No fault codes, but intermittent power loss between 60 and 70 mph in my BMW 420i Gran Coupe.

[Alex1978]

Hello everyone! I was hoping someone could give me some advice based on their experience with a BMW.
My BMW 420i Gran Coupe is a 2014–2017 model with 76,806 miles and a manual gearbox.
I've been driving steadily at 60-70 mph on the highway when all of a sudden the power goes out for about half a second. Then it comes back on and drives normally, which is a really strange and intermittent problem.
There has been no slow dwindling of strength. For that brief instant, it's as if the vehicle becomes unresponsive. At that second, the speed won't increase no matter how firmly I plant my foot on the floor; then, out of nowhere, the power returns.
To try and find a pattern or rule anything out, I've experimented with various gears, driving modes (Comfort, Sport, and Eco Pro), and cruise control, but it doesn't make a difference. Up until this point, it has only happened to me on long car rides, and it seems to happen at random.
The fact that it happens so randomly is the most annoying aspect. It occurred again on Saturday after the previous occurrence about a month ago. The ECU is not displaying any error codes, warning lights, or discernible pattern.
German Auto Center has since performed a comprehensive diagnostic and health check on the vehicle that I had scheduled. There are no error codes to guide them, and they still haven't discovered anything wrong with the vehicle.
Even with real-time data, it's very challenging to diagnose events that occur half a second apart, let alone weeks apart. Not knowing what's causing it makes it seem like a needle in a haystack, and I'd rather not start spending money on replacing parts.
Is anyone else's BMW 420i or other petrol 4 Series dealing with something similar? Were you ever able to determine the root cause and the method of diagnosis?
I would love to hear from anyone who, while driving on the highway, briefly lost power without any lights or codes coming on, and what the solution was.
Even though it's brief, the fact that it occurs at high speeds on the highway makes it all the more worrisome because of the danger it could pose.
I would be eternally grateful for any help or insight you could provide. I'm crossing my fingers that someone will be able to identify these symptoms and give me some advice. I am grateful.

[dave783]

It probably goes hand-in-hand with using the windscreen wipers, right?

[Alex1978]

Yeah, that's right.
Whether it's a coincidence or not, we've never had this happen on dry trips. However, it usually rains right when it does, so they're on.

Whether it's weather-related or not, I can say with certainty that it hasn't happened when it's been dry.

Are you not aware of the solution? 😁

Much obliged for your prompt reply!

[Rashman4u]

It has to do with maintaining dry brake pads when driving in rainy weather. I would say it's typical. Just look it up on Google.

[Alex1978]

We've had the car for five years, and this has never happened before.

Do you think it would be noticeable?

[IrvesBMW]

The same thing happened to my F32 420i N20, too.

No, that is not the brake drying performance. You hardly notice when that one brushes against the pads.
The brief power cut that you're describing is actually the vehicle's brakes.

On N20, one of these three things happens almost every time:

1. The Classic N20 problem is causing HPFP to begin failing. You experience a split-second cut when it becomes unable to maintain steady cruise pressure.
Do not enter any codes until the situation worsens. Using ISTA, verify the readings of your low pressure fuel sensor while you're on the road.

Your ignition coils and spark plugs are due for replacement at 76,000 miles. A weak coil will misfire for one combustion cycle under light load at highway speeds, and the DME will cut power to protect the cat.
It occurs at such a rapid pace that no code is recorded. See if it follows by switching the coils around the cylinders.

3. Wastegate actuator / charge pipe – A small boost leak won't be noticeable until you're cruising steadily at 60 to 70 mph.
Upon detecting boost deviation, the DME briefly cuts throttle.

With the wipers turned on, which means it's raining or cold, I'd be surprised if it wasn't the ignition.
A cracked coil boot can arc if moisture gets inside.

Carry out this task: While you're behind the wheel, have someone record HPFP pressure and misfires using Bimmerlink or ISTA.
As soon as it occurs, I wager you will notice a drop in pressure or a misfire count.

Put the pieces aside. Record it initially.
Please inform me of your findings; I am an expert on N20 gremlins, haha. 💪🏻😊

[Alex1978]

I am truly grateful for the guidance you have given me. My only option, aside from taking it to a garage, is to not have ISTA or know anyone who does.

The diagnostics performed by German Auto Center did not reveal any error codes. It can go weeks without occurring, and when it does, it lasts for only approximately thirty seconds due to how intermittent it is. I'm concerned that I might wind up paying a garage an hourly fee to attempt to catch it, and there's no assurance that it will happen during their testing.

Equally unsettling is the idea of starting to replace components based on pure speculation. Based on your expertise, what do you think would be the best course of action for me to take next? How can I keep track of the necessary data without paying for expensive road testing? Is there anything in particular you think a BMW expert should look at?

In particular if you were unable to obtain fault codes, I would be very curious to hear about your experience in resolving this issue if you have encountered it before. Thank you once more! 😊

[dave783]

It is possible for the brake drying feature to malfunction, in which case it applies more brake pressure than intended and fails to produce any detectable trace when scanned.

It seems like the DSC module could be at fault if you can observe if it only happens when the wipers are turned on.

Three different repair choices

1, get a new DSC 2. have the old one repaired
third, have a code brake dry out expert (with knowledge of mapping, etc.)