Kal Sahoo

Hey everyone!
I have a 2008 550i Msport, that has been having this problem for around 2 months. Earlier, it would reset to normal with a simple restart. Then going into the colder weather, It started happening every cold start, and wouldn't return to normal with a restart. I would have to let the car sit after running for around 20 minutes. Now, it won't come out of limp mode.
Today (and also before when the problem first arose), on the highway I received:
DBC Malfunction!
Start Off Assistance Malfunction!
Engine Malfunction!
EML on

I pulled codes P0120, P0221, and a pending code, C0300.


I replaced the Throttle body harness (Part #: 12 51 7 602 973) and it did not seem to fix the problem as others have stated.
All fluids are topped off as well.
AFTER the repair:
With the TB plugged in, the engine was still in limp mode, although did not limit RPMs.
With the TB unplugged, the engine limited RPMs to 1900. So from what it seems, the harness is wired correctly (i triple checked!)
The next place to go is the throttle body, from what i've seen.

I have searched, and although i am experience what some others witih the same problem have experienced, I don't know where to go from here.
A refurbished throttle body is 280+tax from autozone, and I will need my car fixed ASAP!
Does this sound like a TPS problem? or does it seem intermittent?

would like to get others opinions on this, and can provide further information as well.
Thanks! ~Kal

Jim165

I just recently (3 weeks ago) fixed my car after suffering through the exact same thing. I replaced the throttle harness, throttle body (be sure to get an OEM one, not a refurb), alternator and battery. Still didn't fix the problem, gave up and took it to an independent. It took him a couple hours but he eventually rechecked the throttle harness, rewired it and had to do a DME reset. That's cured it and the car is running much, much stronger than before it started malfunctioning.
You can get a brand new OEM VDO throttle body for the same price as that rebuilt one:
BMW Throttle Body Assembly - E53 X5, E60 545i, E63 645ci, E65 745i w N62 Engine

seanjordan20

I have never heard of this issue before. It is surprising to me that 08s are needing a TB change so early. Those usually do not go out at least within 10 years 200k miles.

Kal Sahoo

Thanks! How do i perform a DME reset? Is it as simple as disconnecting the battery for 30 mins - a couple hours? I tried unplugging the battery from the negative side, waited 20 minutes, and restarted to no avail. Any other tricks I can try?
I have a new TB and Pedal assembly on the way. Will return whichever doesn't need to be replaced.

Jim165

Sean, this is actually a pretty common problem on the N62. Just do a search on the X5,5,6,&7 boards for "throttle body"...basically any car that uses the N62. The only thing this throttle body has to do is keep the flap open when running and it fails to do that basic function after awhile. Well, it actually acts as a throttle backup if Valvetronic fails, so I guess it's doesn't just have a basic function, lol.


DME reset requires something like INPA or some other dealer/indy software as far as I know. Just unplugging the battery ain't gonna cut it. You could possibly have the throttle body harness wiring mixed up as well...turns out it is not a direct install because you could have the wire/pin combination mixed up. The repair harness wires and the wires coming from the DME don't have matching colors (which is stupid) so mixing it up is easy to do. I'm betting that is part of your problem...that was definitely mine. A quick test is to check the function of the throttle body after you put the car into "run" (ignition on but not started). I think the throttle body flap should open after a couple of seconds. If it does nothing, there is no communication from the DME to the throttle body or the throttle body itself is bad, causing the limp mode.

Kal Sahoo

Yes!! The wire colors pissed me off! Although i did match them from the original pins. (matched each pin). I'll give the throttle body test a go and let you know how that goes!

seanjordan20

I never knew. Something so premature I would talk the dealership in replacing under the good faith warranty. The many times that have saved me from spending a lot of money for something that should not of failed so early. I hope you get things worked out.

Kal Sahoo

Ok. I've replaced everything i can think of being the problem. Pedal assy, as well as TB and the TPS harness. When i start ignition, i can hear and see the throttle body open and close. I cleared all codes but nothing has changed, now it's just in limp mode!

I honestly don't know what else this could be! any advice?

Jim165

I think it's time to take it to an independent. Have you noticed the voltage as it's running? seems like you could possibly have problems with voltage. How many miles are on the car? The alternators are the other source of problems on these cars as any little deviation of a steady 14 or so volts will cause a lot of things to go haywire. There is a way to access the voltage in the hidden menu in the dash (you'll have to google it). Anything less than a steady 14-14.6 volts while running and under load will point to the need for a new alternator and possibly battery.

I'll tell you how coincidental your post is:
After running perfectly and strong for the past 3 weeks after repair, I encountered a "soft" limp mode....no CEL but power was lost with almost no response to throttle. A restart cleared it instantly. It happened 2 more times and last night, it threw a CEL with the half-engine fault and reduced power. It wouldn't' reset after a restart this time and there was a loud hiss/squeal coming from somewhere under the hood. Had the exact same rough idle and surging that started all of this crap. I had Carly app hooked up this time while it was running and voltage was all over the place. I had my old alternator rebuilt instead of replacing with a new one before all of this happened a month before and I think the voltage regulator isn't working right. Already set up an appointment with my indy for a new OEM alt install as he thinks that is the problem ($1000).
Long story short, check your voltages and see if they are a steady 14.6 or so. If not, that could be the cause of the limp mode. Just throwing out another possible issue to check, but I by all means hate encouraging throwing parts at problems like these. I'd get an independent to look at it and fix it once and for all. Good luck.

Kal Sahoo

I checked the voltage, it seems to be running around 14.6, and never drops below 14.2, and highest i've seen is 14.8 under full rpm.
I also tried connecting my father's M4 via jump cables to get a more steady current, but nothing.
I agree, it is time to take it to an indy. I'm able to drive the car now, it is just slow and stuck in limp mode!
Anyways, will be taking it in ASAP (most likely monday) will let you all know how it goes!