ASE S6 Electrical/Electronic Systems (School Bus) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

Voltage equals current multiplied by resistance (V = I × R). Used to predict circuit behavior and to calculate expected voltage drops across known resistances.

Voltage drop test

Measures voltage lost across a conductor or connection while current flows. Excessive drop (over about 0.5 V on a power path) indicates high resistance.

Parasitic draw

Key-off current consumed by modules and accessories. Measured with a clamp or series ammeter after modules sleep, compared to manufacturer specification.

CAN bus termination

Twisted-pair network ends are terminated near 120 ohms each. Two parallel terminations read about 60 ohms across the bus when isolated.

Open-circuit voltage

Resting battery voltage indicating state of charge: about 12.6 V is 100 percent, 12.4 V is 75 percent, and 12.2 V is 50 percent.

Battery load test

Applies about half the CCA rating for 15 seconds. A fully charged battery should stay at or above 9.6 V at 70 degrees Fahrenheit.

Cold cranking amps

Amperes a battery delivers at 0 degrees Fahrenheit for 30 seconds while maintaining at least 7.2 volts across the terminals.

Reserve capacity

Minutes a fully charged battery sustains 25 amperes at 80 degrees Fahrenheit before falling to 10.5 volts.

Cranking voltage drop limits

Maximum acceptable drop is typically 0.5 V on the insulated circuit and 0.2 to 0.3 V on the ground circuit during cranking.

Starter solenoid function

Engages the drive pinion with the flywheel ring gear and closes high-current contacts that energize the starter motor.

Neutral start switch

Prevents cranking unless the transmission is in park or neutral. On school buses it also blocks cranking in reverse and drive.

Starter current draw test

Measures amperes during cranking. Excessive draw with slow cranking suggests a shorted armature, worn bushings, or a binding engine.

Alternator regulated voltage

Charging output is typically held between 13.5 and 14.8 volts, varying with temperature and battery state of charge.

Rectifier bridge

Diodes that convert alternator AC output to DC. A failed diode causes ripple and reduced output, detectable with an AC voltmeter.

Field excitation

Current supplied to the rotor winding to create the magnetic field. Without excitation the alternator cannot produce charging output.

Overvoltage condition

Charging voltage above about 15 volts indicates a failed voltage regulator and can damage electronics and overheat the battery.

Turn signal flasher load

Flasher timing depends on lamp current. LED conversions may need an electronic flasher to prevent fast blink or no blink.

FMVSS 108

Federal standard governing lighting and reflective devices, including required color, location, and intensity of school bus warning lamps.

Ground-side lamp fault

A poor ground at a lamp causes dim glow or cross-feed through shared filaments, making unrelated lamps appear to operate.

Headlamp relay purpose

Relays carry high lamp current so the switch and small-gauge harness do not overheat, extending switch and wiring life.

Gauge sender circuit

Sending units vary resistance with temperature or pressure. A pegged gauge often indicates an open or shorted sender circuit.

Cluster prove-out

At key-on the cluster illuminates warning lamps to verify bulb and circuit function. A lamp that never lights indicates a fault.

Vehicle speed sensor

Generates a signal proportional to output shaft or wheel speed. The cluster or ECM converts it to speedometer and odometer readings.

Data bus gauge failure

A single bus fault can blank multiple gauges and warning lamps at once, so check bus voltage and termination before replacing the cluster.

Reversible motor circuit

Power windows and seats reverse direction by reversing polarity through switches or paired relays; both feeds and grounds must be verified.

Relay coil and contacts

The coil is a low-current control circuit tested by resistance; contacts are the high-current path tested for continuity and voltage drop.

Wiper park switch

Returns wiper blades to the rest position when switched off. Failure to park indicates a park switch or wiring fault.

Body control module

Module controlling interior lighting, wipers, and accessories. Scan tool data shows inputs and outputs for diagnosis.

Eight-way warning lamps

Red lamps flash during loading and unloading with the stop arm extended; amber lamps warn drivers of an approaching stop.

Stop arm interlock

Circuit logic that allows the stop arm to extend only when red warning lamps flash and the door is open, per state regulation.

Child-check system

Post-trip reminder requiring the driver to walk to the rear and actuate a device within a time limit, or an alarm sounds.

Radio antenna ground plane

Metal body area beneath the antenna that provides the counterpoise. Poor ground plane causes reduced range and increased noise.