Just to add, i do not have any error lights currently on the cluster

 

If it were in my shop, I'd likely be performing a alternator charging "ripple" test on our handheld scope. I'll betcha one phase is spiking and/or you've got a bad diode?

The over voltage ones bother me.

Replacing the voltage regulator isn't that hard of a job and would be worth a try.
It's also a great time to go over all the power and ground spots.

 

OP, be advised that BMW sourced alternators for the E46 from Bosch and Valeo. They are not interchangeable! The only way to tell which alternator is in the car is to read the label on the back of the alternator. Keep your fingers crossed it’s a Bosch. The voltage regulator for a Bosch alternator is a lit cheaper than the regulator for a Valeo alternator. BMW may have installed only 1 brand of alternator for the M3. Doug, can you confirm?

 

Thanks for the responses, i will need to check what alternator is on the car.
Should I be replacing the battery as well? I believe 11.7v when car is off is a bit low?

 

A typical car battery has 6 cells in it. Each cell is 2.1V so in total, you should be getting 12.6V with a healthy battery without the engine running. Voltage is easy to measure. In your case, 11.7V is low.

In addition, don't forget the health of the battery affects how much power that it can provide over a defined time period. This is related to how many amps the battery can provide over some defined time at sufficient voltage. To test this requires you to measure the amperage of the battery which is much more difficult than measuring the voltage. You can take your battery to an auto-parts store and have it load-tested.

When the engine is running, the alternator provides the power to run most everything, including charging the battery. In order to charge a healthy battery (12.6V), you need a higher voltage in order for the current to flow from the voltage regulator to the car battery. As such, most alternators will have a voltage regulator at or about ~14V. The alternator produces alternating current and this requires a bridge rectifier to turn the alternating current to direct current, which is what the car uses. If this rectifier is not working properly, you will see some ripples from the alternative current on an oscilloscope. You need an oscilloscope because these ripples are AC in nature, thus you need to look at time over a time scale. Most of us do not own an oscilloscope. A healthy alternator with a healthy voltage regulator will provide a very steady DC voltage of ~14V with very little (tiny) amount of ripple.

From what you have described so far, I suspect you will need a replacement battery and a replacement voltage regulator.

 

Seems like alternator was replaced in 2016 at 109,591 miles Then again in 2017 at 128,599. I wish they had part numbers on the invoice, but it does indicate (Bosch) on the line item. Car currently at 149K.

 

Alternator only creates AC voltage inside itself. It pumps out DC so testing on Vac will give you odd readings. Should be set to Vdc. As it's had 2 alternators fairly close to each other then that would indicate something else is causing the regulator to fail.
One of the faults was the main relay and as it's a high current relay then burnt contacts within the relay can cause weird issues as it's not so much the voltage but the current that gets to pass through the contacts.
So get the battery load tested after a good charge off the vehicle, replace the regulator and replace the main power relay.

Electronics don't like it when they don't get steady voltage and current supply so can easily lead to weird fault codes arising.

 

Alternator only creates AC voltage inside itself. It pumps out DC so testing on Vac will give you odd readings.

Normally a working alternator should output mostly DC current and very small AC voltage (ripple from the rectification), but we are thinking this one is having an issue and so it's good idea to measure the AC part of the output, and the measured 29.8Vac proves that the alternator is bad. This is why the battery doesn't have full charge and only 11v.

 

It's better to take the car for a quick drive with cluster test set to 9.0 (battery voltage) than to rely only on external voltimeter measurements, which may not necessarily reproduce the issue.

Recently a friend ask me to help him inspect his Z4m, which had the the cluster, and the navigation screen occasionaly flashing and resetting. He is an electronics engineer and was already suspecting the alternator, but failed to find anything abnormal with his tools.

I set the cluster to 9.0 and we took off. Everything was fine during the first several minuters, and the voltage stayed between 13-14 something V. Then it started spiking up to 19-21 when the engine was revved above 4-5K RPM accompanied by radio, cluster lights etc. cutting off and restarting at the same time.

So, a new voltage regulator has been ordered.

 

I think what we're trying to determine here is whether there's a problem with the battery, the voltage regulator or the alternator itself. There could be a combination of the 3.

 

That's better.
Under normal conditions??

 

Under normal conditions??

about what? Oh, you meant what is the Vac component of the normal working alternator? I would say around 0.5v or less measured on the batt.

 

We'll you made a statement "DC Voltage, straight off the battery."
And I'm struggling to understand where the break point is along the DC Bus is where it's unstable and stable.... Given that the cable runs from the alternator to the battery.

 

We'll you made a statement "DC Voltage, straight off the battery."
And I'm struggling to understand where the break point is along the DC Bus is where it's unstable and stable.... Given that the cable runs from the alternator to the battery.

OK, the long red cable running from the jumper post to the batt will act like an inductor for those spiky noise from the alternator and the long cable helps to filter the noise, and the batt acts like a giant capacitor at the end of the "inductor" cable and together they form an LC (inductive capacitor) low pass filter. So along the cable from alternator to batt, the noise of ripple or spiky waveform will be decreasing along this long wire toward the batt.

 

So with my 325ci same results this is with the car running

On the M3 with on the battery posts Vac is the same, kinda hard to take a picture since i gotta hold the probes with both hands.

But it's getting same Vac value about 29.8

 

Just to confirm, with your meter, both cars measure ~30VAC at the battery post under the hood and also at the battery in the trunk?

 

OP, use the DVM set to Vac and measure any 1.5v cell batteries that laying around the house to see if it shows zero or 20Vac. If showing anything other than zero then it's a bad tool.

 

Well i went out got a new battery.

I drove to my local Oriellys to get the new battery, I enabled voltage cluster test while driving and i noticed the voltage not too steady would see it jump around between 13.6-14.1.
So i swapped the battery, noticed that my radio LCD was fixed and i was able use the cabin dimmer on it. Before the radio stayed dim and would not change levels with the dimmer.
On my way home enabled voltage test on the cluster and voltage seemed more steady, i didn see too much movement and saw only stay between 13.8-14, pretty much steady on 13.9-14.

When i got home i decided to run another scan:

 # ERRORS DETAILS - DTC(hex)/PARAM(hex)
---------------------------------------------------------------------------------------------------------------------------
DME   ->  8F/C4 - Electronics-box fan
          8B/88 - Interruption, cruise-control system
          Shadow-memory:
          8F/C4 - Electronics-box fan
          8F/C4 - Electronics-box fan
          8F/C4 - Electronics-box fan
          DB/00 - Ox.sens.before cat. 2: signal excursion
          DB/00 - Ox.sens.before cat. 2: signal excursion

          Errors after clear:

          no errorsShadow-memory:
          63/00 - Internal fault
          59/00 - Internal fault

EWS   ->  0F/22 - Power on reset

          Errors after clear:

          no errors

ABS*  ->  5E5C/20 - RPA push button Error.
          5E5D/A0 - Brake_fluid_level low / Switch faulty.
          5DF7/A0 - Vehicle power > 18 Volt.
          5D97/A0 - Sensor cluster Supply voltage out of range.
          5DF4/20 - Vehicle power < 9 Volt.

          Errors after clear:

          5E5C/20 - RPA push button Error.
          5E5D/A0 - Brake_fluid_level low / Switch faulty.
          5DF7/A0 - Vehicle power > 18 Volt.
          5D97/A0 - Sensor cluster Supply voltage out of range.
          5DF4/20 - Vehicle power < 9 Volt.

LEW   ->  09/7B - No CAN message (ASC)
          10/87 - Watchdog

          Errors after clear:

          no errors

A/C   ->  1E/04 - AUC Sensor
          20/02 - AUC heating

          Errors after clear:

          no errors

SRS   ->  Shadow-memory:
          50/20 - Power supply, undervoltage

          Errors after clear:

          Shadow-memory:
          50/20 - Power supply, undervoltage

ZKE   ->  3D/0D - Central locking system: Short circuit or Open circuit at Motor Tailgate
          Shadow-memory:
          90/21 - Battery Voltage: Open circuit

          Errors after clear:

          no errorsShadow-memory:
          no errors

TEL   ->  6D/2A - E-call switch not connected
          6E/2D - E-call LED not connected
          80/2A - B-call switch not connected
          Shadow-memory:
          15/2B - NAD transceiver failure

          Errors after clear:

          no errorsShadow-memory:
          no errors

SZM   ->  Shadow-memory:
          05/02 - Seat heating Lower voltage recognised

          Errors after clear:

          Shadow-memory:
          no errors

SPMFT ->  05/22 - Mirror-heating interruption
          07/22 - Mirror drive, potentiometer vertical
          08/22 - Mirror drive, potentiometer horizontal
          09/21 - Mirror drive vertical interruption
          0B/22 - Mirror drive horizontal interruption
          Shadow-memory:
          02/02 - Low voltage mirror-heating

          Errors after clear:

          07/21 - Mirror drive, potentiometer vertical
          08/21 - Mirror drive, potentiometer horizontal
          Shadow-memory:
          no errors

SPMBT ->  Shadow-memory:
          02/02 - Low voltage mirror-heating

          Errors after clear:

          Shadow-memory:
          no errors

The ABS errors are no present though but they wont clear, on scanner software they have a yellow indicator.
Was searching those errors some people mentioned to drive it for while and see if they clear on their own and run the scan again.

Also looks like need to replace my e-box fan.

 

Were you running your Air Conditioner on your way to get your battery?

 

I measured the Vac at the jumper post on my 325iT, 0.2v using Fluke DVM.

 

I measured the Vac at the jumper post on my 325iT, 0.2v using Fluke DVM.

^This. Using a quality DVM is important so that false readings do not complicate diagnosing.