Hi guys,

I have a MK4 focus and about two weeks ago a message threw up saying key battery was low. I replaced it and my keyless entry was intermittently working which I thought was due to me not doing long journeys for a while. I just did a 140 mile round trip and it's now not working at all..any ideas what's wrong? Thanks

Hi Shane, Happy New Year.

So to answer the problem of why the keyless entry is not working. The problem is the SOC (State Of Charge) of your battery. You can go for a drive of a thousand miles and it will not guarantee that your battery will have reached the necessary level.

Your car is equipped with a smart charge system (but it's not as cleaver as it thinks it is) which means that it will only charge your battery to a maximum SOC of 80% (factory default for UK vehicles). Now at this time of year with headlights, wipers, heated seats, heated screens etc, etc, then the poor battery struggles to say charged. Once the SOC falls below 70% the the car stars to disable various equipment to save power, so first to be disabled is the heated front screen (after all why would you want to use that in the middle of winter ?). Now when the car is parked and it needs to save battery power then it turns off keyless entry. At first it just disables the two rear doors and the passenger door, but if further savings have to be made then it will eventually turn off keyless entry on all doors.

To fix the problem you need to put your battery on charge every 3 to 4 weeks. Yes it's a pain, but it's all in the name of allegedly reducing emissions and saving the dolphins.

The correct method to charge your battery is very important. Leave the battery connected on the car and connect a smart battery charger. The positive lead needs to be connected directly to the battery terminal. The negative lead must be connected to the vehicle main ground point on the chassis (near the battery). Do NOT connect the negative lead direct to the battery terminal otherwise the BMS (Battery Monitor System) will not know the battery has been charged.

Finally all this messing about can be avoided by using the software FORScan and using it to set the SOC of your car to 90 or even 95% (like mine) and your battery will get charged by the car and live happily ever after. The End ! 

Quote

I just did a 140 mile round trip

In my experience, even though a long trip will have charged the battery sufficiently, its not until its stood for a while (overnight?) that the systems recognise that the SOC is now sufficient to activate the various systems again.

3 hours ago, unofix said:

Hi Shane, Happy New Year.

So to answer the problem of why the keyless entry is not working. The problem is the SOC (State Of Charge) of your battery. You can go for a drive of a thousand miles and it will not guarantee that your battery will have reached the necessary level.

Your car is equipped with a smart charge system (but it's not as cleaver as it thinks it is) which means that it will only charge your battery to a maximum SOC of 80% (factory default for UK vehicles). Now at this time of year with headlights, wipers, heated seats, heated screens etc, etc, then the poor battery struggles to say charged. Once the SOC falls below 70% the the car stars to disable various equipment to save power, so first to be disabled is the heated front screen (after all why would you want to use that in the middle of winter ?). Now when the car is parked and it needs to save battery power then it turns off keyless entry. At first it just disables the two rear doors and the passenger door, but if further savings have to be made then it will eventually turn off keyless entry on all doors.

To fix the problem you need to put your battery on charge every 3 to 4 weeks. Yes it's a pain, but it's all in the name of allegedly reducing emissions and saving the dolphins.

The correct method to charge your battery is very important. Leave the battery connected on the car and connect a smart battery charger. The positive lead needs to be connected directly to the battery terminal. The negative lead must be connected to the vehicle main ground point on the chassis (near the battery). Do NOT connect the negative lead direct to the battery terminal otherwise the BMS (Battery Monitor System) will not know the battery has been charged.

Finally all this messing about can be avoided by using the software FORScan and using it to set the SOC of your car to 90 or even 95% (like mine) and your battery will get charged by the car and live happily ever after. The End ! 

How do I go about using the software?

Download the software FORScan from here :- https://forscan.org/download.html

You will also need a 'modified' ELM327 lead like this one:- https://tunnelrat-electronics.fwscart.com/USB_Modified_with_switch_ELM327/p4541936_17045457.aspx

There is a YouTube video that shows you how it's done.