Battery and electrics
Why is stop-start not working?
Almost always it is because a condition is not met: the battery is not charged enough, the engine or cabin is not at the right temperature, the climate control is working hard or a particulate filter regeneration is under way. If stop-start never works for weeks, the most common cause is an aging battery or one that was not registered after replacement.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What conditions does it need?
A sufficiently charged battery, a warm engine, the climate control not asking for much, the seat belt fastened, doors and hood closed, the car stopped and, on some, the wheels straight or no steep slope.
If any is missing, the car does not stop the engine, and that is normal. Many clusters show it with a crossed-out stop-start symbol or a message.
What does the battery have to do with it?
The system monitors its condition with a sensor. As the battery ages, the control unit avoids stopping the engine to make sure of the next start.
If you replaced the battery with a different type or did not register it on cars that require it, stop-start may stop working.
When is it a fault?
If it never works, with a healthy battery and a warm engine, or if the cluster shows a system warning, read the codes: it may be the battery sensor, a hood or clutch sensor, or another control unit.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
Related symptoms
- Battery warning light on: what it means and what to do
- Particulate filter regenerating too often: causes
- Car battery keeps going flat: causes and what to do
Learn more
See what your car is saying
With the ECO-LITE, your workshop can check remotely the battery and the faults that block stop-start.
Presale price: €129 · US$129
Frequently asked questions
Is it bad to switch stop-start off?
It does not harm the car; you only lose the fuel savings at stops.
Does stop-start wear out the battery?
It is designed for it with EFB or AGM batteries. With the right battery, it does no more harm than expected.
Why doesn't it stop the engine in summer?
If the air conditioning needs a lot of power to cool, the car prefers not to stop the engine.