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sean, Technician
Category: Car
Satisfied Customers: 3105
Experience:  UK based Ford Master Technician. Technician since 1984.
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Over the last year my 2011 1.6 zetec TDCI has lost its stop/start

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Over the last year my 2011 1.6 zetec TDCI has lost it's stop/start ability and the remote locking has been sluggish. My local dealer says it's because my battery is only reading 69.5 instead of 72(whatever that means!).They "boosted" it and everything was perfect for about a week then it was back to square 1. I took it back again as it's nearly out of warranty. Same story."there's nothing wrong with the car you're not giving it enough long runs!" My running is no different from before and I can't believe that the main economy feature of the car would be inoperative because the battery wasn't at peak output. I would also imagine that most Focus owners will do as many miles shopping as going from Glasgow to London! Any helpful idea? Donald Milne

Hello, I hope the following is of assistance.

The readings the dealer referred to are the state of charge of the battery, if the state of charge is below 72% then the start/stop feature is disabled to prevent any risk of a non start situation.

The battery is checked using a battery monitoring sensor (BMS) this works as follows.

The sensor measures temperature, voltage and current throughput of the battery.
It uses this information to calculate the battery SoC (State of Charge) and SoH
(State of Health). To function with high accuracy, the BMS must be recalibrated
at regular intervals. A recalibration occurs during a rest period when the
battery quiescent current is less than 100mA. This rest period must last for at
least three hours. The longer the rest period, the greater the accuracy. The
time frame in which a recalibration must take place is seven days. If the system
has been unable to carry out a recalibration within seven days, the SOC accuracy
cannot be guaranteed. This will result in the Start/Stop and SRC systems being
deactivated. These systems will also be disabled if the sensor detects the
battery is reaching its end of life, low state of charge or health.

Any charging of the battery needs to be done correctly otherwise the SOC and SOH will be calculated incorrectly and the start/stop will not work.

There are many other factors that will affect the start/stop function, engine temperature, air temperature, temperature inside the car to name a few.

To be honest 90% of start/stop faults I see are due to a battery fault it may be worth asking the dealer to check the battery and ask to see the start/stop battery test done if possible, this way you can see the results for yourself.

I hope this helps but if I can advise further let me know and I'll reply as soon as I'm able to.

Best wishes,


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