These instructions apply to the Audi A4 Mk5 (B9/8W) 2015-Present.
For other models, please choose your vehicle here.
Your Audi A4 (B9/8W, 2015–present) switches the engine off at a standstill to save fuel. When you’d rather it stayed running — heavy traffic, a hot day, or before any under-bonnet work — one button switches it off.
The engine going quiet the instant you stop is normal on the B9 A4 — it’s the start/stop system saving fuel, not a stall. It fires straight back up as you lift off the brake (automatic) or dip the clutch (manual). The “A”-in-arrow symbol in the driver display just means the system is armed. Plenty of owners leave it working; if you prefer a steadier feel in traffic, one press of the button turns it off for the drive.
How It Works on This Model
Start/stop only shuts the engine down when its conditions are satisfied. In broad terms the A4 wants the car fully at rest, a healthy 12 V battery, a warm engine, and the cabin close to its climate target. If the battery charge is low, the engine is still cold, the heater or air-conditioning is working hard, the steering is turned, or the car senses a slope, it simply keeps running. That is deliberate — the system only auto-stops when it’s sure it can restart cleanly, which is why the stop doesn’t always happen.
Before You Begin
- You can switch start/stop off with the engine already running — no need to stop.
- Locate the AⓇ button first so you can press it without looking.
- If you’re opening the bonnet, switch it off so the engine can’t restart on its own.
- The setting lasts for this drive only, so press it early in the journey.
Turning Start/Stop Off
- Find the AⓇ button (an “A” circled by an arrow), usually near the gear selector or the dashboard switches.
- Press it once; the indicator confirms the system is off and the engine stays running at stops.
Why It’s On Again Next Time
The A4 switches start/stop back on at every ignition cycle — there’s no permanent off from the factory. Tap the button once at the start of each drive if you don’t want it.
If the Engine Won’t Stop
If start/stop rarely or never triggers, it’s almost always an inhibit condition rather than a fault. On the A4 the usual culprits are:
- A tired or under-charged 12 V battery — by far the most common reason, and worth checking first.
- The engine hasn’t warmed up yet on a short or cold-weather drive.
- The climate system is working hard to heat or cool the cabin.
- You’re stopped on a gradient, or the car isn’t fully at rest.
- The steering is turned, the demister is on, or the bonnet is open.
- On mild-hybrid versions the engine may also coast off while moving — that’s separate, normal behaviour.
Reasons to Switch It Off
- Engine-bay jobs — no surprise restart.
- Heavy traffic — no constant cycling.
- Hot or cold extremes — steadier climate output.
The system also declines to stop on its own when the battery is low, the cabin still needs heating/cooling, or you’re on a slope — all normal. Mild-hybrid A4 versions also coast with the engine off while moving as part of normal operation.
After the Reset
With start/stop off, the indicator shows the system disabled and the engine keeps running at every stop for the rest of the journey. When you next start the car it will be armed again automatically — that’s expected. The effect on overall fuel economy is small, so switching it off is about driving comfort rather than any mechanical concern.
Frequently Asked Questions
How do I switch off auto stop/start on an Audi A4?
Press the AⓇ button, usually near the gear selector or among the dashboard switches. The indicator confirms the system is off and the engine will then stay running at stops. You can do this at any time with the engine running; there’s no need to be stationary first.
Can it stay off for good?
No — the A4 re-arms start/stop at every ignition cycle, and there’s no factory option to keep it permanently off. Press the button once at the start of each drive if you’d rather not use it. It becomes second nature after a few journeys.
Why did it switch itself back on?
Cycling the ignition re-enables it — it hasn’t turned itself back on mid-drive. If it seems to reappear during a single journey, double-check the “off” indicator was actually lit when you pressed the button, as a brief press can be missed.
Why won’t the engine cut at junctions?
An inhibit condition is being met. Common ones are a cold engine, a battery that isn’t fully charged, the heater or air-conditioning working hard, or a gradient under the wheels. The A4 only auto-stops when a smooth restart is assured, so this is normal, expected behaviour.
Does start/stop harm the engine or starter?
No. The B9 A4 uses a heavy-duty starter and an AGM or EFB battery built for frequent cycling, and the engine only stops once warm. There’s no meaningful extra wear in normal use, so choosing to disable it is a comfort preference, not a mechanical necessity.
My start/stop symbol is amber — is that a fault?
The plain white/green “A”-in-arrow is just the status light. A separate amber start/stop or battery warning points to a fault, most often a weak 12 V battery that can no longer support auto-restarts. Have the battery tested before assuming anything more serious.
If a start/stop fault symbol shows rather than the normal one, look it up on autodtcs.com — usually a weak 12 V battery. See our A4 battery guide.
Independent guide — not affiliated with Audi. Always follow your official service manual and safety precautions. Read our full disclaimer.