X5 35i N55 Engine Malfunction Reduced Power Charging Pressure Too High

[ltemup4650]

All, I’d love to hear your thoughts and input with this issue.

There are several threads in various forums like the one I’m posting. All too often, however, folks (original posters) don’t circle back with their resolution. Thus, I am creating my own detailed post and I promise to return once the issue is resolved. As stated, this will be a detailed post and I’ll go through each item in a support/refute style troubleshooting plan.

Vehicle: 2011 BMW X5 35i E70 with N55 turbo inline 6 cylinder engine. 86,000 miles.

Codes:
002C56 – Charging pressure control, plausibility Pressure too high.
002C58 – Charging pressure control: Switch-off as consequence*
*this code is set as a result of the first code. Pressure is too high = DME shuts off the turbo for protection.

NOTE: No check engine light. Just the half engine warning with “Engine Malfunction Reduced Power” fault warning.

How I can set the fault: Moderate throttle over time. Example: driving on a long interstate on ramp, slightly uphill, constant 50% to 75% throttle.
How I can avoid the fault: Light driving around town, or the opposite: WOT for a significant distance and then letting off the throttle.

I will note that I actually have two 2011 X5 vehicles. The one without the problem has 135,000 miles. The one with the problem has 86,000 miles. Both are the 35i with the N55 engine, thus, I have the luxury and ability to swap parts one by one until the issue goes away. This said, I’m not a “throw parts at it” type of guy and would prefer to properly diagnose. Swapping parts is time consuming.

Potential cause: WASTEGATE ON TURBO
Why it might be this (support): If the waste gate is stuck closed, exhaust would not be routed around the exhaust turbine of the turbo, thus creating boost all of the time.
Why it might not be this (refute): Reaching down with my hand, I can move the linkage back and forth. Also, when the engine malfunction and reduced power warning comes in, I can tell the boost has been stopped. Thus, the wastegate moves. N55 wastegates don’t fail near as often as N54 wastegates.
What I’ve done/plan: I will need to try this on my known good X5 and note any differences in feel.

Potential cause: ELECTRONIC WASTEGATE ACTUATOR VALVE (Boost Control Solenoid Valve - 11747626351)
Why it might be this (support): Of the forum posters that return to report their fix, this is the most common part. It is plausible that the solenoid if getting weak and not releasing the air pressure fast/well enough.
Why it might not be this (refute): The N55 keeps the wastegate normally open, and only actuates when boost is requested. Thus, since I do get boost, it will pull the wastegate closed. If this is the cause, it is a soft failure as it appears to work most of the time.
What I’ve done/plan: I ran the ISTA test plan for this. The linkage was observed to move, however, it didn’t appear to move much. That said, I don’t think the test plan had me run the engine. I would think it would want me to run the engine so is had vacuum (motive force) to move the wastegate.

Potential cause: VACUUM LINES (to and from the Boost Control Solenoid Valve)
Why it might be this (support): Vacuum lines could be clogged/degraded/pinched affecting the operation of the pneumatic actuator that is the direct operator for the wastegate.
Why it might not be this (refute): The wastegate will operate. If the vacuum lines were degraded, one would think the wastegate would stay in its normally open position. A low boost trouble code would be more likely to set if the vacuum lines were degraded.
What I’ve done/plan: need to inspect the vacuum lines

Potential cause: PNEUMATIC WASTEGATE ACTUATOR (the vacuum actuator that is actuated FROM the boost control solenoid)
Why it might be this (support): This valve could be sticking and not letting the wastegate open in a timely manner.
Why it might not be this (refute): I ran the ISTA test plan for this. The linkage was observed to move, however, it didn’t appear to move much. That said, I don’t think the test plan had me run the engine. I would think it would want me to run the engine so is had vacuum (motive force) to move the wastegate. Also, without the engine malfunction reduced power fault, I do get boost. And with the fault, I don’t get boost. It works, maybe it is just a soft failure.
What I’ve done/plan: I ran the ISTA test plan for this. The actuator worked moves.

Potential cause: EXHAUST CONTROL VALVE
Why it might be this (support): Too much backpressure could affect turbo speed and thus boost.
Why it might not be this (refute): I ran the ISTA test plan for this. The actuator worked and exhaust note changed.
What I’ve done/plan: I ran the ISTA test plan for this. The actuator worked and exhaust note changed.

Potential cause: “BLOW OFF” / DIVERTER VALVE
Why it might be this (support): If the diverter valve does not divert in a timely manner as the throttle goes closed, this could cause extra boost.
Why it might not be this (refute): When the engine malfunction reduced power fault comes in, it isn’t when the diverter valve should be diverting (i.e. I have constant throttle when the fault comes in).
What I’ve done/plan: I’ll test and explore other more likely components before I get to this.

Potential cause: MASS AIR FLOW SENSOR
Why it might be this (support): If this sensor is bad it could cause all sorts of boost/air mismatch problems.
Why it might not be this (refute): If this sensor was bad, it would probably have its own specific codes and a check engine light in addition to the engine malfunction reduced power fault warning.
What I’ve done/plan: I’ll test and explore other more likely components before I get to this.

Potential cause: MANIFOLD AIR PRESSURE SENSOR(s)
Why it might be this (support): This (these) sensor(s) could reading the manifold pressure incorrectly. If so, the turbo and all of its control components could be working just fine and the sensor is falsely cutting it out due to the incorrect pressure reading.
Why it might not be this (refute): If this sensor was bad, it would probably have its own specific codes and a check engine light in addition to the engine malfunction reduced power fault warning.
What I’ve done/plan: I’ll test and explore other more likely components before I get to this.

Thanks for reading and providing any input you might have.

[ltemup4650]

UPDATE: Re-ran the ISTA test plan with the engine running (ISTA did in fact call for the engine to be running, it was late and I must've misread the instructions). First off, when I fired up the engine, I could hear "whoosing" in the intake piping. This is not normal. Looking at the wastegate, it was closed at idle with no accelerator movement/command from me. When running the ISTA test for wastegate actuation, the wastegate barely moved. When I stopped the engine, the wastegate fully opened. This leads me to believe that the pneumatic actuator and wastegate itself are fine, and that the electronic actuator has failed (i.e. it is leaking by and allowing the wastegate to close all of the time). I will be replacing the boost control solenoid and reporting back soon.

[ard]

In case the above doenst fix it...
Is your AFR all spot on? So MAF, map and O2 sensors? Also and VANOS issues? Oil changes regular, no chance a solenoid is fouled/needs cleaning?


If a DME gets into a weird air/fuel map, say at partial throttle/load, it can do odd things with boost commands...

FWIW

[ltemup4650]

SOLVED

Thanks for your input ARD.

I replaced the boost control solenoid and it works as it should now.

Here is a video I made on it:
https://www.youtube.com/watch?v=67WGhkZaPts