ASE S6 Electrical/Electronic Systems (School Bus) common mistakes
ASE S6 Electrical/Electronic Systems (School Bus) · Understand the traps and how to avoid them.
When a circuit blows a fuse, immediately installing a higher-amperage fuse or wrapping the blown fuse in foil to 'get it working' instead of finding the short.
Candidates confuse the fuse with the fault; they treat the blown fuse as the problem rather than as a symptom of excessive current draw, and they want the load to operate during the test.
What to do instead
Always replace a fuse with the same rating, then isolate the circuit and measure current draw or resistance to ground to locate the excessive load or short before restoring power.
Testing a battery only with a voltmeter and declaring it good because it reads about 12.6 V, skipping a load/capacity test.
Open-circuit voltage reflects state of charge, not cranking capacity; candidates equate 'charged' with 'healthy' and skip conductance or load testing.
What to do instead
Perform a conductance (electronic) test or a carbon-pile load test to the battery's CCA rating, and check state of charge first so the result is valid.
Judging battery condition or alternator output without first cleaning and tightening terminals, or measuring charging voltage at the battery posts instead of across the battery itself after a load.
Candidates chase the component before verifying connections; corroded or loose terminals create voltage drops that mimic a failed battery or alternator.
What to do instead
Clean and torque terminals to spec, then perform a voltage-drop test on both the ground and the positive side of the charging and cranking circuits before condemning any component.
Replacing the starter because it 'won't crank' without first checking control-circuit voltage at the starter solenoid terminal and performing a voltage-drop test on the cables.
The symptom points at the starter, so candidates skip the control side and the cable resistance, assuming the motor is at fault.
What to do instead
Verify battery state of charge, then measure voltage at the S terminal during crank and do voltage-drop tests on B+ and ground cables; only condemn the starter when it receives full voltage and current and still fails to crank.
Diagnosing a no-crank as a starter fault when the neutral safety switch, clutch switch, or (on school buses) the hood/emergency-exit interlock is preventing crank.
Candidates overlook the starting interlock chain, which on school buses includes safety switches that are not present on light vehicles.
What to do instead
Trace the control circuit from ignition switch through the neutral/safety interlocks to the solenoid, verifying voltage at each point in the chain before condemning the starter.
Measuring alternator output at idle with no electrical load and calling the charging system good, or condemning the alternator for low voltage without checking belt condition and tension.
Candidates test at the easiest condition and forget that output must be verified under load and at specified rpm, and that a slipping belt mimics a failed alternator.
What to do instead
Check belt condition and tension, then measure charging voltage at the battery with the engine at the specified rpm and a load applied (lights, blower, accessories) against manufacturer specification.
Chasing a lamp that 'won't light' by replacing the bulb repeatedly without checking ground, socket corrosion, and voltage drop on the feed circuit.
The bulb is the visible, easy part to swap; candidates stop at the load and don't verify the circuit path.
What to do instead
Verify power and ground at the socket with a test light or meter, measure voltage drop on the feed and ground sides, then replace the bulb only after the circuit is proven good.
Treating a fast-flashing turn signal or a lamp that stays on as a bulb problem without checking the flasher, the lamp ground, or the school-bus-specific wiring for the warning-lamp system.
Candidates apply light-vehicle assumptions and miss that flash rate and lamp behavior are driven by the flasher and by body-builder wiring.
What to do instead
Check the flasher and its ground, verify each lamp's ground and filament, and consult the body-builder schematic for the specific warning-lamp circuit before replacing parts.
Diagnosing an inoperative gauge or warning lamp by replacing the sender or the cluster without first checking the ground, the reference voltage, and the data bus/communication circuit.
Candidates treat instrumentation as a single component and don't separate sensor, wiring, and cluster, nor do they check for communication faults on modern multiplexed buses.
What to do instead
Verify the cluster's power and ground, check the sensor signal at the cluster connector against specification, and scan for communication or body-controller codes before replacing any module.
On school-bus-specific systems (stop arm, crossing gate, eight-way warning lights, child-check system, camera/GPS/radio), diagnosing by swapping the motor or module without verifying the body-builder control inputs and interlocks (ignition, park brake, door switch).
These systems are built by the body manufacturer and depend on interlocks and inputs that candidates don't trace; they assume the actuator is at fault.
What to do instead
Obtain the body-builder wiring diagram, verify each enabling input and interlock at the controller, then test the actuator only after the control inputs are confirmed correct; document the circuit path checked.