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Start-stop System Not Working

When the automatic start-stop no longer switches the engine off at lights, the most common reason is that the system has decided conditions are not right: a weak or wrong battery, high electrical load, cold engine or climate demands.

Normal risk

Not a safety issue. A start-stop that never works often points to a battery that needs testing.

Short answer · Why has my start-stop stopped working?

Start-stop only switches off the engine when many conditions are met: the battery is strong enough, the engine is warm, the cabin temperature is close to the set level, the steering is not turned and doors and belts are closed. An ageing battery is the most common reason it stops working. Some cars need the new battery registered after replacement.

On this page

Safe checks you can do

  1. Check the conditionsEngine warm, seat belt on, doors closed, AC not on maximum.
  2. Have the battery testedA weak battery is the main cause.
  3. Check if the battery was replacedStart-stop cars usually need an AGM or EFB battery and sometimes registration.

Questions that narrow it down

  1. Was the battery recently replaced?It may need registration or be the wrong type.
  2. Does it work in summer but not winter?Cold and heating demand.
  3. Is there a message on the dashboard?It may explain why.

Possible causes

Listed without ranking. Use the questions above to see which ones fit your car.

  1. Weak or ageing batteryMost common cause.
  2. Wrong battery typeNeeds AGM or EFB.
  3. Battery not registeredThe car does not trust its state.
  4. Climate or comfort demandNormal temporary behaviour.
  5. Sensor or switch faultBonnet, door or battery sensor.

Questions about Start-stop System Not Working

Is it bad to switch start-stop off?

No, but you lose its fuel saving in traffic.

What is battery registration?

A procedure that tells the car a new battery was fitted so it charges it correctly.