New Car Battery Fitted now Car not Locking

[DWM]

Hi, hope someone can help, my sons 2018 MK8 Fiesta had a dying car battery so we changed ourselves. I read on a forum elsewhere that you should reset the cars BMS so I did this with FORScan all seemed okay until we tried to lock the car and nothing. The car starts and we changed the key fob battery just in case. You can lock the car from inside using the rocker switch on the driver's door and we checked the fuses behind the glove box just in case. Any ideas please?

 

[econoboxrocks]

Beats me.

 

[Handy Andy]

In the USA we have a battery minder a relay-cutout system that is thru the Body Control Module - so your mileage may vary...

IN your situation...see if what has been discussed elsewhere can apply by watching this vid's techniques helps...

This Video link might be able to help explain the process

The Battery Cables should be cleaned and includes the Ground cables two points the Battery side and the Vehicle side - to ensure the sensitivity of and its ability to detect threshold changes - the BMS needs to be reset or "Zeroed out".

What I would do first is a Pull the Battery Cables and jumper short them together for 10 minutes OFF THE BATTERY - then reattach them back onto the battery - and see if the Keyfob can reset and unlock the doors.

You have to get the unlock and relock sequence done - then worry about a BMS reset.

The BMS stuff is pretty simple
(Presumes you have Push To Start - not Key In ignition)

1. Engine On not running
2. Pull Left (Hi-Lo-Flash_to_pass) headlight lever back towards you and release (blink your Hi-Beams) 5 times (timing of this will need to be figured out by you so you can time the pull interval)
3. Press Brake pedal down enough to light your rear Brake lights - then release - 3 times.
4. Wait - paying attention to the BATTERY icon (also identified in your O/M as Ignition) should Blink 3x in succession then go off for a moment then back on.

You'll have to have the vehicle recognize the Keyfob, then it can work - else it's locked out. The BMS kind of resets the system but it then protects itself, in ST-line and ST cars this may require your OEM keys until an OEM key (your Administration KEY in MY KEY) is present.

• Remember - FORscan WRITES to an address whether it is the RIGHT one or not - so the right version of FORscan updated for the ST line and year is highly recommended - even if it's only a trial.

So, the ADMIN (Administration or unprogrammed) key is needed to recognize the key - else you can start with the physical key in the ignition or unlock with the key, but no way to turn off the alarm going on.

So, if you have the original ADMIN key - that should unlock the doors and be recognized - but to fix the key not recognized - requires an ADMIN key (one of the OEM ones you got during the purchase) present as a pair - so the system then can recognize the two keys validated as one is a Real owner and one extra. This is all done AFTER you've done the Battery Cable pull - reset out for 10 min then reattach moment.

Hope the FORscan moment did not destroy data needed to get your car to start and run again.

 

[DWM]

Thank you very much for taking time to respond with such detail, I was heading for the disconnect the battery option as my first port of call but the fault decided to fix itself after the car was driven for a short trip. Very weird. It's a ST Line with Push Start.