[REP663]

This happens when I accelerate hard, usually starting from highway speeds. No code is generated and the CEL resets when I shut off the engine. On-screen message says the engine is operating with limited power, but that's clearly not the case.

How do I find out what's wrong? Why is no code generated? Thanks.

 

[Doug Huffman]

That no DTC is stored is unlikely.

 

[REP663]

That no DTC is stored is unlikely.

Well, it happened this morning and I took it to my indy while the car was still running and the CEL still displayed on the dash. He patched his reader in and saw no codes. I'll check back with him to make sure his reader can detect all the proprietary BMW codes, but I would think it could, given his customers.

Also, is it unusual for the CEL to reset on its own?

Thanks.

 

[HotGrbg]

Check engine lights throw codes. I’ve rarely seen ANY cars with “no codes” check engine light or not. I suspect his code reader can’t read BMW codes properly.

 

[plus1111]

Was the light a half-engine image? That's a bit different than check engine. Most likely the only code will be something about reduced boost. Are you running stock?
By the way, I am fighting the same thing and it won't do it when I want it to.

 

[HotGrbg]

3100 boost pressure deactivation is not a 1/2 code. It’s set and stored like any other code. 3100 however is not the causal fault but a symptom of another problem which will set a separate code.

 

[plus1111]

I dunno HotGrbg, I've been chasing it for a couple of years on our 535xi. It leaves one code, 30FF. There are no other issues. I've replaced vacuum lines for the turbos and checked the linkages. All the dump valves operate properly and seal. 30FF is the code I see every time. I'll find it one of these days. It doesn't happen regularly enough to be a big issue as yet. I can allow a few hissy fits at almost 250,000 miles I guess.

 

[HotGrbg]

@plus1111
30FF is underboost. It means your wastegates are failing or your not supplying proper vacuum to the actuators. Simple diagnosis here honestly. Measure vacuum directly at your wastegates and you should see around 15hg. If you have proper vacuum then your wastegates are worn and your turbos are shot. This is usually apparent with a wastegate rattle on deceleration and also seems to show up mostly when it’s hot outside and air mass is lower compared to cool dense air. If you would like to confirm this then you need to remove your cats and pump your wastegate actuators to 15hg and try and rotate the wastegate sealing doors. If you can turn them then they are too loose. Also you can look at the wastegate seats and see if the sealing doors are sitting flush against the turbo housings. On an 08 535 with 30FF I’d probably wager a small bet your turbos are failing.
If your vacuum is too low you could have collapsed vacuum lines, failed EPDWs or a vacuum leak.
3100 is boost pressure deactivation which is consequential of many other drivetrain codes including the 30FF.

 

[pshovest]

.....Also, is it unusual for the CEL to reset on its own? ....

It's not unusual at all. Misfire codes in particular will clear CEL on restart, particularly if the misfire is not present on restart and is only a high RPM/engine load event.
It's important to scan while CEL is lit. Drive in a fashion that turns on the CEL and without shutting engine off drive to Autozone and try their scanner.