[thefrog1394]

Had a no-start condition that was resolved by unplugging the IBS power wire.

Car has been in an accident and there was damage around the battery area. Also, looks like it might have gotten wet in a recent storm. So a bad IBS seems very likely.

Car has an aftermarket AGM battery that was registered when new and has been working without issue for a few years.

I don't really want to buy a new IBS if I don't have to b/c this is an old car and it's very likely that due to the damage in that corner, new IBS will just get physically damaged again in the future.

So, what happens when the IBS is unplugged? Do I run the risk of undercharging or overcharging the battery? Has anyone done this long term?

I don't mind if battery life is slightly worse, but if this is going to lead to deep discharges or overcharges during normal operation unlike a traditional alternator setup, then I'd be more concerned.

[thefrog1394]

From https://www.e92n55.com/wp-content/up...us-systems.pdf

A fault code is stored in the DME when the IBS is defective. The DME adopts a substi- tute value and assumes IBS emergency mode. IBS emergency mode boosts the idle speed in order to sufficiently charge the battery.

That paper also indicates that one of the roles of the IBS is to ensure the battery has enough power to start the car one more time. Presumably without the IBS operating, either the car will be more likely to drain the battery dead when sitting, or some power-hungry functions (i.e. HVAC rest function) might be unavailable? (All just guesses here). The paper indicates that low SOC when parked will cause the car to shut off auxiliary loads. I'm just not sure what auxiliary loads this car has... it's not a Tesla with an always on internet connection or something.

[thefrog1394]

With the IBS unplugged, the car seems to hold the alternator around 14.2v (at least at idle). Seems reasonable. Maybe a little high for the AGM battery on long trips. I think I'm just going to leave it unplugged and see if I notice any issues.

[JoshHawks]

I had my IBS unplugged for about a year before even realising it was unplugged with no issues what so ever. Didn't notice a change when I plugged it back in either so you should be fine, just more likely for the battery to drain if it's left standing for a long period of time