These instructions apply to the MG HS Mk1 2019-present.
For other models, please choose your vehicle here.
Your MG HS (2019–present) with stop/start shuts the engine off at a standstill to save fuel and trim emissions. When you’d rather keep it running — crawling traffic, a hot day, or before any under-bonnet work — one button switches it off. The circled-‘A’ light on the cluster simply reports the system’s state; it is a normal feature, not a fault, and seeing it flick between amber and green through a drive is exactly how it’s meant to behave.
How Stop/Start Works on the HS
When you come to rest and hold the brake in an automatic — or sit in neutral with the clutch up in a manual — the HS cuts the engine and keeps the cabin, lights and audio alive on the 12 V battery. Lift off the brake or dip the clutch and it fires straight back. The car only allows a stop when a set of inhibit conditions are met: the battery must hold enough charge, the engine and catalyst need to be warm, and the cabin temperature has to be close to what you’ve asked the climate system for. Miss any of those and the engine simply keeps idling.
First, a Few Checks
- You only need the ignition on — no tools, and the engine can be running or off.
- Decide first whether you want it off just for this journey or every journey; the HS has no permanent off, so plan to repeat it.
- For under-bonnet work, switch stop/start off and the ignition fully off so there’s no chance of an auto-restart.
- Note where the button sits before you set off, so you’re not hunting for it in traffic.
Turning Stop/Start Off
- Locate the stop/start button — an A inside a circular arrow — on the dash or centre console.
- Press it once; the indicator confirms the system is off and the engine stays running at stops.
If your HS routes it through the touchscreen, look under Vehicle / Settings for the engine auto-stop (stop-start) toggle.
Why It’s On Again Next Time
The HS switches stop/start back on at every ignition cycle — there’s no permanent off. Press the button at the start of each drive if you don’t want it.
If the Engine Won’t Stop — or Won’t Stay Off
If pressing the button seems to do nothing, or the engine keeps running when you expect a stop, run through these before assuming a fault:
- Weak or cold 12 V battery. This is the most common reason the engine won’t auto-stop; the HS holds the engine running to protect and charge a tired battery, especially on short trips or cold mornings.
- Cabin not yet at temperature. On a very hot or cold day the climate system vetoes stops until the interior settles.
- Cold engine. Straight after a cold start the engine stays running until it’s warmed through.
- Brake not held firmly (autos) or the car isn’t fully at rest — a gentle roll keeps it running.
- On a gradient, the HS may skip the stop for hill-hold reasons.
- You’ve just pressed the button — if the indicator shows off, that’s working as intended, not a fault.
- If a warning symbol stays lit with the system genuinely disabled, have the 12 V battery load-tested before anything more involved.
Once It’s Done
With stop/start switched off, the button’s indicator stays lit and the engine idles normally at every stop for the rest of the journey. Next time you start the car the system re-arms itself and the light returns to its ready state — press the button again if you want it off. Nothing is stored, and no warning should linger once you cycle the ignition.
Frequently Asked Questions
How do I turn off auto stop/start on an MG HS?
Press the circled-‘A’ button on the dash or console once; the indicator confirms the engine will now idle at stops instead of cutting out. If your car doesn’t have the physical button, open the touchscreen Vehicle or Settings menu and switch the engine auto-stop (stop-start) toggle off. Either way it only lasts for the current drive.
Can I disable it permanently?
No — the HS re-enables stop/start automatically every time you start the car, and there’s no factory setting to keep it off for good. The simplest habit is to press the button at the start of any journey where you don’t want the engine cutting out, such as slow traffic or a hot day when you want steady climate output.
Why didn’t the engine stop today?
A stop is only allowed when several conditions line up: enough 12 V battery charge, a warm engine, and a cabin close to the temperature you’ve set. Low charge, a cold engine, strong heating or cooling demand, or sitting on a slope will all keep the engine running by design. This is normal protective behaviour, not a malfunction.
Is it bad to leave it on?
No — the HS is engineered for constant stop/start use, with a heavier-duty starter and a battery suited to frequent cycling. The one thing that makes it feel erratic is a tired 12 V battery, which reduces how often the engine is allowed to stop. If it’s stopping far less than it used to, the battery is the first thing worth checking.
Does stop/start drain or wear the battery?
Not in normal use — the system constantly monitors charge and won’t auto-stop if the battery can’t comfortably support it, and it keeps the engine running to recharge when needed. Over years, an ageing battery will make stops rarer. Fitting the correct replacement type when the time comes keeps stop/start working as designed.
Will turning it off affect fuel economy?
Slightly — stop/start exists to save fuel during idling in traffic, so disabling it means the engine burns a little more when stationary. For a single drive the difference is small, and many owners accept it for smoother restarts in heavy traffic or steadier air-conditioning on a hot day. Leave it on for open-road driving where it makes almost no difference anyway.
If a stop/start fault shows, it usually points to the 12 V battery — see our HS battery guide, or look the code up on autodtcs.com.
Independent guide — not affiliated with MG. Always follow your official service manual and safety precautions. Read our full disclaimer.