A6 Electrical / Electronic Systems — practice test

High-yield A6 topics

The material that shows up year after year. If you're short on time, start here.

• Voltage drop testing under load. Know the limits cold: about 0.1V per wire or connection, roughly 0.2V across a switch or a ground path, about 0.5V total on the insulated side of the starter circuit. The whole test hinges on understanding that a bad connection only reveals itself when current is flowing - an unloaded circuit reads perfect right up until it fails.
• Series and parallel circuit math. They will hand you a diagram with values and make you compute. Adding resistance in parallel lowers total resistance and raises total current; adding it in series drops current and shifts the drops. Voltage drops in series add up to source voltage, and an open reads full source voltage across the break.
• Battery state of charge and testing. Open-circuit voltage: 12.6V is 100%, 12.4V is 75%, 12.2V is 50%, 12.0V is 25%. Remove surface charge before reading. Load test at half the CCA rating for 15 seconds and it must hold above 9.6V at 70F. Hydrometer: 1.265 corrected, and more than 0.050 variation between cells condemns it.
• Parasitic draw. Normal is roughly 20-50 mA once modules go to sleep, and sleep can take 30-45 minutes. Keep the vehicle asleep while testing, use a low-current clamp or an ammeter in series without breaking the connection, and know how to halve the fuse box to isolate the offending circuit.
• Starter and charging diagnosis by the numbers. Slow crank with high current draw points at mechanical drag or a shorted armature; slow crank with low current points at high resistance in cables or connections. Cranking voltage should stay above 9.6V. On the charging side, know AC ripple from a failed diode (over about 0.5V AC, or a scope pattern with a missing hump) and that output should land within about 10% of rated.
• CAN bus basics. High-speed CAN runs 500 kbps on a twisted pair with two 120 ohm terminators, so it reads about 60 ohms across pins 6 and 14 with the key off. CAN-H idles near 2.5V and pulls up toward 3.5V; CAN-L idles near 2.5V and pulls down toward 1.5V. A 120 ohm reading means an open terminator or a broken bus segment. U-codes usually mean lost communication, not a bad module.

Where techs lose points on A6

Good technicians miss these — not from lack of skill, but because the question is built to catch them.

• Ohming a cable instead of loading it. A DMM reads 0.0 ohms on a battery cable that is 90 percent corroded internally, because the meter pushes microamps through it. The look-alike answer is always 'check the cable for resistance with an ohmmeter.' The right answer is a voltage drop test with the circuit operating.
• Confusing an open with a short. A short to ground blows fuses. An open or high resistance gives you dim, slow, or dead - it does not blow a fuse. And voltage present at a dead component does not mean the feed is good; it usually means the ground is open, because the meter sees source voltage right across the break.
• The test light. It is the shop reflex and the wrong answer around modules, airbags, and low-current circuits, because it draws real current and can cook a driver. Never put an ohmmeter across an airbag squib either - that alone can deploy it. Also remember a 10 megohm DMM reads phantom voltage on an open circuit and will send you chasing a ghost.
• Feedback faults. Brake lights that flicker the taillights, or a turn signal that lights the marker lamp, is almost always a bad shared ground feeding backward through another bulb filament - not a bad switch and not a bad bulb. Same logic with LED conversions and hyper-flash: that is reduced load on the flasher, not a wiring fault.

A study plan that works for A6

Roughly two weeks of real preparation, in the order that actually builds on itself.

1. Days 1-4: Ohm's law and circuit math until it is reflex. Work series, parallel, and series-parallel problems with real numbers. Then drill voltage drop limits (0.1V wire, 0.2V switch or ground, 0.5V starter feed) and read actual OEM wiring diagrams - trace power from fuse to load to ground, out loud, on ten different circuits.
2. Days 5-8: Battery, starting, charging. Memorize the SOC voltage table and the half-CCA load test spec. Work the high-current-slow-crank versus low-current-slow-crank logic until you can explain it to somebody else. Add diode ripple, computer-controlled charging (PWM and LIN field control), and starter circuit voltage drop.
3. Days 9-11: Lighting, clusters, body electrical, networks. Cover ground faults and feedback, LED versus incandescent load, bulb handling, parasitic draw procedure, CAN 60/120 ohm terminator math, and U-code interpretation. Do not skip SRS safety rules - they are free points.
4. Days 12-14: Timed practice questions only, in Technician A / Technician B format. Read every statement as a standalone true/false before you pick. For each miss, write one sentence on why the wrong answer looked right - that page is what you review the morning of the test.

Sample A6 questions

Straight from the bank — answers highlighted, with the explanation underneath.