These instructions apply to the Audi A3 Mk4 (8Y) 2020-Present.
For other models, please choose your vehicle here.
The Audi A3 Mk4 (8Y, 2020–present) has an automatic engine start/stop system that switches the engine off at a standstill to save fuel. If you’d rather keep it running — in traffic, on a hot day, or before working in the engine bay — you switch it off with one button. This is a normal comfort and economy feature, not a fault; the indicator that appears when the engine cuts out simply shows the system is working as designed.
How Start/Stop Works on the A3
When you brake to a standstill (automatic) or stop, select neutral and release the clutch (manual), the engine shuts off; lift the brake or dip the clutch and it restarts. Before it will let the engine sleep the A3 checks a set of conditions: the 12 V or AGM battery must hold enough charge, the engine must be warm, cabin climate demand must be modest, and the car must be genuinely stationary with the brake held firmly. Fail any one of these and the engine keeps idling — the system never risks a stop it can’t cleanly recover.
Before You Start
- Have the engine running — you set this while stationary or moving, not with the ignition off.
- The choice applies to the current journey only; the setting is not stored.
- For engine-bay work, switch start/stop off first, then turn the ignition fully off to prevent any automatic restart.
- If you want the engine to actually auto-stop, let it warm up first — it stays out while cold.
How to Turn Off Start/Stop
- Find the AⓇ (A with a circular arrow) button near the gear selector or the dashboard switch bank.
- Press it once — the indicator shows the system is off, and the engine will keep running when you stop.
It Resets Every Drive
Like nearly every car with this feature, the A3 re-enables start/stop each time you switch the ignition off and on. There’s no permanent factory ‘off’ — press the button once per journey if you don’t want it.
Why Switch It Off?
- Before engine-bay work — stops an unexpected restart.
- Stop-go traffic — avoids constant restarts.
- Maximum cabin cooling/heating on extreme days.
On mild-hybrid versions the engine also restarts very smoothly and may “coast” with the engine off while moving — that’s the MHEV system working, not a fault. The system also skips the stop when the battery is low or climate demand is high.
If the Engine Won’t Auto-Stop
If you’ve left start/stop enabled but the engine keeps idling at every halt, check these before assuming a fault:
- Cold engine — the most common reason. The system stays out until the engine reaches normal operating temperature, so it rarely stops on the first mile or two from cold.
- Weak 12 V / AGM battery — an aged or under-charged battery causes the A3 to hold the engine running to protect starting. A charge or a battery test often restores normal behaviour.
- Recent battery disconnect — after a battery change or reconnection the system may sit out for several longer drives while it relearns the battery’s state of charge.
- Strong climate demand — hard heating, cooling, or windscreen demist keeps the engine running to hold cabin comfort.
- Not fully stopped — creeping forward, a light brake press, or the wheel turned at a junction can all hold the engine on.
- Gradient — on a noticeable slope the system may decline to stop so the car doesn’t roll.
- Seatbelt or door open — if the driver’s belt is unclipped or a door is ajar, the A3 keeps the engine running for safety.
What to Expect After
Once you’ve pressed the button the indicator stays lit and the engine idles normally at every stop for the rest of that drive. Turn the ignition off and back on and start/stop quietly returns to its default enabled state — there is no warning and nothing is wrong; the A3 simply prefers the fuel-saving mode each time you start.
Frequently Asked Questions
How do I turn off auto stop/start on an Audi A3?
Press the AⓇ button near the gear selector; the indicator confirms it’s off. The engine will then idle normally at every stop for the rest of that journey. You need to press it again after your next ignition cycle, because the setting is not retained between starts.
Can I disable it permanently?
No. It resets to on at every ignition cycle, so press the button each drive if you prefer it off. There is no factory menu option to make the “off” state permanent — that behaviour is deliberate and shared by almost every car fitted with automatic start/stop.
Why did stop/start come back on?
Switching the ignition off and on re-enables it automatically. The A3 always starts each journey with the fuel-saving mode active, regardless of how you left it on the previous drive, so a return to “on” after a restart is normal and not a sign of any fault.
Why won’t the engine stop sometimes even with start/stop on?
A low battery, high climate demand, or a gradient will hold the engine running — that’s by design. A cold engine, the steering being turned, or not coming to a complete stop will do the same. These are all inhibit conditions the A3 checks before it allows an engine stop.
What is the coasting feeling on the mild-hybrid A3?
On MHEV versions the A3 can switch the engine off while the car is still rolling and coast to save fuel, restarting seamlessly when you need power again. It feels like a brief lull in engine noise rather than a stall, and is a normal part of how the mild-hybrid system operates.
Is a start/stop warning light the same as the normal indicator?
No. The normal indicator lights only while the engine is asleep and clears as it restarts. A steady amber start/stop warning instead signals a fault — most often a tired 12 V battery — and is worth investigating rather than ignoring, since the system will stay disabled until it clears.
If a start/stop fault light shows instead of the normal indicator, look it up on autodtcs.com — a tired 12 V battery is the usual cause. See our A3 battery guide.
Independent guide — not affiliated with Audi. Always follow your official service manual and safety precautions. Read our full disclaimer.