Hey all,

I have a 2013 GLK 350 and recently had an electrical issue (that I found to be the Prefuse F32 box overheated) and now that it’s fixed. I have the RF ABS speed sensor fault, which has the ABS, stability control, cruise control, and ECO start disabled. The main problem that came about, is after approximately 3000 rpm, the car abruptly nose dives and there is no power response, just surging. I pulled it over into a parking lot and put it in park and it surge idles from 1000-1500 rpm. An engine shut down and restart clears this and I can resume driving, so long as I don’t go over 3000 rpm. I replaced the batteries during troubleshooting the electrical problem (they both load tested bad) and now have this issue. I saw some searches saying a security limp mode at 3000 rpm while driving. Is this due to me changing the batteries and needing to reset in the system? I do have a new wheel speed sensor on the way. And I do have an iCarSoft MB 2, if needed.

Any and all help is greatly appreciated!

 

I don't think it's from the batteries, but if they were original it's probably a good idea to replace them.

It could be the wheel speed sensor, per the scan tool, but if replacing it doesn't fix it you might want to research "reluctor ring" replacement. Seems quite common to fail on the rear axle.

Keep us in the loop, and I'm sure others will chime in.

 

Ok, thank you. I did try disconnecting the battery for an hour, then doing the synchronization of windows and steering, but no change. Hopefully the sensor is the problem and the system doesn’t want excessive power from the engine without the stability control. Otherwise, I’ll be digging into the front right hub and replacing a bearing.

And the batteries were 3 years old. F32 panel had overheated where the output post to the battery is and melted the plastic. That caused a dielectric effect on the bus bar inside F32 and severely hindered the alternator-to-battery. That in turn caused the alternator to create a flickering effect in the lights, since the battery was not able to dampen as well. I’m wondering if that caused a problem with the sensor and (more or less) fried it. 🤔 I’ll post back tomorrow evening with an update, once the new sensor arrives.

 

Great news! Not only did the speed sensor come in today, it also cured the “limp mode” after 3000 rpm. Now my GLK is running like it was designed.

 

I like a story with a good ending. Congrats on the repair and thanks for following up with the fix.

 

I wasn’t sure if the sensor itself was bad or loose connection, only because the problem would go away for about 5-10 minutes then come back, then off, then back on, etc. I pulled the connector in the wheel well and checked that, slightly moved the pins (in case of poor connection) then checked the wiring on the engine bay side. It comes out between the battery and F32, which made me wonder if it was compromised during a battery change. All of that was ok, so I bought a replacement. I see the drivers side is the same part number, so I could have used that to see if the problem followed. I’ll leave that tip for anyone with this problem in the future 😉.