E82 120D - Occasional no power when parked

[bluezedd]

Hi guys,

I'm asking on behalf of a friend who has been having a no power problem with his car. It's an E82 120D.

He has twice had a problem where after the car has been parked up for a while, there has been no power and has had to use the physical key to gain entry.

Once in the car, there is no power to the car, even when the key is in the ignition.

This is what I did:

1. Powered the car from the bonnet terminals to gain entry to the boot using a 12v car battery.
2. Checked voltage of the battery in the boot. It was good at 12.4v (note all checks were done after disconnecting the extra battery).
3. After giving the car power at the bonnet terminals, I removed the power, and we started the car with no problems and it cranked fine using the battery in the boot.
4. Alternator is charging the battery fine.
5. Voltage drop during cranking is fine.
6. Checked battery connections in boot and are mounted ok.

I was wondering if you guys had any idea why the car would be totally dead, but then just adding the 12v battery to the jumper point for a second would result in everything powered up and working ok?

Note, we didn't leave the battery connected to the jumper points when starting the car, checking voltage etc.

Thanks for your help guys

[RUSSELLM]

That’s a weird one.

Do you think the car is going totally dead ? When he sets the alarm, does an LED flash ? If so, is that still flashing when he comes to the car during the ‘Dead car fault‘ being present ?

I don’t suppose a previous owner has fitted a battery discharge relay ? Basically protecting the battery when it drops to a defined voltage ?

[bluezedd]

RUSSELLM said:

That’s a weird one.

Do you think the car is going totally dead ? When he sets the alarm, does an LED flash ? If so, is that still flashing when he comes to the car during the ‘Dead car fault‘ being present ?

I don’t suppose a previous owner has fitted a battery discharge relay ? Basically protecting the battery when it drops to a defined voltage ?

Hi Russell, yes it is pretty weird as I was expecting the battery to be dead either due to alternator issue, something left on overnight, or just an old battery.

I'm not certain exactly what happened when the car went totally dead, but know that the central locking didn't open when the physical key was used, and there was an alarm noise (i think from the rear) when he got into the car, while everything else remained dead.

I've read up online about an "intelligent battery sensor", and I'm beginning to suspect this might be the problem in this case. I could be wrong though as I'm not familiar with BMWs.

There wasn't any sign of an additional relay fitted, and there's aftermarket extras that might be causing problems either.

Thank you for your help!

[RUSSELLM]

I’ve not tackled anything on BMW myself, so feel free to disregard everything ...

If it’s stop/start, it may be worth checking it’s had an AGM battery fitted and registered. Failing that, as you mentioned, the IBS may need looking at.

[helix402]

A voltage check isn’t the best way to test the battery. A battery tester will give a more accurate useful reading.

[Elliot2000]

I’m guessing you have an agm type battery fitted - probably original from build- they are amazingly resilient batteries which can take being heavily discharged and survive easily - it’s what they are designed for.

I would be looking at an intermittent battery drain and on an e82 120dof that era - my first suspect would be the fuel heater on the back of the fuel filter. You can just unplug and see how it goes or u could keep checking it a few hours after turning off the car and see if it’s getting warm.

If u happen to have keyless start- three little lines on top edge of door handles (fairly rare on a one series but you do see them) - then door handles Themselves Were another candidate for intermittent battery drain

[Gary C]

So the car is totally dead, but when provided with enough voltage it resets then the car can start off the un-recharged battery ?

Almost if the battery terminal voltage has dropped below a cut off voltage.

I would replace the battery first. Its an easy thing and will remove that as a cause so that if it still happens you can focus on the fault.

But I bet a new battery will sort it.

For years, never had a problem with a lead acid, but these days I have had symptoms similar to what you describe on a Peugeot 407, a Clio and my 911, though they would need some charge to work but would be fine then suddenly, no power.

Edited by Gary C on Sunday 6th September 17:59

[bluezedd]

RUSSELLM said:

I’ve not tackled anything on BMW myself, so feel free to disregard everything ...
If it’s stop/start, it may be worth checking it’s had an AGM battery fitted and registered. Failing that, as you mentioned, the IBS may need looking at.

Thanks Russell. I’m not 100 percent on whether it’s stop-start or not as if it’s there my friend will have disabled it. I suspect we may have figured out what the issue is, but will need to see.
The battery is an 80aH standard lead-acid Yuasa battery from 2019, but the software had it programmed in as a 90aH AGM battery. Perhaps this has led to the issue of the power being cut off. I don’t have enough knowledge of modern cars though to confirm this is the case though.

helix402 said:

A voltage check isn’t the best way to test the battery. A battery tester will give a more accurate useful reading.

Thanks helix. Proper battery testers are great bits of kit and I will hopefully get one soon. I’ve had batteries that have shown 12.6v but then drop to 9v when attempting to crank in the past.

Elliot2000 said:

I’m guessing you have an agm type battery fitted - probably original from build- they are amazingly resilient batteries which can take being heavily discharged and survive easily - it’s what they are designed for.

I would be looking at an intermittent battery drain and on an e82 120dof that era - my first suspect would be the fuel heater on the back of the fuel filter. You can just unplug and see how it goes or u could keep checking it a few hours after turning off the car and see if it’s getting warm.

If u happen to have keyless start- three little lines on top edge of door handles (fairly rare on a one series but you do see them) - then door handles Themselves Were another candidate for intermittent battery drain

Thanks Elliot. Since seeing my friend again, it turns out the battery has been replaced with a lead-acid Yuasa with 80aH dated as 2019. The battery had been programmed in as being last replaced 40k miles ago, and was set to a 90aH AGM battery. The battery has been recoded for the correct values and as a lead-acid, so hopefully this might sort the issue.
If not, we will try unplugging the fuel heater and see if that solves the issue.

Gary C said:

So the car is totally dead, but when provided with enough voltage it resets then the car can start off the un-recharged battery ?

Almost if the battery terminal voltage has dropped below a cut off voltage.

I would replace the battery first. Its an easy thing and will remove that as a cause so that if it still happens you can focus on the fault.

But I bet a new battery will sort it.

For years, never had a problem with a lead acid, but these days I have had symptoms similar to what you describe on a Peugeot 407, a Clio and my 911, though they would need some charge to work but would be fine then suddenly, no power.

Edited by Gary C on Sunday 6th September 17:59

Thanks Gary.
You’ve described the situation exactly how it was. The car was dead, but connecting a 12v battery to the jump points for a second made everything jump back to life. The car was then perfectly fine off of its own battery that was in the boot, and cranked over strongly.
I suspect you might be right with there being a threshold where the car has cut off the power and resulted in this situation.
We found that the specs for the current lead-acid battery was not the same as the one the car had been coded with (80aH lead-acid battery in the car, coded as 90aH AGM). The battery is from 2019, so although I don’t know a lot about the system of coding batteries to cars in modern vehicles and the potential consequences of not doing it correctly, perhaps this may have been the issue.
We ended up using the bimmercode and bimmerlink apps to “replace” the battery for the correct spec one.
To tell the truth, I’d need to double-check that an 80aH battery is suitable for the car, as perhaps it is supposed to have a higher spec AGM in there.
Thanks for the help everyone. Hopefully that’s it sorted for now. If not then we might just add a new better spec battery if it’s supposed to have an AGM one with higher aH and see how we get on.

[helix402]

Hope it’s sorted. Good to have some feedback when others give advice. 👍🏻