JayArras

Thanks for the link and welcome to the fray, radaddict! Don't worry about the cross-link. The mods don't like it but everybody does it anyway . Besides, most of us belong to the other forums too!

E60I

We all agreed that a good IBS's main job is to put the car to sleep. But, can a defective IBS cause other electronic parts "to turn on" and drain the battery?

Anyhow, I would replace the IBS if the alternator and battery checked out okay.

Good luck!

BimmerFan52

Actually the IBS has no control over putting the car to sleep.

The IBS's three main functions are to measure the voltage, battery current (charge and discharge) and temperature of the battery negative terminal. It communicates via the BSD line with the DME (the cars main electronic module that runs the power management software), trading information back and forth.

The IBS's measurement of voltage, current and temperature are used by the microprocessor in the IBS as well as algorithms in the DME to estimate the battery's SOC or state of charge and SOH or state of health. The DME will then react by signalling the alternator to increase output voltage, increase the engine idle speed if stationary or modify the peak electrical load via system deactivation (turning off systems such as lights, window heaters and other modules).

The IBS measures both during engine operation and after shutdown. After shutdown the IBS will wake up every 40 seconds for 50ms to make quick measurements and then power back down, conserving battery power. The main purpose of IBS measurements after shutdown are to calculate the batteries ability to restart the car. If the IBS senses significant battery discharge (a worsening of the SOC) then it can wake up the DME to allow the DME to attempt to shed load by deactivating systems. This wake-up is designed to be a one-time event.

Early IBS units (2005 and earlier) were susceptible to moisture damage, and both early and later IBS units can be damaged through rough handling (computer chips inside) or the application of jumper or charging cables connected directly to the battery negative terminal (all jump and charging functions should be performed under the hood using the positive jump terminal and the negative ground terminal on the drivers side strut tower) - never connect directly to the battery.

IBS failure can result in repeated awaking of the DME and run down the battery, or interrupt the DME starting diagnostics and prevent the car from starting altogether.
Disconnecting the IBS BSD line will cause the DME to ignore the IBS. If the IBS was preventing starting the car, disconnecting it will now allow the car to start. And if the IBS was continuously awakening the DME and running down the battery that action will cease.

Leaving the BSD disconnected interrupts the SOC and SOH information gathered from the battery. The DME will then set the alternator charge voltage to a default 14.3V. This may shorten battery life a little or cause excessive battery gassing during elevated temperatures (reason terminal temperature is measured and alternator charge voltage adjusted by the DME) and also removes the ability to wake the DME in the event another system is not shutting down and draining the battery.

If you google IBS replacement on this or other forums you should find a good DIY. The key is to be gentle with the IBS and avoid over-tightening the bolt on the battery terminal clamp itself, as if the aluminum part is stripped you will have to buy a third one.

JayArras

You're making my head reel here! In an earlier post, you stated above that if any of the symptoms you mentioned are NOT present, it's most likely the battery that is preventing the car from starting.

In your most recent post, you're saying it's most likely the IBS that's preventing the car from starting.

Based on my most recent experiences, I'm leaning toward that theory, and will test it should I start to experience symptoms again. In the meantime, I've gotten almost 7 good years out if that battery, so if it goes, I won't be hesitant about replacing it AND the IBS.

BimmerFan52

No, I did not say in my last post that I think it is your IBS.

Your head is reeling because according to your posts your symptoms keep changing. I am not saying that is your fault - the symptoms are what they are. But one can only troubleshoot by odds. If symptom X and Y exist, from experience the greatest odds are the cause is Z. Troubleshooting, especially via email is full of shortcomings.

In your first post you said the engine was very sluggish and slow to start. 999 times out of 1000 that will be a battery low on voltage. Secondarily, the fact that it is low on charge does not necessarily mean that the battery is at the end of its life, but again without other proof that that it is not being charged or is being unnaturally drained, battery end of life is the greatest probability.

Later you said that at the auto store when you turned the key it would click but not start even if an auxiliary voltage was applied to the system (jump start). Clicking generally means the solenoid is being sent voltage and activating but the starter motor won't energize. 999 times out of 1000 that means the starter motor is going.

Then your discussion turned to your IBS as a possible cause.

I offered that if it is the first type of IBS failure it would prevent the DME from sending a voltage to the solenoid. No click, no nothing. Not what was described in your first post of sluggish engine turn-over, or your second experience where when being jumped it would click but not start. If it is the second type of IBS failure that continually wakes the DME and drains the battery that might explain the sluggish starting of the first post, but neither mode of failure would allow the solenoid to engage but prevent the starter motor from turning over while being jumped in your second post.

I ended my last post by saying that it is worth a try to disconnect the IBS and see if your battery stops discharging. It is quick, easy to do and costs you nothing. But if you think I was suggesting your main problem (or your only problem) is the IBS you misunderstood.

Could you have more than one component intermittently failing? Absolutely. My battery was replaced (4 years old) so that was to be expected. Then my alternator voltage regulator failed four months later (after the dealer checked it while replacing the battery). Coincidence? Maybe, but I think the already intermittent alternator killed the weak battery before the alternators pending failure was apparent. My voltage regulator would be fine one day and jump around like crazy the next. Only by constantly monitoring the voltage was I able to identify the problem. No mechanic can spend the time in your car that you do.

If troubleshooting were easy there wouldn't be so many posts of experiences by owners that go to dealers or repair shops who begin replacing components (and charging for them) until either you run out of money or they stumble upon the root cause. Kudos to your mechanic who declined throwing parts at the problem in the hopes of a solution.

First, IMHO you got your money's worth out of that seven year old battery, and regardless of what anyone says I would immediately buy a replacement battery at Autozone (don't read the cross reference charts at the store as they are incorrect). Search this site for the correct battery number and replace with it with the same type battery (likely a flooded lead acid). Have your mechanic install it if you don't feel you can do it, and if he can register it all the better. If not, optionally you could have a BMW indie register it for you for around $50.

Then hang in there and see how it reacts. If your brand new battery runs down continue your search.

I would also recommend you learn how to use a multimeter ($5-$10 at Harbor Freight tool or Walmart) or buy a cigarette lighter voltmeter ($5-$15 at an auto store or on the web) and begin monitoring your battery voltage before starting, and your alternator charging voltage after starting and during driving.

JayArras

Thanks for your detailed response and advice, BimmerFan. I guess I did misunderstand. There's likely a lot going on here, but it helps if you look at the issue methodically like you suggested. I will take your advice and look into purchasing a meter to monitor things. Thanks again!