Why is my car's start-stop system not working?

A car’s start-stop button (keyless ignition).

My car has a start-stop system, which seems to activate less frequently these days.

When it used to activate more frequently, I noticed a small improvement in my car’s fuel economy.

Under what circumstances would the system not work?

As a fully automatic function, the start-stop system allows only one driver-input, which is to turn it off or deactivate it completely with a dashboard button that is provided on all cars with this feature.

At all other times, the feature is controlled by its electronic controller.

In normal operation, the system shuts off the engine whenever the car comes to a standstill (or in some cars, almost at a standstill).

However, this will occur only if the electronic controller has checked a number of parameters and confirmed that the start-stop function can be activated.

For example, the engine must be at its normal operating temperature, the interior climate has to have the suitable temperature and humidity, the battery’s condition is at an optimum voltage and the braking force at the instant the car is at a standstill should be enough.

All these “check boxes” must be ticked for the start-stop system to kick in.

For instance, if the car’s battery is approaching its end-of-life and the voltage is hence not up to the value recognised by the electronic controller as “okay” for start-stop operation, the said function will not be activated.

If you need to change the battery on a car with start-stop feature, make sure the correct type of battery (specified in the owner’s manual) is installed.

Batteries meant for start-stop systems are capable of sustaining voltage over a higher frequency of starts and are different from the regular lead-acid batteries.

Accessories such as powerful audio systems and certain in-car cameras may demand high enough power from the battery to cause the minimum voltage to be unsustainable for continuous start-stop function.

Also, on a very hot day, when the air-conditioning system is called upon to maintain a comfortable interior temperature for the occupants, the engine will not shut down, so as to keep the air-conditioning compressor running and ensure that the ventilation system can deliver cool air inside the cabin.