Driving it with the scanner running, it’s showing 14.0-14.2 V while driving around 50 mph. When I stopped at a stop sign, foot on the brake, it dropped to 13.2V.

The thing that makes my gut keep coming back to the alternator is the battery died a couple times a few months ago. I took it in to the auto parts place to get it tested. They took it in the back, told me it was being tested and would take a couple of minutes. I took it there because the battery was a Bosch with a date showing it was 10 months old. 10 month old batteries don’t normally go dead. They can but it’s unusual. After 40 minutes they said it wouldn’t complete the test and they honoredthe Bosch warranty and handed me a new battery for free.

That seemed to resolve the dead battery problem.

Maybe I’m wrong and I’m trying to project the problem onto the alternator but the fact that a few miles earlier, it was showing Engine Failsafe with the DSC Disable message and Brake light come on makes me think it’s electronic not mechanical.

I guess I’ll pick up the 510 scanner. Can I read the ECU with that or is the 520 needed for that?

The dreaded Trans Failsafe Mode (again)
 

510 520 basically identical.

If you have mystery battery death check the starter current.

If you have a peak reading DMM you can measure voltage from cig lighter to the B+ jump point during a start. It shut be about 0.75V if the engine is warm but not started in the last few minutes. A restart should be about 0,65V.

Multiply by 280 to get an estimate of amps.

While stopped the voltage typically recovers. It's exactly while coming to a stop when the voltage Usually dips. Also that's when the trifecta will come on. So basically you need to be monitoring for a voltage dip right when the trifecta kicks in. That will indicate with certainty charging circuity problem.

Random ghost abs defeat that can't be traced, usually is the abs module. Often temperature related. If your abs works most starts then defeats regularly wheel sensor then abs module likely culprits

A failing ABS module has been known to cause the X5M5 to go in trans fail safe Mode. After establishing that it’s not voltage related I would check out the ABS module.

Just ordered the NT 520, so we'll know more mid part of next week.

The dreaded Trans Failsafe Mode (again)
 

The 520 will do an auto scan so start there. Use "save" for each error so you can "replay" those later before deleting the codes. Erase codes from each module and re-scan to see if they stay clear.

Then you will test drive and see if errors return. You will see a lot of errors the first time most that set long ago when there was a low voltage situation or something so that's why you have to clear first for a clean slate.

Climb under the car and take off your transmission connector and make sure it's clean. I spent a week chasing transmission Gremlins before I find out my connector is full of rusty water! That was my only problem.

If your battery checks out you may want to examine / clean your MAF

Thanks, already did that. Took the Idle Air Control Valve off and cleaned that, as well as cleaning the MAF sensor with MAF cleaner. I've driven it about 10 times since I cleared the codes for lean bank, IAV stuck open, and so far, no engine codes have returned. I'm trying not to drive it, other than for testing, until I can get that scanner and get the trans failsafe cleared (hopefully I can do that with the NT-520).

The 510 will clear and read trans codes. It will also show many Realtime data points like shift solinoid value etc. Did you check the connector yet?


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I have not checked that yet but it's first on my list when I start working on it this week.

My scanner came today. Bought the 520 off eBay on Friday, came today, Monday, from the other coast. I don’t buy much off eBay, but $159, free shipping. The guy has sold many, so I took a chance and it looks like it worked out.

Plugged it in, ran the auto scan, saved that, then reset everything. Transmission failsafe error is gone, transmission working perfectly again. After a few miles, the check engine light returned with the same error it’s had for months, P1093. I’ll chance that down now.

I’ll also work on a graph of the alternator. If anyone can kindly direct me to the right path to get there, I would appreciate it. Looks like learning the diagnostic tree structure is going to take me some time. Not knowing what’s available or what many of the acronyms stand for, it’s a little slow navigating.

But super happy so far. Money well spent.