Battery voltage

[Marcozi]

I replaced the factory battery in my car (2018 BMW M240i) last January with an Odyssey battery. The car and the battery were 7 years 5 months old when I replaced it. I bought the battery from FCP Euro. I made sure the car's electronics knew the battery's capacity and that it was a new battery. I've got some codes in the car which seem to be electrically related. The codes, using the bimmerlink app, are:
- 48276E - Autosar - standard core - volatile memory error- integrity failed
- 4827B3 - internal control unit - undervoltage at terminal 30
- 4827A0 - SBS function-roll rate: error amplitude due to suspected error
- 48274A - SBS function-pitch rate: error amplitude due to suspected error
- CDA506 - FA-/LP-CAN, message 19 from EGS
Note, EGS in BMWspeak is the automatic transmission computer. The car has a manual transmission!
I tried clearing these codes but bimmerlink would not clear them!!
Note: The "4827" codes are for the integrated chassis management module

I checked the car's voltages at the jumper connections under the hood using a Klein Tools DVM. With the car awake, but not started I got a reading of about 12.6VDC. Idling voltage was about 13.7VDC. Now, I switched the DVM to ac with the engine idling, and I saw 76vac for about 0.25 seconds, but approximately every 2 seconds. The car starts on the first try without hesitation. It's not driven on trips less than 20 miles.

Ideas?

 

[barryh]

If you read 12.6 volts dc with the car awake and pulling amps, which it will be then you don't have low battery voltage. The AC reading is irrelevant.

 

[Marcozi]

If you read 12.6 volts dc with the car awake and pulling amps, which it will be then you don't have low battery voltage. The AC reading is irrelevant.

Why isn't the ac relevant. I thought it meant that the alternator has a problem.

 

[The_Jeff]

I suspect the regularity of the AC voltage is by design, and you're picking it up through an instrumentation anomaly. Either BMW does this on purpose to test or desulfate the battery, and/or they've engineered in a reason that only they know about. Can you pick up these AC currents on an AM radio?

You may also have a very sensitive meter and are getting just "stray power" of no consequence at all.

This is like people that test their batteries way too often then freak out when a reading drops even though things work fine. We didn't have fancy digital testers 20 years ago and lived to tell about it.

 

[barryh]

Why isn't the ac relevant. I thought it meant that the alternator has a problem.

Excessive ripple on the alternator output can be an indication of problems but that would be 0.5 volts not 76 volts.

I think it was just a case of getting a crazy reading because the DVM is set wrong and that's why I said it wasn't relevant, especially given the DC voltage measurement was good.