ASE H6 Electrical/Electronic Systems (Transit Bus)

A transit bus 24 V accessory circuit draws 3 A through a load with 6 ohms of resistance. Using Ohm's law, what voltage is dropped across that load?

• A18 V
• B12 V
• C6 V
• D24 V

Technician A says voltage-drop testing is performed with the circuit energized and operating under load. Technician B says a good ground connection should drop more than 0.5 V. Who is correct?

• ANeither A nor B
• BTechnician B only
• CBoth A and B
• DTechnician A only

Which meter setting is used to confirm that a relay coil is not internally open before replacing the relay?

• ADC voltage
• BFrequency (Hz)
• CAC current
• DResistance (ohms)

A clamp-style ammeter is the preferred tool for measuring high starter current on a transit bus primarily because it:

• AMust be wired in series with the starter cable
• BMeasures resistance more accurately than a DMM
• COnly works on AC circuits
• DReads current without breaking the circuit

Two 6-ohm resistors are connected in parallel in a body control circuit. What is the total resistance of the parallel combination?

• A2 ohms
• B12 ohms
• C6 ohms
• D3 ohms

When reading a transit bus wiring diagram, a solid line connecting two components that does NOT pass through any connector or splice symbol indicates:

• AA continuous conductor with no intermediate connection
• BA shielded data bus only
• CA chassis ground path
• DAn optional accessory circuit

A bus circuit blows its fuse only when a particular accessory is switched on. The most likely cause is a:

• AOpen in the load device
• BHigh-resistance ground connection
• CShort to ground that completes when the accessory is energized
• DCorroded but functional switch contact

A 24 V circuit should deliver full voltage to a lamp, but the technician measures 24 V at the source and only 19 V at the lamp with the lamp on. This 5 V loss most directly indicates:

• AA short to ground before the lamp
• BAn open ground at the lamp
• CExcessive resistance (voltage drop) in the feed circuit
• DA correctly operating circuit

On a J1939 CAN datalink, the two terminating resistors are each:

• A60 ohms, giving 120 ohms total across the bus
• B12 ohms, giving 24 ohms total across the bus
• C120 ohms, giving 60 ohms total across the bus
• DOpen circuits used only for shielding

A technician measures resistance across the J1939 bus (key off, modules powered down) and reads about 60 ohms. This indicates:

• AAn open in the CAN backbone
• BOne terminating resistor is missing
• CA short between CAN_H and CAN_L
• DBoth terminating resistors are present and the bus is likely intact

Technician A says a multiplexed body controller reduces the number of physical wires by sending commands over a data bus. Technician B says multiplexing eliminates the need for any input switches on the bus. Who is correct?

• ATechnician B only
• BTechnician A only
• CBoth A and B
• DNeither A nor B

The least intrusive first step when diagnosing an intermittent body-electrical complaint on a multiplexed bus is to:

• AReplace the body control module
• BRetrieve stored and active diagnostic trouble codes with a scan tool
• CCut the harness to inspect every wire
• DDisconnect the batteries for an hour

A solenoid in a transit bus circuit converts:

• AElectrical energy into linear mechanical motion
• BMechanical motion into voltage
• CAC voltage into DC voltage
• DHeat into electrical current

A circuit has a 24 V source and a single load. A DMM placed across the open switch with the switch OFF and the load connected reads 24 V. This reading is:

• AA fault indicating a shorted switch
• BAn indication of an open ground
• CNormal because the open switch drops the full source voltage
• DCaused by a blown fuse

Excessive resistance in a series circuit will cause circuit current to:

• AIncrease
• BStay exactly the same
• CDecrease
• DReverse direction

When using a DMM to back-probe a sensor connector on a live transit bus circuit, the technician should:

• APierce the insulation with the probe to ensure contact
• BUse the resistance setting while the circuit is energized
• CDisconnect the connector first and probe the open terminals
• DInsert the probe alongside the terminal from the wire side without damaging the seal

A wiring diagram shows a circuit protected by a 15 A fuse feeding a relay-controlled lamp circuit. The relay coil is energized but the lamp does not light and the fuse is good. The fault is most likely in the:

• ARelay load (switched) contacts or the lamp circuit downstream
• BRelay coil control side only
• CFuse only
• DBattery main disconnect

A parasitic (key-off) battery drain test on a transit bus is best measured with the meter set to:

• AOhms across the starter
• BDC volts across the battery posts
• CAC volts at the alternator
• DDC milliamps/amps in series with the disconnected battery cable

A circuit with a 24 V source draws 4 A. What is the total circuit resistance?

• A4 ohms
• B8 ohms
• C6 ohms
• D12 ohms

Technician A says a CAN bus with one terminating resistor disconnected can still communicate but is prone to errors. Technician B says shorting CAN_H to CAN_L will typically stop all communication on that bus. Who is correct?

• ABoth A and B
• BTechnician B only
• CTechnician A only
• DNeither A nor B

A grounded (short-to-ground) circuit on the supply side of a fuse will most likely:

• AOpen the fuse as soon as power is applied
• BDim the load slightly
• CHave no effect until the switch is closed
• DIncrease battery voltage

On a transit bus schematic, a component shown with a coil symbol and a separate set of contacts that are normally open (NO) is a:

• ADiode
• BRelay
• CResistor
• DCapacitor

A reading of OL (over-limit/infinite) on an ohmmeter connected across a wire that should be continuous indicates:

• AA dead short
• BAn open (broken) conductor
• CNormal low resistance
• DReversed polarity

When performing a voltage-drop test on the positive feed of a transit bus headlight circuit, the maximum acceptable total drop on the feed side is generally considered to be about:

• A0.0 V exactly
• BNo more than roughly 0.5 V on the insulated side
• CAt least 5 V
• DEqual to source voltage

A scan tool shows a J1939 SPN/FMN diagnostic message reporting 'voltage above normal' for a circuit. This FMI category most directly points to a:

• AShort to ground
• BNormal operating condition
• CShort to a voltage source or open with pull-up giving high reading
• DMechanical bearing failure

A technician needs to find which of several parallel branches has a fault that is drawing excess current. The best approach is to:

• AMeasure source voltage only
• BCheck the chassis paint thickness
• CReplace all branch loads
• DUse a clamp ammeter on each branch to compare current draw

A diode used as a relay coil spike suppressor should be installed:

• AForward-biased so it conducts during normal coil operation
• BIn series with the coil to limit current
• CReverse-biased across the coil so it conducts only the inductive kick
• DAcross the battery main terminals

Technician A says a DMM should be set to a current range and connected in series to measure circuit current. Technician B says a DMM measuring voltage is connected in parallel across the component. Who is correct?

• ATechnician A only
• BTechnician B only
• CBoth A and B
• DNeither A nor B

A high-resistance connection in a transit bus accessory ground will most likely cause the accessory to:

• AOperate at higher than normal voltage
• BOperate weakly or erratically due to reduced current
• CDraw zero current with the switch open
• DIncrease alternator output

Two loads draw 2 A and 3 A on the same 24 V parallel bus bar. Total current supplied by the source for just these two loads is:

• A1 A
• B5 A
• C6 A
• D24 A

During electrical diagnosis, the FIRST verification step before extensive testing should be to:

• AReplace suspect components
• BFlash-program all modules
• CConfirm the customer complaint and check the basics such as fuses, grounds, and battery s…
• DRemove the dash to inspect every wire

A wiring diagram callout reads '#10 GA' for a conductor while the rest of a branch uses '#16 GA.' The larger '#10' conductor is most likely used because that segment:

• ACarries higher current and needs lower resistance
• BIs a ground-only wire that carries no current
• CIs a data bus requiring twisted pair
• DIs an optional circuit not normally connected

Two heavy-duty 12 V AGM batteries are connected in series on a transit bus. The resulting system voltage and capacity behavior is:

• A24 V at the same amp-hour capacity as one battery
• B12 V at double the amp-hour capacity
• C24 V at double the amp-hour capacity
• D12 V at the same amp-hour capacity

Two identical 12 V batteries connected in parallel provide:

• A24 V at single-battery capacity
• B6 V at single capacity
• C24 V at double capacity
• D12 V at double the amp-hour capacity

An AGM (absorbed glass mat) heavy-duty battery differs from a conventional flooded battery primarily because it:

• AUses a gel that must be refilled with water
• BHolds electrolyte in a glass mat, is sealed, and is more vibration resistant
• COperates at 6 V instead of 12 V
• DCannot be deep cycled at all

A maintenance-free AGM battery should be tested for state of health using:

• AA hydrometer to read specific gravity of each cell
• BAn electronic conductance/load tester and an open-circuit voltage reading
• COnly a visual inspection of the case
• DA tachometer

A fully charged 12 V flooded lead-acid battery at rest should read an open-circuit voltage of approximately:

• A10.5 V
• B11.5 V
• C15.0 V
• D12.6 V

When load testing a 12 V battery, a common rule is to apply a load of one-half the CCA rating for 15 seconds. A good battery should maintain a voltage of at least about:

• A9.6 V at 21 C (70 F)
• B7.2 V at 21 C (70 F)
• C12.6 V at 21 C (70 F)
• D14.4 V at 21 C (70 F)

Technician A says corroded battery terminals can cause hard starting by adding resistance to the cranking circuit. Technician B says a battery should always be replaced when terminals are corroded. Who is correct?

• ATechnician A only
• BTechnician B only
• CBoth A and B
• DNeither A nor B

A cranking voltage test on a 24 V starting system shows battery voltage dropping to 16 V while cranking with a slow crank. The most likely cause is:

• ACharging system overcharging
• BToo high a CCA rating
• CWeak batteries or high resistance in the cranking circuit
• DAn open lighting fuse

In a series-parallel battery system used to crank a 24 V starter while running 12 V accessories, the series-parallel switch (SPS):

• AAlways keeps batteries in series
• BConnects batteries in series only during cranking, then returns them to parallel for 12 V…
• CDisconnects the alternator during cranking
• DConverts AC to DC for the accessories

A starter motor draws very high current but cranks slowly, and the battery is known good and fully charged. The next best test is to:

• AVoltage-drop test the starter feed and ground circuits while cranking
• BReplace the alternator
• CReplace the batteries
• DAdjust the destination sign

A clicking starter solenoid that does not engage the starter, with good battery voltage at the solenoid, most likely indicates:

• AA fully charged battery problem
• BAn overcharging alternator
• CWorn solenoid contacts or a faulty starter unable to carry full current
• DA blown headlight fuse

When connecting two batteries in series for 24 V, the correct connection is:

• APositive of one to positive of the other
• BPositive of one battery to negative of the other
• CNegative of one to negative of the other
• DAll four terminals tied together

A high voltage drop measured across a battery cable connection during cranking indicates:

• AThe cable is the correct size and clean
• BExcessive resistance at that connection that must be cleaned or repaired
• CThe alternator is overcharging
• DNormal operation for a transit bus

Before disconnecting transit bus batteries for service on a multiplexed bus, the technician should:

• ANote that volatile module memory and learned data may be lost and follow the proper power…
• BCrank the engine first
• CIncrease alternator output
• DDisconnect the destination sign only

CCA (cold cranking amps) on a heavy-duty battery is defined as the current the battery can deliver for 30 seconds at -18 C (0 F) while maintaining at least:

• A10.5 V for a 12 V battery
• B9.6 V for a 12 V battery
• C12.6 V for a 12 V battery
• D7.2 V for a 12 V battery