks.

An electromagnetic switch that lets the low-current horn button control the high current drawn by the horn; a failed relay or clock spring can silence the horn.

The path from battery through fuse, relay, horn button, and horn to ground; testing each point for voltage and ground quickly isolates a no-honk complaint.