A school bus blower motor circuit reads 12.6V at the battery but only 10.2V at the motor with the motor running. What does this indicate?
General Electrical Diagnosis
Question · Medium
Using Ohm's law, what current flows through a 6-ohm school bus dome lamp connected to a 12V source?
Question · Easy
Tech A says a digital multimeter set to DC volts should be connected in parallel with the component being tested. Tech B says an ammeter is connected in series. Who is correct?
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What is the maximum allowable voltage drop on a typical school bus 12V starter ground cable during cranking?
A wiring diagram shows a circuit with two 4-ohm resistors in series across 12V. What is the total current?
Two 6-ohm bulbs are wired in parallel on a 12V circuit. What is the total circuit current?
When using a clamp-type DC ammeter to measure starter draw on a school bus, the clamp should be placed around:
An ohmmeter reads OL (infinite) when connected across a school bus relay coil that should measure about 80 ohms. This indicates:
A school bus circuit blows its fuse immediately every time it is replaced and the switch is on. The most likely cause is:
What does a wiring diagram symbol of a zigzag line typically represent?
A technician finds 0V on both sides of a closed switch in an energized circuit using a voltmeter referenced to ground. The switch is:
Question · Hard
Power equals voltage times current. A school bus accessory draws 5 A at 12V. What is its power consumption?
Tech A says insulated (positive) side voltage-drop testing should be done with the circuit loaded and operating. Tech B says zero current must flow to get an accurate voltage-drop reading. Who is correct?
A heavy-duty school bus uses two 12V batteries connected in parallel. The resulting system voltage and capacity are:
Battery Diagnosis Service
During a battery open-circuit voltage test, a fully charged 12V lead-acid battery should read approximately:
When load testing a school bus battery, the carbon-pile or electronic load is typically applied at:
A 12V battery under a proper load test holds 9.6V at 70 degrees F. The battery is:
A battery hydrometer measures specific gravity to determine:
Tech A says corroded battery terminals can cause hard starting. Tech B says a parasitic (key-off) drain can discharge a school bus battery overnight. Who is correct?
To measure parasitic draw on a parked school bus, a technician should connect the ammeter:
White, crusty buildup on a school bus battery terminal is most commonly:
A school bus park/clearance lamp circuit shares a single fuse with the side marker lamps. If that fuse opens, the result is:
Lighting Systems Diagnosis
A battery conductance tester reports a battery is good but at a low state of charge. The correct next step is to:
A school bus equipped with a battery master disconnect switch will not crank in any gear. The disconnect is in the main negative path. The technician should first verify:
Starting System Diagnosis
A school bus engine cranks slowly. Battery is fully charged and passes a load test. The next logical test is:
A starter current draw test shows high current draw and slow cranking. This most likely indicates:
A starter draw test shows low current draw and slow cranking with a good battery. The most likely cause is:
During cranking, the voltage at the starter motor terminal must remain above approximately what value for proper operation on a 12V system?
A school bus will not crank in PARK but cranks in NEUTRAL. The most likely cause is:
A starter solenoid has two large terminals and a small control terminal. The small terminal:
Tech A says a clicking starter solenoid with no cranking can be caused by a discharged battery. Tech B says it can be caused by high resistance in the starter feed cable. Who is correct?
A starter motor that spins but does not engage the flywheel ring gear most likely has a problem with the:
A voltage-drop test across the starter solenoid main contacts during cranking should not exceed approximately:
A school bus uses a heavy-duty starter relay in the start control circuit primarily to:
An open in the starter pull-in winding of the solenoid would most likely cause:
The starter motor on a school bus completes its high-current circuit to ground through the:
A school bus alternator's primary function is to:
Charging System Diagnosis
With the engine running at 1500 rpm and lights on, charging system voltage should typically be approximately:
A school bus charging system test shows 16.5V at the battery with the engine running. This indicates:
Excessive AC ripple voltage measured at the battery with the engine running usually indicates:
An alternator output (charging) test is performed by:
Tech A says a slipping or glazed alternator drive belt can cause low charging output. Tech B says a high voltage drop in the charging circuit can cause an undercharged battery. Who is correct?
A voltage-drop test on the alternator B+ output cable to the battery positive should not exceed approximately:
A school bus charge (battery) warning lamp stays on with the engine running. The first check should be:
On many heavy-duty school bus alternators, the regulator controls output by varying:
An alternator produces no output. Bench testing shows an open rotor (field) winding. The result is:
A school bus equipped with dual alternators commonly uses them to:
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