Charging is the smallest area on A6, 5 of the 50 scored questions, and it reuses the meter skills from the rest of the test: output voltage and current, AC ripple, and voltage drop in the charge circuit.
Pulleys, tensioners and drive belts: inspect, replace, adjust, check alignment.
Voltage output and current output tests.
Generator control: sensors, regulators and modules.
Charging circuit voltage drop, connectors, terminals and wires.
Generator (alternator) removal and replacement.
Three tests, in order
Voltage output. Engine running, voltage at the battery against spec. Where a module controls the generator, it sets the target and can lower it when the battery is full, so compare with the commanded value on the scan tool, not a fixed number.
Current output. Load the system and read amps with a clamp, against the generator's rating. Voltage that looks fine at idle with no load can hide a generator that can't deliver current.
Ripple and voltage drop. AC voltage on the generator output points to a failed diode or stator winding. Voltage drop between the generator output and the battery positive, then between the generator case and the battery negative, shows charge-circuit resistance. The first A6 sample in the 2026 guide puts a meter across exactly that positive-side path.
When the voltage is wrong
No charge. Check the drive belt, the field control or module command, and the output connection before condemning the generator.
Low charge. A slipping belt, high resistance in the charge circuit, a failed diode or stator winding, or a module commanding low output.
Overcharge. The regulator or its control: a failed regulator, a wrong command, or a sense or ground circuit that makes the regulator read low.
Trap: a fusible link replaced with wire
A fusible link in the charge circuit replaced with ordinary wire of system size leaves the circuit unprotected. It does not make the battery overcharge: regulation happens elsewhere. The 2026 guide uses this pair of Technician A/B statements as a sample.
12 charging system questions
0 of 12 answered · 0 correct
Question 1 of 12 · Charging System Diagnosis and Repair · 10%Not answered
A PCM-controlled alternator is overcharging at 15.5 V. Scan tool data shows commanded field duty of 40%, PCM battery sense voltage of 12.8 V, while actual battery voltage is 15.5 V. What is the most likely fault?
Explanation
Correct: The PCM sees 12.8 V while the battery is at 15.5 V, so a drop in the sense wire makes it drive the field harder.
Incorrect: The field command matches the false 12.8 V the PCM is shown, so the regulator is obeying.
Incorrect: A shorted field winding cannot explain why the sensed voltage disagrees with the battery.
Incorrect: A resistive output cable lowers battery voltage instead of pushing it to 15.5 V.
Incorrect: The PCM is acting logically on a low sensed voltage; the input is what is wrong.
Question 2 of 12 · Charging System Diagnosis and Repair · 10%Not answered
With the engine running, an AC voltage of 1.1 VAC is measured across the battery terminals. The manufacturer's limit is 0.5 VAC. What does this indicate?
Explanation
Incorrect: The battery smooths ripple; a weak one does not generate AC voltage.
Incorrect: 1.1 VAC is more than double the 0.5 VAC limit, so it is not normal.
Correct: Excess AC at the battery means the rectifier is letting AC through, from a failed diode or stator winding.
Incorrect: A regulator fault shows up as wrong DC voltage, not AC ripple.
Incorrect: A slipping belt lowers output and may squeal, but it does not put AC on the system.
Question 3 of 12 · Charging System Diagnosis and Repair · 10%Not answered
A technician tests a charging system using a carbon pile load tester. The alternator is rated for a maximum output of 140 amps. During the test, the maximum measured output is 105 amps. If the manufacturer's specification requires at least 80% of rated capacity, what is the conclusion?
Explanation
Incorrect: 15.0 A is an arithmetic slip; 112 A minus 105 A is 7.0 A.
Correct: 80 % of 140 A is 112 A, so 105 A falls 7.0 A short.
Incorrect: 105 A is below the 112 A requirement, so the alternator does not pass.
Incorrect: The output is under the required 112 A, so it cannot pass by any margin.
Incorrect: 35.0 A is the gap to the full 140 A rating, not to the 80 % requirement.
Question 4 of 12 · Charging System Diagnosis and Repair · 10%Not answered
With the engine running, an alternator B+ output terminal measures 14.5 V and the battery positive terminal measures 13.8 V while the charging current is 50 A. What is the resistance of the alternator-to-battery cable, and is it acceptable if the maximum allowable resistance is 0.005 ohm?
Explanation
Incorrect: 0.00014 Ω misplaces the decimal; 0.7 ÷ 50 is 0.014.
Incorrect: 0.014 Ω is the right value, but it exceeds the 0.005 Ω limit, so it is not acceptable.
Incorrect: 0.007 Ω halves the real value, as if the drop were 0.35 V.
Correct: 0.7 V ÷ 50 A = 0.014 Ω, nearly three times the 0.005 Ω maximum.
Incorrect: 0.07 Ω is ten times too high for a 0.7 V drop at 50 A.
Question 5 of 12 · Charging System Diagnosis and Repair · 10%Not answered
A vehicle's charging system is being evaluated on a cold morning (20°F). The battery is at a 75% state of charge. What is the expected behavior of the alternator's target voltage output compared to a standard 70°F day with a fully charged battery?
Explanation
Correct: Regulators raise the setpoint in the cold, and a partly discharged battery adds to the demand for charge.
Incorrect: Ripple depends on diode and stator condition, not on temperature or state of charge.
Incorrect: A lower setpoint is the hot-weather adjustment; cold raises it.
Incorrect: A cold, partly discharged battery calls for more charging, not none.
Incorrect: Temperature compensation means the setpoint does move with battery temperature.
Question 6 of 12 · Charging System Diagnosis and Repair · 10%Not answered
With the engine running at 2000 RPM and all electrical loads turned on (high beams, blower motor, rear defroster), a technician measures only 12.5 volts at the battery. What is the most likely condition?
Explanation
Incorrect: One heavy load cannot drag a healthy alternator below battery voltage at 2,000 rpm.
Incorrect: A low battery accepts more charge, but the alternator should still lift system voltage above 13 V.
Correct: A working system holds well above 12.6 V at 2,000 rpm, so 12.5 V means the alternator is not keeping up.
Incorrect: A healthy system holds about 13.5 V or more even with these loads, so 12.5 V is not normal.
Incorrect: An open grid line reduces the electrical load, so it cannot pull charging voltage down.
Question 7 of 12 · Charging System Diagnosis and Repair · 10%Not answered
During a charging system test, the alternator output measures 15.9 volts at idle. Which of these is the most likely cause?
Explanation
Incorrect: A slipping belt lowers output, so it causes undercharging, not 15.9 V.
Incorrect: A shorted temperature sensor reads as a hot battery, which lowers the target voltage.
Correct: 15.9 V at idle is above the normal 13.5–14.5 V range, and limiting voltage is the regulator's job.
Incorrect: An open field winding stops the alternator from charging at all.
Question 8 of 12 · Charging System Diagnosis and Repair · 10%Not answered
What is the normal charging system voltage range at idle with all accessories off?
Explanation
Incorrect: 15–16 V is overcharging, which boils the battery and stresses electronics.
Correct: A working charging system holds about 13.5–14.5 V, enough to charge a 12.6 V battery without overcharging it.
Incorrect: 11.8–12.6 V is resting battery voltage, meaning no charging is happening.
Incorrect: 10.5–11.5 V is a discharged battery, far below any charging voltage.
Question 9 of 12 · Charging System Diagnosis and Repair · 10%Not answered
What causes alternator belt squeal during operation?
Explanation
Correct: A loose or wrongly tensioned belt slips on the pulley and squeals, especially under heavy charging load.
Incorrect: A regulator failure changes output voltage; it does not make the belt slip.
Incorrect: A blown fuse can stop charging but makes no noise at the belt.
Incorrect: A low battery adds charging load, but a correctly tensioned belt carries it without squealing.
Question 10 of 12 · Charging System Diagnosis and Repair · 10%Not answered
What causes excessive alternator noise?
Explanation
Correct: Worn alternator bearings grind or growl, and the noise rises with engine speed.
Incorrect: A failed regulator changes output voltage but makes no mechanical noise.
Incorrect: An open field stops output, which if anything makes the alternator quieter.
Incorrect: A weak battery adds charging load but causes no mechanical noise.
Question 11 of 12 · Charging System Diagnosis and Repair · 10%Not answered
What test should be performed first when diagnosing a charging system complaint?
Explanation
Correct: Battery condition and state of charge come first, because a bad battery skews every charging test.
Incorrect: A starter test belongs to a cranking complaint, not a charging one.
Incorrect: Fuses and fusible links are checked during diagnosis, after the battery is known to be good.
Incorrect: Removing the alternator before testing skips the diagnosis entirely.
Question 12 of 12 · Charging System Diagnosis and Repair · 10%Not answered
Which alternator component converts AC current to DC current?
Explanation
Incorrect: The stator is where the AC is produced, so it is the source, not the converter.
Incorrect: The regulator controls field current to set output voltage; it does not rectify.
Incorrect: The rotor is the spinning electromagnet that makes the field; it does not convert AC to DC.
Correct: The rectifier's diodes turn the stator's AC into the DC the vehicle uses.
With the engine running and the system loaded, measure between the generator output terminal and the battery positive post, then between the generator case and the battery negative post. Each reading is the loss in that side of the circuit; compare it with the maker's limit.
What does AC ripple on an alternator mean?
AC voltage riding on the DC output. Above the maker's limit, it points to a failed diode or stator winding.
How many charging questions are on A6?
5 of the 50 scored questions, 10%, the smallest of the five areas.