You’re driving a BMW which has a reasonably old battery, like 2 years of age. All seemed to be working well until one morning when you found your car completely dead. No lights, iDrive, starter function, just dead battery on your beloved BMW. The night before you went through one of those touchless car washes with the undercarriage spray. And now you wonder if water got somewhere it shouldn’t have. You’re wondering where to start looking for answers. Here’s a guide for troubleshooting dead batteries on a BMW.
Don’t rush out to buy a new battery just yet. And if you have aftermarket devices installed on your car (like a DVD player, for example), do not rush to the dealer either: they will most likely blame the dead battery on your aftermarket gear and make you strip your car off of those before coming back for a re-check.
Unless your car is under warranty still, raising the dead battery issue with the dealer, from what most BMW owners report on plenty on forums, will likely lead to your being sold a new battery. If that doesn’t work out well, they might sell you a new alternator and possibly other electronic modules.
Bottom line: it may be quicker and way less expensive to troubleshoot the dead battery yourself first. Just try the quick and easy steps below before purchasing expensive replacements.
Recharge your car’s battery
Until you recharge the battery, there is no test you can perform.
How do I charge my BMW battery?
BMW recommends that the battery is charged via the jump start terminals under the hood. First, disconnect the battery from the car. Connect your charger now, red clamp first and proceed to slow charging the battery. A dead battery can take up to 24 hours to fully charge. Do not let the key in the ignition while the battery is charging.
What is draining my BMW battery?
Below are the possible reasons for a high battery discharge in a BMW and how you can test them:
- Plugged in external devices
- Plugged in OBD-II scanner
- BMW Intelligent Battery Sensor
- The infamous ”hedgehog” (from the climate control panel)
- One of the electronics on your car drains too much power or does not go into sleep mode
- Faulty alternator
- Old battery
Plugged in external devices
Cars use an alternator, a device that recharges the battery while the car is on the move, using as a power source precisely the energy generated from the car engine. So basically the car has a way of recharging itself.
But this only works when the engine is running. If the car is parked, there is no source of energy in use, just a limited capacity battery. And you only have power being drawn from the battery (by the plugged-in device) and nothing recharging the battery. This is why forgetting your headlights on led to the dead car surprise on your return to the car.
So if you had a dead battery and you just recharged it, make sure there are no external power consumers plugged in. Any chargers or adapters in the cigarette outlet?
Plugged in OBD-II scanner
While there may be instances when you need to keep an OBD-II scanner plugged in to investigate an issue you have with your car, depending on your OBD-II scanner specifications, it might not be a good idea. Some OBD-II scanners draw more power from your car than others. This will not be a big problem while driving, but it can drain the battery when the car is idle. If you need to leave an OBD-II scanner plugged in, you probably do not need it overnight.
BMW Intelligent Battery Sensor (IBS)
What is the BMW IBS?
The 5 Series BMW (E60, E61) and the 3 Series (E90/E91/E92/E93) have a device called Intelligent Battery Sensor (IBS) attached to the battery negative terminal (the ‘-‘ or the black terminal, whatever terminology you prefer).
What does the battery sensor do?
The IBS contains a microprocessor that monitors various battery conditions: voltage, current, temperature, starting current and something called closed-circuit current. When the car is currently, the IBS is permanently active and monitoring. When the car is parked, the IBS wakes up every few seconds, performs the tests and goes back into sleep more to preserve battery power.
The infamous BMW IBS
The early models of E60 and E61 had an IBS prone to moisture infiltration and corrosion. These faced the faulty IBS issue by the hoards. Later 5 Series cars and the 3 Series face faulty IBS problems too. If the IBS is faulty, it can prevent your car from going into sleep mode and causes the battery to go flat.
How to test if the IBS is faulty
To test the faulty IBS hypothesis, you simply have to disconnect it from the negative terminal of your battery. To disconnect the IBS, remove the little red wire that goes into this tiny module. There are plenty of online videos for removing an IBS from a BMW battery.
If the battery draining disappears once the IBS is disconnected, you have your culprit. You can then go ahead and purchase a new IBS online.
The infamous ”hedgehog”
BMW E39, E46 and E53 Final Stage Resistor (FSR), also known as the infamous ”Hedgehog”, has been causing battery draining in huge numbers. The FSR gets its nickname from its looks: it looks spikey, like an angry hedgehog. you can also find it under the name of blower motor resistor or heater fan resistor.
The FSR component is connected to your car’s HVAC system (Heating, ventilation, and air conditioning). But this does not mean you are supposed to experience issues with aircon, ventilation or anything of the sort. Although some people report the car fan remains on even after they shut down the car.
To test if your FSR is faulty, you don’t have to buy a replacement hedgehog. Just remove the fuse corresponding to this component. To see which fuse corresponds to the FSR and where it is located, check you BMW’s user manual. Chances are high you don’t keep around the house a printed copy of your e39’s user manual, so just look it up online. Or just follow one of those How to replace a FSR online videos.
Module drains too much power or does not go into sleep mode
The telematics control unit (TCU)
Check if you have a The telematics control unit (TCU) on your car. This is known to cause the drained battery when it is faulty. Check out what the BMW TCU looks like. If you have a TCU on your car, it is located in the trunk, behind the trimming. Online videos will help you located the TCU. The following car models may have TCU modules installed: MW 1 Series (E81, E82, E87, E88), BMW 3 Series (E46, E90, E91, E92, E93), BMW 5 Series (E60, E61), BMW 6 Series (E63, E64), BMW X5 (E53, E70), BMW X6 E71.
To test the faulty TCU hypothesis, remove the fiber optics connector from the unit and replace it with a MOST loop female bypass connector. If you do not have a MOST bypass connector, you can just leave it disconnected. Just keep in mind that this might lead to your sound amplifier being disconnected too. No harm will be done, it’s just that you will not hear music until you reconnect the TCU or fit a MOST loop connector. But it will help you test if your TCU is causing the dead battery quickly and without additional costs.
If your TCU was causing the dead battery, you can look for a BMW TCU repair service.
The iDrive main computer (navigation)
Two iDrive navigation modules are notorious for causing dead batteries overnight: the CCC iDrive and the M-ASK iDrive navigation. To test if any of the two is causing you trouble, either:
locate the units and disconnect them. To disconnect the M-ASK or the CCC iDrive, you have to pull out the connectors that plug in the rear panel of the units. To access the modules’ rear panel, you have to remove them from the dashboard and this takes a little bit of work (there are plenty of video guide on YouTube)
an easier test is to look up the fuse diagram for your car, identify the fuse number and location corresponding to the CCC or M-ASK and temporarily remove the fuse.
Once you confirm you have a faulty CCC, you can use a CCC repair service. We also offer a M-ASK repair service, in case your faulty iDrive is a MASK model. Unfortunately the dealer will not repair these units, although both are perfectly repairable in all cases. The dealer will only sell replacement units at a considerably higher price compared to a repair service with 1-year warranty.
If you do not have the above three electronic modules on your car, there is still hope for you to see if one faulty module is draining your car battery. Check out this extremely informative, easy to follow and entertaining video for finding a short in a car.
A defective alternator will not charge the battery properly. Some auto repair shops offer charging system tests for free. Try to Google an offer like this and if none shows up in your area, it might be worth paying for a test before resorting to purchasing a new OEM battery, if that is your next move.
Your last resort would be to replace your car battery hoping your old battery was simply too old and weak. The ones sold by BMW (OEM batteries) are very expensive. You don’t have to buy an OEM battery. A properly chosen aftermarket battery (something from ACDelco or DieHard, for example) will do perfectly fine. It’s important to go for a replacement battery with specifications matching your OEM battery as close as possible.
You can have your battery replaced at the dealer’s (if you buy the OEM expensive battery), at an independent repair shop, not necessarily one endorsed by BMW (if you buy an aftermarket battery) or you can replace your BMW battery yourself.
Does a BMW battery need to be reprogrammed?
Mind that many online resources and the dealer too advise that you must register and code your new battery on your car after installation. While some DIY enthusiasts report no consequences from using a new BMW battery without any coding, if you replace it at an indie shop, you might want to ask about this option or do a more in-depth online search on this topic for your particular car model.
Wrapping it up
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