it happened to me twice, first time it happened, i changed my oxygen sensor, and forgot to put the wire back into the slot, so it was dangling on the hot manifold, which threw the failsafe error.

the second one was the abs module. first i changed my abs sensors, brake pads, and finally abs module which cleared the error both the failsafe and abs error.

Made some "progress" on this one so I thought I'd post a follow up.

About a month ago the Trans Failsafe message returned (after being absent for a couple months), this time paired with "selflevel susp. inact". An error I hadn't seen that since replacing both front air struts and a ride height sensor back in May. I had an indy triage and apparently the Air Suspension Control Unit needs to be replaced. I've read a lot about this suspension system but this was not a component on my radar for likely failure. I can source a new control unit for a couple hundred less than the shop but does anyone know if they need to coded or calibrated after installing?

In addition, they're saying that they're seeing intermittent spikes in voltage coming off the alternator and that it too needs to be replaced. And that they won't warranty the new Control Unit unless I replace both, implying the control unit may have been killed by the alternator.

Does this pass the sniff test to you guys? I'm thinking about starting with the control unit (maybe even used off eBay) and go from there.

Doesn't sound unreasonable to me.

I'd ask for more specifics about exactly how they're seeing these spikes and what they look like.

To me, yes, this whole thread points toward voltage fluctuation issues more than AT or brake or suspension issues.

It could be connections rather than an actual component.

And if you decide to replace the alternator, I'd consider just replacing the voltage regulator. Speaking from having rebuilt my Valeo alternator on my 2001 3.0i, it's pretty solid outside of the VR - meaning not much to go wrong. I replaced bearings, slip rings, and brushes (and had swapped in a new VR a couple of years ago).

So actually, based on what you're "thinking," I would do the opposite - starting with the alternator, and then moving on to the control unit or whatever problems remain.

Tough going with these intermittent electrical problems. It is so easy to replace too many things that don't need it. And hard to avoid that.

Good luck, and thanks for keeping us posted so we can learn from however things turn out.

BMWs are extremely sensitive to voltage fluctuations. Absolute must to get alternator operating 100% before you waste time and $ on things that operate on Electric power.

I had trifecta and trans failsafe from only voltage fluctuations. $20 repair kit on my alternator fixed all the gremlins

Thanks oldskewel and andrewwynn.

Below is what the indy had to say about the intermittent spikes in voltage. I might have more info when I pick it up later today.

"Alternator faults present. Monitoring of charging system shows
intermittent voltage spikes of over 15 volts."

Based on your recommendations I will start with the VR and either rebuild or replace the alternator before diving back into the air suspension related errors.

Alternator replaced and I believe at this point we can mark this one solved.

All errors/lights such as trans. failsafe prog, selflevel susp. inact, brake, abs, etc vanished post repair and haven't been seen since.

Glad I came here, listened to oldskewel's advice and didn't start with the $750 control module that it turns out I didn't actually need.

Many systems require solid voltage it's not surprising at all to see all the problems vaporize. Great news


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