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auxiliary stop start battery replacement


Patch58
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hi all/ eco has stopped working on my x250 xf tried charging the battery but still doesn't work so guessing  will have to change the battery, is it just a straight in and out swap or will i have any ecu issues etc,thanks

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Hi

Have you also checked the auxilliary battery? If you are still on your original main battery both could well need replacing but still worth checking both before you do. What voltages do the batteries read? Has the stop/start just stopped working or has it been non-functional for a while? What sort of use are you doing?

With the XF it is worth remembering that every 6 months or so it runs a self-test on the battery by deliberatley discharging the battery down to 75% charge (12.2v). This can run over several driving sessions. Not really sure I like it as always feel it will get to 75% just when I park at the airport for that holiday of a lifetime so I come back to a dead car. 😞 This can be the cause of the Stop/start not working. Stop start only works when the car is sure that there is enough charge in the main battery to restart the engine and enough in the auxilliary to safetly power all of the voltage sensitive components whilst the main one is busy trying to turn the engine over. Both need to be charged for Stop/Start to work.

Secondary battery should just be a straight swap as it is only connected to the sensitive circuits it supplies during a stop/start event but does no harm to wire up a battery tender to keep a supply whilst changing the battery. The main battery should also just be a straight swap only needing resetting of parking brake and windows on re-connection.....BUT there are some horror stories of problems if you don't use a battery tender.

If you do fit new ones make sure they are AGM, as ordinary ones, although a lot cheaper are very likely to fail within months as the charging system treats them as AGM and they do not like it 🙂

John

 

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Hi

Just a thought but make sure you do not attach the earth directly to the battery terminal when charging as the BMS module is in the battery earth lead. If you attach directly to the battery terminal rather than a remote earth point there is no current flow through the BMS so it does not have an accurate idea of how charged the battery is.

Let us know how you get on.

John

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3 hours ago, Big John said:

Hi

Just a thought but make sure you do not attach the earth directly to the battery terminal when charging as the BMS module is in the battery earth lead. If you attach directly to the battery terminal rather than a remote earth point there is no current flow through the BMS so it does not have an accurate idea of how charged the battery is.

Let us know how you get on.

John

Hi John,charged them both took it for a 5 mile run didn't work but I think it will need a good run what do you think and yeah I always put negative lead on the spare wheel clamping bolt

Edited by Patch58
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Hi

I would be looking for at least an hours run with minimal electrical load such as a/c, lights etc as an absolute minimum. If you do not already have one I would also invest in a voltage meter (less than £10 on eBay) as it is quite possible your car is in the middle of a self test so is actively discharging rather than charging the battery.

I would be looking at recording both battery voltages at rest (connect the voltmeter and lock the car then read 30 mins later after car has gone to sleep).  The secondary battery should be at rest anyway so you should be able to just connect that one and read instantly.

Let us know how you get on.

John

 

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Hi

Just re-read and missed you had charged both batteries. In that case forget the run as they should be charged  (Is your charger suitable for AGM as they do have a different charging profile to straight Lead/Acid?).

Next stage is check the actual voltages at rest.

John

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I put two new batteries on and reset the BMS and stop/start did not work. A couple of months later pulled up at a set of lights and the engine stopped. Panic but it was just the car deciding when to start going in to stop/start mode. Done it ever since. If a/c is active then does not seem to go in to stop/start mode which islogical.

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1 hour ago, Big John said:

Hi

Just re-read and missed you had charged both batteries. In that case forget the run as they should be charged  (Is your charger suitable for AGM as they do have a different charging profile to straight Lead/Acid?).

Next stage is check the actual voltages at rest.

John

Hi John use a ctek stop start charger says it will do agm,will check the voltage and get back

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Hi

That charger should be fine and should have picked up if the batteries were not able to hold charge (it is the one I have). Pretty well out of ideas after that so my next action would be to see if there are any DTCs. According to the workshop manual the car may have detected a fault which prevents the sytem working. However  it seems in the absence of warning lights it is probably only a fault that effects S/S so may be one you can live with 🙂

John

Fault Diagnosis

The GWM performs passive and active diagnostics on the dual battery system to determine the status of the system components.

Passive diagnostics can detect faults in the DBJB and can check for stuck open or closed contactors and failure of DBM contactor command signals.

Active diagnostics is a routine to test the capability of the contactors to respond to open or close command signals sent from the GWM to the DBM. This routine also checks the FET's (Field Effect Transistors) activate as required. (Refer to Dual Battery Junction Box below for description of FET operation)

The GWM will also check the dual battery system components for faults in a controlled environment when the generator is providing a charging output. This will ensure that the detection of a fault will not result in sensitive electrical loads being subjected to low voltage which may occur during an ECO stop/start with a fault present.

The GWM will illuminate the charge warning indicator in the instrument cluster if fault is detected in the dual battery system which will result in a degraded power supply.

If a fault is detected the GWM transmits a CAN message to inhibit ECO stop/start operation. In some cases it will record a DTC, display a warning message in instrument cluster and also illuminate charge warning indicator.

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30 minutes ago, Patch58 said:

hi john,main battery 12.53v,auxiliary battery 12.84v

Hi

Auxilliary battery is fine and the main is probably at 80% plus as it takes several hours to get a true resting voltage and the car can take a good 30mins to fully go to sleep.

Good luck

John

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1 hour ago, Big John said:

Hi

Auxilliary battery is fine and the main is probably at 80% plus as it takes several hours to get a true resting voltage and the car can take a good 30mins to fully go to sleep.

Good luck

John

hi john,been left over night and took the reading this morning

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Hi Glyn

If you took the main battery voltage with the car unlocked your measured voltage will almost certainly be at least 0.2-0.3v below true resting voltage as the car starts drawing about 4A as soon as it wakes with an unlock. I use the Ctek Battery Sense bluetooth monitor which at £50 odd is a bit OCD but at least I can then be sure of the battery state 🙂

Short (pardon the pun) of a battery terminal problem such as some corrosion it does sound like a fault in the Dual Battery Junction Box but one that can be lived with as the majority of owners seem to prefer S/S to not work anyway.

I presume you have already checked for the "swimming pool" in the spare wheel well?

John

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