ASE A6 Electrical/Electronic Systems Study Guide — What to Study and How to Pass

A6 is the test that separates the electrically-minded techs from the rest. If you understand how electrons flow and why circuits behave the way they do, this test is straightforward. If you memorize procedures without understanding the theory, you will struggle.

The good news: electrical theory is a small set of rules that apply to EVERY question. Learn the rules, and you can reason through any question even if you have never seen that specific scenario before.

Test Breakdown

• General Electrical/Electronic System Diagnosis: ~13 questions (25%)
• Battery Diagnosis and Service: ~5 questions (10%)
• Starting System: ~5 questions (10%)
• Charging System: ~5 questions (10%)
• Lighting, Gauges, and Accessories: ~13 questions (25%)
• Body Electrical / Network Systems: ~9 questions (20%)

General Electrical Diagnosis (25%)

What to Know

• Ohm's Law: V = I x R. Voltage equals current times resistance. If resistance increases in a circuit, current decreases. If resistance decreases, current increases. Know how to apply this to real scenarios — a corroded connector adds resistance, which reduces current flow to the component, which makes it work weak or not at all.
• Series vs. parallel circuits: In series, current is the same everywhere but voltage drops across each load. In parallel, voltage is the same across each branch but current divides. Most vehicle circuits are parallel — each load connects between power and ground independently.
• Voltage drop testing: The most important electrical test you can perform. Voltage drop measures resistance UNDER LOAD — something a static resistance test cannot do. More than 0.5V drop on a power side, more than 0.3V drop on a ground side = excessive resistance. Read the voltage drop article for the full procedure.
• Wiring diagram interpretation: Know standard electrical symbols — battery, fuse, relay, switch, motor, ground, connector. Know how to trace a circuit from power source through fuse, switch, load, and ground. Read the wiring diagrams article.
• Short circuits vs. open circuits: A short circuit creates an unintended low-resistance path — blows fuses, overheats wires. An open circuit breaks the current path — component does not work at all. Know how to test for each.
• Parasitic draw testing: How to connect an ammeter in series with the battery to measure key-off current draw. Normal is under 50mA after all modules sleep. Know that opening a door or connecting a meter can wake modules — wait for sleep timer.

Battery Diagnosis and Service (10%)

What to Know

• Battery types: Flooded lead-acid, AGM (Absorbed Glass Mat), gel. AGM batteries require AGM-specific charging settings — overcharging damages the glass mat separators.
• Battery testing: Open circuit voltage (12.6V = full charge, 12.4V = 75%, 12.2V = 50%). Load testing — apply a load equal to half the CCA rating for 15 seconds, voltage should not drop below 9.6V at 70F. Conductance testing with an electronic tester.
• Battery charging: Slow charge (2-10 amps) vs. fast charge (40+ amps). Never fast-charge an AGM battery. Temperature affects charging — cold batteries accept charge slower.
• Jump starting: Connect positive to positive first, then negative to engine block (not battery terminal) on the dead vehicle — prevents spark at the battery that could ignite hydrogen gas.

Starting System Diagnosis (10%)

What to Know

• Starter circuit: Battery → cable → solenoid → motor → ground. A voltage drop test on each segment identifies the weak link. More than 0.5V drop on any single connection under cranking load is excessive.
• Starter draw test: A healthy starter draws 150-250 amps on a 4-cylinder, 200-350 amps on a V8. Excessive draw indicates a mechanical problem — bad bearings, tight engine, hydrolocked cylinder.
• No-crank diagnosis: Battery voltage under load, solenoid click vs. no click, voltage at solenoid S terminal. A single click with voltage drop at the solenoid = bad solenoid contacts. Multiple rapid clicks = insufficient battery voltage or bad cable connections.

Charging System Diagnosis (10%)

What to Know

• Alternator output: Should produce 13.5-14.5V at the battery with the engine running and loads on. Below 13.5V = undercharging. Above 15V = overcharging (bad voltage regulator).
• AC ripple: A diode rectifier converts AC to DC inside the alternator. A failed diode lets AC pass through. Measure AC voltage at the battery — more than 0.5V AC with the engine running indicates a bad diode. A scope shows the ripple pattern clearly.
• Drive belt inspection: Cracking, glazing, rib wear. A slipping belt causes intermittent undercharging, especially under high electrical load.
• Voltage regulator: Internal (inside alternator) or external. Regulates field current to maintain target voltage. Over-regulation = low voltage. Under-regulation = high voltage and boiled batteries.

Lighting and Electrical Accessories (25%)

This is a big section — 13 questions. It covers everything from headlights to power windows to gauges.

What to Know

• Headlight circuits: Multifunction switch operation, dimmer function, daytime running lights. HID and LED headlight systems — ballast operation, driver module diagnosis.
• Turn signal and hazard: Flasher module operation. If turn signals work but hazards do not (or vice versa), the problem is in the switch or flasher — they use separate circuits on most vehicles.
• Gauge operation: Sending unit (variable resistance) changes gauge reading. A grounded sender wire pegs the gauge to one end. An open sender wire pegs it to the other end. Know which direction for fuel, temperature, and oil pressure.
• Power windows/locks/mirrors: Master switch vs. individual switch diagnosis. A window that works from the master switch but not the door switch = bad door switch. A window that does not work from either = motor, regulator, or circuit.
• Wiper/washer system: Wiper motor park circuit — the motor runs to the park position after you turn it off. A failed park switch causes the wipers to stop mid-sweep.

Body Electrical and Network (20%)

What to Know

• CAN bus basics: Two-wire differential communication. CAN High idles at 2.5V, pulses to 3.5V. CAN Low idles at 2.5V, pulses to 1.5V. Termination resistors at each end of the bus (120 ohms each, 60 ohms measured at the DLC). Read the CAN bus diagnostics article.
• LIN bus: Single-wire, master-slave network for body accessories (mirrors, seats, windows). Lower speed than CAN.
• Module communication: Gateway modules route data between networks. A failed gateway can prevent communication between entire networks. U-codes indicate communication faults.
• Immobilizer/anti-theft: Transponder key communication with the immobilizer module. If the module cannot verify the key, it disables fuel injection and/or starter operation.
• Multiplexing: Multiple signals sharing one wire by time-division. Reduces wiring but means a single wire failure affects multiple systems. Common symptom: multiple unrelated systems fail simultaneously = shared wiring or communication issue.

Study Tips for A6

• Start with Ohm's Law. If you do not understand V = I x R and how voltage, current, and resistance interact, nothing else on this test will make sense. Spend time here first.
• Practice reading wiring diagrams. ASE includes diagram-based questions. Being able to trace a circuit from source to ground through all components is essential.
• Know voltage drop testing cold. Multiple questions will test this concept directly or indirectly. It is the single most tested diagnostic technique on A6.
• CAN bus is growing. Newer versions of A6 include more network communication questions. Do not skip this section.