Testing for bad Battery Safety Terminal?
 

Hey all - just picked up a "parts" 4.6is today. Turns out it may be a better car then I was expecting so I may trying and fix it up.

One thing - airbag light is on and previous owner says the problem is the BST.

Car was in a slight rear end collision - no airbags were deployed. He says the problem is the BST on the battery cable.

The car runs and drives fine, actually. Reading about the BST it typically says BST goes bad and the car won't start.

So just wanted to see what folks here had to say. Is it possible the BST is bad but the car still starts? Is there a check for this issue?

Thanks!

Testing for bad Battery Safety Terminal?
 

BST blown you can't start the car without jump start and won't charge the battery.

BST is a literal circuit breaker between battery and alternator/starter.

When you have BST symptoms ish you need to check the B+ terminal at the firewall. If it's loose you'll get symptoms like a loose battery terminal.

First off what codes does it show and second what scanner are you using?

There have been times where folks had a BST giving similar symptoms before but it's such a simple, cheap fix that I would have thought the original owner would have taken care of the "one" [emoji1787] thing that made his X5 unreliable.

So let's just see what current and pending codes show up before any money gets thrown for parts.

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So to be clear - this wasn't the only issue. The kid selling it just didn't want to fix it up, and I think he was pretty honest about everything wrong. It was also super cheap. However, the engine runs strong (new chains too) and shifts great but it needs a ton of little things. Fine with me, fun winter project. Worst thing I have a parts car for my much nicer 4.6

I'm using a Launch and will have to plug in for codes again.

I've read BST can allow the car to start but cause airbag errors hence my Q. Will post back with more.

I have heard a couple of the guys have BST issues like you described (not 100% same) but I have also found that with a good battery many e53's with similar issues had connection problems with the B+ or the ignition switch.

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Good to know. There is lots of cleaning and checking for me to do tonight, although I may be in luck. Looks like the car had the recall done which means I have the OEM splice already done. That means I just need to find a good used battery cable and I can just cut the end off and use that with the replacement connection (if, in fact, the BST is the problem). The plastic ends look pretty nasty so I may just swap it for cosmetic reasons.

Will keep you all posted with codes and as I learn more.

If the car starts BST not the problem. Other end is where to look for problem.


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Is it possible the BST has been "spliced" or by-passed and the SRS system cannot read the BST status or has a code for a BST "fired"?

Remember, the BST is part of the airbag (SRS) system and is possibly monitored like the other SRS components.

The BST can be coded out according to a discussion on bimmerworks but I have no idea if it will show up as fired or maybe unlisted in that case.

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That's a good point.