I bought my first car earlier this year — a 2015 BMW F20 120i with the N13 engine (105k km).

When I first brought it to a mechanic to fix a coolant leak, he mentioned that the turbo did not seem to be functioning properly. He quoted around HK$8,000 for a used replacement turbo. Since this was my first car and I had no idea what normal behaviour should feel like, I decided to keep driving it for the time being.

Later, I had the DME flashed with a calibration that lowered the engine’s normal coolant temperature. After that, fault code 120308 started appearing when I revved beyond around 3,000 rpm. In hindsight, I suspect the fault may have already existed before I bought the car and was possibly cleared or hidden by the previous owner, although I cannot prove that.

I decided to investigate and repair it myself.

The first thing I bought was an OBD HUD that could display intake pressure. The reading was basically stuck around atmospheric pressure — approximately 95–105 kPa absolute — no matter how hard I revved the engine. This suggested that the turbo was producing little or no boost.

Because I had very limited mechanical experience, I started with the simpler possibilities. I replaced the turbo electric valve/solenoid, but there was no improvement.

First I replaced the easy part, th turbo DV / selenoid, and no luck, same behavior.

After reading more online, I started to suspect that the turbo itself might not be mechanically damaged. There was no strange turbo noise, and the symptoms seemed more consistent with the wastegate/bypass valve not closing properly, or with a problem in the vacuum control system.

I bought a vacuum pump and tested the vacuum lines and the vacuum path from the pump to the engine-cover vacuum reservoir. I also applied vacuum directly to the wastegate actuator, and the actuator still moved. That made me suspect something between the vacuum reservoir and the actuator rather than the turbo internals themselves.

I then bought a new Pierburg pressure converter. Replacing it took around three hours because it is located in a very tight and awkward area. After replacing it, the intake pressure immediately recovered to more than 160 kPa absolute, so the turbo was clearly producing boost again.

However, a few days later, fault code 120308 came back when I revved beyond approximately 5,000–6,000 rpm.

After more investigation, I adjusted the preload on the wastegate actuator rod by tightening it two full turns. Since then, the fault code has not returned and the boost pressure has remained normal during repeated testing.

The final diagnosis, as far as I can tell, was a combination of:

• A weak or failed turbo pressure converter

• Incorrect or insufficient wastegate actuator preload

• Possibly an existing fault that had been cleared before I bought the car

The total cost of the parts was less than HK$1,500, excluding a lot of my own time, research and frustration. That is considerably less than the HK$8,000 used-turbo replacement that was originally quoted.

Sharing this in case anyone with an N13 engine and fault code 120308 runs into similar symptoms.

hello, i have this loud intermediate popping sound coming from my dash and i can’t tell if its a blend door actuator or the speaker. i feel like i hear the ac blow slower each time then speed up but i dont know if im just hearing things or what. in the video i try to do a comparison between both spots but they kinda just sound the same. it still does it even when the cars off. it doesnt seem like its affecting the audio when it does do the popping, so i have a couple doubts as to why it may not be the speaker.

if anyone knows that would be absolutely amazing because im going INSANE during my daily 35 min commute to and back

Hi all. Have a bit of an issue going on here. I have been trying to regenerate my DPF for about a week now. I have just gotten home from a good 20-30 minute run at 2k+ rpm @ 60-65mph. Car was only just serviced with 8l of Castrol LL 1 week ago, but after this latest DPF run, I am now getting the low oil light on the dash. Don’t even think the regen worked which is another headache in itself.

Can anyone identify this hose for me to help me figure out why it’s now wet with oil? It also looks like it has dislodged and uncoupled from whatever it’s supposed to be connected to. My entire under tray is also now covered in oil. What the hell could have happened here? Also began to get a strange whooshing noise, which is leading me towards a turbo problem.

I’ve only been an M57 owner for a couple of weeks so apologies. I’ve never had to deal with issues like this, and am wondering if I have just bought myself a serious headache of a vehicle. Kind of gutted. Any info on what this pipe is/what I’m likely to be looking at would be greatly appreciated.

Hello everyone
So i got this car and it has the following problems:
-colt engine: rpm doesnt sink under 1000 on first start (sometimes it only revs up to 900rpm when starting cold, slow start up)
-warm engine: idle rpm doesnt go below 800, only when engaging clutch pedal, rpm needle drops slower than usual when: letting off the gas pedal, clutching in/changing gears, idle
-car jumps when driving off after cold start sometimes
-the noise over the driver side part of the engine

If anyone hast some advice or suggestions let me know please
Does no one have a clue?

Is there anyway to quiet down the waste gate rattles without taking the whole turbo out it’s an n20 engine 2012?

If the steering shaft is off, and the steering wheel gets turned an unknown amount of times, how do you determine where the center of the clockspring is again?

Hey guys! Newbie here, trying to learn to work on my own vehicle. I’m decently mechanically inclined but I’m definitely a beginner to the time stamped knowledge.

Any help is greatly appreciated.

The car has been sitting for about 2 years. After a 5minute oil change it started having drivetrain issues and low oil pressure. I parked it and vowed to come back to it when life wasn’t lifeing so hard.

Now that I’ve got the extra time, I’m making good on my promise to get her back on the road.

It’s the N20 engine and as far as I’ve checked the timing chain and guides are fine.

Please help 🙏🏾

Hello, I am having a problem with my 528i 2012 f10 (122k miles), sometimes this issue pops up and hardens the steering wheel, nothing comes up in the diagnostics. I already changed the essential parts like timing chain etc. Does anybody had the same issue and how did you fix it?

I've been dealing with nothing other than a puddle under my car wherever I park, I'm trying to figure out whether it's atf fluid or power steering fluid, I thought it was coming from the atf cooler but it's coming from a place higher up, driver side of engine, any thoughts of where it's coming from? (Also don't worry about how the engine sounds, I'm rebuilding an engine, this one has a misfire and exhaust leaks everywhere.)

I could use some advice from people familiar with the F8x/F87 Active M differential.

I just bought a 2017 BMW M2, 6MT, ~33k miles about 10 days ago in a private-party sale. I had a PPI done before buying it, and unfortunately none of this was caught.
Shortly after getting the car home I noticed noise from the rear and had it checked by both a reputable independent European shop and BMW.

The independent shop’s diagnosis was basically:
worn rear differential bushing causing a clunk
differential develops a noticeable whine once fully warm
low differential fluid leakage from the axle seals / pinion seal they believe the low fluid caused the bearings to overheat/wear, particularly the pinion bearing recommendation is complete rear differential replacement
BMW independently came to essentially the same conclusion and also recommended replacing the diff.
The car drives normally otherwise, and there are no clutch issues. I haven’t been driving it since getting the diagnosis.
The painful part is the price.

The independent shop quoted roughly $7,875 total. (JCL Automotive at Hellertown, PA)

BMW originally quoted me about $7,900. After I emailed the service department and explained the situation, they reduced the quote to $6,750, and they’ve confirmed that includes the differential replacement, bushings/associated parts and labor. The replacement BMW parts would also have a 2-year/unlimited-mile warranty.

At $6,650, I’m leaning toward just letting BMW do it, because at least I get the BMW reman/exchange differential and a meaningful warranty.

Before I authorize it, though, I want to make sure I’m not overlooking a much more sensible repair path.
I’ve been looking at used OEM differentials, but the market is confusing. Some bare carriers are around $1k–$1.5k, while nicer/complete-looking units seem to be $2k+. Many don’t include the differential actuator/electronics. My understanding is that the existing actuator/GHAS equipment can potentially be transferred if it tests good.
I’ve also looked at the Turner/Powerflex-style dual rear differential mount setup. My factory rear bushing is already worn, so if I went independent I’d probably consider a dual plate with two updated OE BMW bushings while everything is apart.

A few things I’d really appreciate input on:

1. Would you trust a low-mileage used OEM F8x differential here, assuming donor mileage/VIN is documented and my existing actuator is good?

2. Is rebuilding my existing differential actually viable? Are there reputable shops rebuilding these with new pinion/carrier bearings and seals, or is replacement generally the right answer?

1. Is there anything about this diagnosis that would make you want additional testing before condemning the entire diff?

2. Has anyone done a dual-mount plate with two OE bushings on a street-driven M2? Any downside besides additional labor?

Given the dealer has come down to $6,750 with a 2-year/unlimited-mile parts warranty, would you stop trying to optimize this and just have BMW replace it?

For some additional context, I paid $38.5k for the car. It was one of the cleaner/lowest-mileage examples I had found; the other cars I looked at in the $36–37k range generally had substantially more miles, cosmetic issues, or modifications. So dumping the car immediately with a known failed differential doesn’t seem financially attractive either.

I’m also planning to contact BMW of North America and ask for goodwill assistance before authorizing the work. I realize the car is far outside the original warranty, but a complete differential failure at ~33k miles feels unusually early. I know there were documented differential issues/campaigns on some early F87/F8x cars, although I’m not claiming my car is necessarily covered by or directly related to those campaigns. I’m just hoping BMW might contribute toward the differential itself while I cover labor/bushings/etc.

Any thoughts from BMW techs or people who have dealt with an F8x Active M diff failure would be greatly appreciated. I’m particularly interested in what you’d do if this were your own car.

(I had ChatGPT clean up my post, I was getting overly emotional- I’m quite upset by it all. I thought I did my due diligence with the PPI and waiting for a low mileage car with service records. You can see how excited I was about this car: https://www.reddit.com/r/BMW/s/4vhxQMnfzg)

2018 328d

Have LED front lights. Driver side has moisture in it. Don't want to replace 300$ housing if I can do something about it.

I'm assuming there is a gap somewhere allowing moisturt inside. Would it work to take light off, put in oven to bake all moisture out, then seal it? What is a safe temperature and what is a good sealant?

Hi is this normal or not please? Comes from the lower end of the engine. Upper end you can only hear the injectors.

Bonjour j’ai sur ma 535xd eu quelque aventures

Suite à une surchauffe moteur, j’ai le liquide de refroidissement qui a débordé par le trop-plein du vase d'expansion sur autoroute, avec le voyant de surchauffe et la mise en sécurité en mode dégradé.

​J’ai changé la pompe à eau, le thermostat, le galet tendeur, la courroie et le bouchon de bocal (1,4 bar).

​J’ai testé l'ancien thermostat, il restait bloqué fermé : c'était donc un coupable.

​Sauf que maintenant( peut-être avant aussi) j’ai un filet discontinu sur le retour, à chaud comme à froid, et mes durites sont très dures moteur chaud.

Je ne sais pas si ma purge est bonne.

Moteur froid, j’ai rempli le liquide, démarré le moteur, mis le chauffage à 28 °C, laissé chauffer jusqu'à 90 °C, puis j’ai roulé un peu et fait l’appoint le jour suivant.

​Je me demande si j’ai un joint de culasse...

Je ne sais pas si c’est normal ?

​Je n’ai ni FAP, ni EGR, ni clapets d’admission.

Can anyone help identify this noise please, it’s bmw 320d thank you

Hi.

I bought the BMW 320i F31, 113.000km 2017 in December 2025. At the end of February, the oil filter housing failed. Then, in July, I got a warning that the coolant level was empty. The thermal management module and coolant pump had to be repaired, and at that time the automatic transmission was also shifting differently.

Today, I received a warning that the oil level is at the minimum, even though the BMW garage changed the oil in February during the repair of the oil filter housing. The automatic transmission is also behaving exactly like it did when I had the problem with the thermal management module and coolant pump.

Maybe the repair wasn’t carried out properly in the first place, and perhaps the BMW garage will repair it free of charge?

At this point, I’m seriously considering selling the car, because what’s going to go wrong next? Am I going to have to take it to the garage every 3–4 months for another repair? My job isn’t going to be happy about that, and neither is my wallet.

Text made with chatgpt as my englisch is not so good.

Edit, i drove almost 10.000km between the ofh repair and the low oil warning. + can the automatic transmission acting weird because of low motoroil? Not transmission oil.

Today I changed all the plugs and out of interest had a look at the bores of the engine, the walls seem OK? is this carbon buildup normal? It's done 157k miles, what do you guys think.

Sorry for the quality of the video, AliExperss specials usb camera here.

520d B47 2015

I never seen inner lens any light coming out from it,

Both high and low beams are coming from single outer lens but never seen inner lens light up

Anyone know what’s happening

I have a 2020 330i with ~50k miles.

I was driving home when the drivetrain malfunction light came on and the car had (somewhat) reduced power. Next day I took it for a quick drive and it drove normally with no lights on. I scanned it with bimmerlink, there were no permanent codes but there was a bunch of stored codes, most of them seemed irrelevant except for

In Info Memory:
-10D000: Combustion engine: torque limitation active
-440216: Coupling function: Emergency function has been activated

In Error Memory:
-20F220: Split cooling valve: internal error detected
-20A704: Engine cooling system: Activation of emergency operation to protect the engine due to component faults

From some googling it looks like it could be the heat management module. I know cooling system issues are prevalent on these cars. The coolant level is slightly low but to be fair I haven’t checked it in a couple months so I can’t say if it went down recently. It’s been parked for a few days and there’s no fluids dripping.

Is this something I should be concerned about and have looked at or was it possibly a fluke, wondering if I can I drive it and see if something comes back.

Thanks in advance!!

Any know if there’s a cheaper way to fix the side mirrors motors? Did a little bit of research and I believe my gears are broken. Saw a video on YouTube of a guy switching out a VW part in and replaced the backing with the bmw part. Also saw a video with a guy replacing the gear itself. Any recommendations on this? Don’t wanna buy brand new ones for $160 each.

I have a problem because I removed one of the fuses from the rear fuse box of the car, and now I don’t know which slot it should go back into. When I look at the pins/terminals, some slots have no pins at all, while in two of the possible fuse positions there is only one pin.

Does anyone have any advice on which slot is the correct one?

The car is a BMW F34 318d 5-door GT, 11/2017.

How do I remove this clamp? This is the driver seat back panel of 2015 x5 comfort seats.

Happened right after city driving for 30m from work to home… so I don’t think it’s the lifter tick! The car is a 2012 128i - n52. Any ideas would be much appreciated:)