FORScan forum

Component Description

Battery Monitoring Sensor

NOTE: Unless the battery is being replaced, DO NOT reset the battery monitoring sensor using the scan tool. This reset is reserved for new battery installation. This reset clears the learned battery data, the battery time in service, and affects the aging parameters, which have been learned since the installation of the battery.

The battery monitoring sensor is attached to the negative battery terminal which provides a ground to the sensor. The battery monitoring sensor is integrated with the negative battery terminal clamp and cable assembly and cannot be serviced separately. The battery monitoring sensor measures voltage, current and temperature of the battery and uses these inputs to calculate the battery condition, transmitting this information through the LIN circuit to the BCM . The battery monitoring sensor has a 2-pin connector providing battery voltage and LIN connections. The battery monitoring sensor has to be calibrated at regular intervals. This occurs during a rest period or when the battery closed-circuit current is less than 100mA. The rest period must last for at least 3 hours. The time-frame in which a calibration must take place is 7 days. If the system has been unable to carry out a calibration within this time then it is impossible to confirm the exact state of charge of the battery. Any devices left attached to the power socket that draw in excess of 100mA (or less depending on other battery loads) will prevent a battery monitoring sensor calibration.

The battery monitoring sensor is an input to the Electrical Energy Management software. If the sensor malfunctions due to wiring issues or failure, a DTC will be set. In most cases the Electrical Energy Management functions will be turned off until the sensor operation is restored

If the battery monitoring sensor is removed from the battery negative post, all internal parameters except battery time in service reset to a standard setting. These parameters will be relearned during normal calibration intervals. If the battery has been charged or jump started by connecting directly to the battery post or to the battery monitoring sensor, force an internal reset by removing the battery monitoring sensor from the battery negative post then reconnecting.

That's an interesting pdf, even when it's not refering to Focus MK4 I gues (pdf from 2013).

One thing I noticed today: I had to replace my battery because it got bad after 3 years of insufficient loading (leading to no S/S, parking heater doesn't work) and the service guys couldn't fix it so far.
But the last time in service (November 22) they have updated the BMS or other modules because the BMS reset triggered by the "manual" method now didn't work any more. I mean setting light on, ignition on, 5 x high beam and 3 x break -> waiting for confirmation from flashing battery light. This worked before. Did someone notice that as well? And does someone know if there is a new manual method? My FORscan exteded license has just become invalid since a few days and that would help me now.

I think the BMS reset is a service function that does not require an extended license.

There is a service procedure in FORScan for that car and Don is correct, you don't need an extended Licence to use it.

KOEO "Key On Engine Off"
The correct method to "test" the BMS and charging system is:
1) Completely scan the vehicle (KOEO) and save all network faults with a power supply attached.
2) Delete all faults with KOEO.
3) Start the engine, a new scan can be performed and save all network faults.
4) Measure the alternator output with a DC AMP clamp attached to battery negative.
5) Add loads such as heater motor, rear glass defogger, extra lighting and the DC AMP clamp will read the amperage increase, relative to the loads applied.
6) With the key removed, doors closed, scan tool removed and after the network is in sleep mode, measure the parasitic draw: Max. 0.50mA to Min. 0.20mA. Repair the parasite if evident.
7) Consider all new recorded faults as true and solve those recorded faults to ensure reliability.
8) The BEST and most reliable BMS reset is with a scan tool.

Thanks guys for your input.
I could do the reset of the BMS. BATTERY_AGE is now "0". During my test drive with PC connected I could see the BAT_ST_CHRG (Vehicle Battery - State of Charge) go up from 80 to 88% in the end. S/S was working all the time.
Let's see if the status stays like that...

I noticed that when entering the SBL programming state (Updating another module) generally in the programming state, the BMS started to miscalculate the SOC. BCM RESET didn't help so I decided to do a BMS reset and it didn't help either. So I disconnected the battery from the car, then reset the BMS and only then it started counting fine again. It concludes that any loss of energy, even momentary to the BCM (battery disconnection .... energy discharge) will result in incorrect SOC counting ... BMS reset erases the aging of the battery, and disconnecting the clamps (BMS sensor) from the battery erases the charging and discharge memory battery

I'm going to tag along with this post, we don't have the Mk4 Focus in North America, but I've been trying to figure out why my Start/Stop functions stopped working after a week with a new AGM class battery. FORScan claims the DTC was triggered for wrong battery type. Some things shared on page 1 have given me something to start with. Looks like whatever happened in my vehicle may also be happening here. Just the trigger seems to be different.