[Shadows335i]

So I have a 2010 e90 335i, voltage regulator failed car was spiking 20 volts got it home and let it sit, got a after market (off brand) regulator from a local automotive electrician shop cause i needed the car. First voltage regulator was fine for a few miles but was fluctuating between 13.5 and 14.5 volts and momentarily spiking 17 volts (causing the car to spaz out), also started throwing ibs codes (ibs missing) and water pump codes (missing, limp home mode).the wire to the voltage regulator also seemed like it was really twisted up but left it alone and tried to set it back the way it was. Turned around and ordered a Bosch vr from fcp euro enter vr #2 car is still randomly spiking but voltage is settled between 13.6-13.9 (2 month old battery that was bench tested after original over voltage situation and came back good 3 separate times) car went about 50 miles before randomly starting to spike but this time it's only going up to 16.5 momentarily. This is when I start noticing that it's doing over bumps. No water pump codes but still getting ibs codes so I replace the ibs cable (negative battery cable and ibs sensor) recode the battery and it stopped for a few miles. Then it starts doing it again, now I'm not having battery discharge issues so I take the car into one of my bmw indy shops and have them go over the grounds in the car and inspect everything. Car comes back with good grounds and everything looks OK so they diag it as a defective vr. Fcp euro sends me a new a new vr and I'm rather meticulous while installing this one I take the CAN wire to the vr pull it from how its originally routed un twist it (cause it seems really kinked) and route it away from the bottom of the alternator more in the space above the hpfp as to not let it make contact with anything. Plug it in reprogram the battery and take the car on a nice drive. 150 miles no issues and voltage is between 13.9 and 14.1 with very little fluctuations. So I'm thinking ok defective vr problem solved. Nope. Hit a bump just right and it spikes. So now I'm thinking ok it's gotta be the alternator. Pull the alternator out and have it bench tested, comes back as being fine steady 14.3 volts for a total of 4 hours (under load and at idle). After talking to the shop that did the bench test and looking around on the forums here, I'm gonna try two things. Create a new ground strap of the chassis to the motor to see if that's the culprit (press x for doubt) or create a jumper wire from the vr to the the dme to see if it is a bad wire, I know that wire also goes to the oil condition sensor so im not gonna brake the chain of communicationbut i plan on adding a wire directly from the vr to the dme. Any input or experience with this?

[Tambohamilton]

Alt, water pump, IBS and oil sensor are all on the BSD line (LIN bus), and if one freaks out the lot get affected.

To me it sounds like the dodgy wire to the alternator is causing the issues. But it could potentially be anything else on the BSD line causing things to freak out (I doubt it).

[Shadows335i]

Car isn't throwing any bsd codes after replacing the ibs sensor, how ever put the alternator back in and got it all wired up but I do actually believe that this problem might be stemming from the frm considering that it's been acting wierd the last few weeks since the original issue and now that it has complete left the chat.

[JimmyV12]

Originally Posted by Shadows335i

Car isn't throwing any bsd codes after replacing the ibs sensor, how ever put the alternator back in and got it all wired up but I do actually believe that this problem might be stemming from the frm considering that it's been acting wierd the last few weeks since the original issue and now that it has complete left the chat.

Did you solve the issue? Having similar problems

[ChuckW]

I purchased a Bosch voltage regulator from FCP as well. It fit and was shaped like the OEM, but the heat sink was made of plastic. It caused similar problems as what you mentioned with varying voltage and obnoxious spikes. I know they're selling it as the correct part, but it wasn't.

I had changed mine thinking it was an easy piece of preventive maintenance. As soon as I reinstalled the original one, everything went back to normal. Honestly, if I had changed it for a failed regulator, I would never have suspected the new regulator was bad (or the wrong part).

Other suppliers' websites offer the correct voltage regulator with the metal heat sink. There's a major cost difference, but still so much cheaper than a new alternator.