Car Owners Hub UK - Built by Drivers, for Drivers

I am experiencing some electrical problems with my 2011 E350 CDI. Both EML and limp mode appeared out of nowhere. It shifts gears forcefully at about 2,000 revolutions per minute and drives extremely flat (with no boost).

Car scanned and returned the following code:
Situation: Present and Past

Subsystem Y77/1 (Boost Pressure Positioner) Is Ground-Circuit Shorted.

At first, I blamed the actuator's internals, but I decided to test it out first before tossing out the parts.

Here is what I have discovered:
When it should be around 12 volts, the voltage on pin 1 is only around 1.4 volts.
It appears that the 12v ground on Pin 2 is valid.
Again, pin 4 appears to be connected to the 12v ground.


So far, everything appears to be in order, however at first I wondered if there was a slightly cracked wire or rust on the continuous 12v cable.

I proceeded to check the Sam module's fuses, and they were all found to be fine.

During my testing, I came across two intriguing aspects.

1) The actuator constant live pin reads 0 volts when the swirl flap motor is unplugged, but it reads 1.4 volts when the motor is connected.

2) There is a jump from 1.4 volts to 2.5 volts on the actuator's pin 1 when I disconnect bank 1 of MAFs.

I was hoping to stay away from the parts cannon at first, but I ended up purchasing a new actuator that didn't fix the problem.

Please, someone, tell me what other tests I should do to determine the source of this problem.

I believe It is possible that SAM is bringing all of those components online at the same time. The system detects a short circuit and disables full voltage, the constant feed is unable to generate a high enough voltage, or the resistance is too high. Check the fuses are in good working order and see if you can test the resistance across the wire; I recall an incident when a blade fuse was partially blown, meaning it had continuity but wasn't passing enough current; miraculously, it didn't burn the remaining contact either.

Much obliged for your response.

See what I find out when I measure the resistance across the wire. In addition to the standard continuity test, I double-checked that the voltage on each fuse was close to 12 volts.


Currently, I'm considering purchasing a new loom to experiment with.

At least on my W212 Om642, I experienced the same problem after removing the turbo actuator, flap motor, and MAFs. The under-hood fuse board had number 22. Replaced fuse; regular servicing has resumed. Of course, it could be completely wrong.Recommendation only.

On these vehicles, I've found that the code reader's "short to ground" indication is often completely inaccurate.The item is not receiving power due to a blown fuse, a lost plug, or something similar.

I have encountered situations that are comparable, such as a short to ground or an open circuit?

Your recommendation is greatly appreciated. Since you changed the fuse, has your automobile been running well, or is it still blowing fuses? It would be wise for me to examine that fuse twice or even three times in case you experienced the same issues. If I have a few minutes tonight, I will likely do this.

One typical cause of blown fuses is malfunctioning swirl flap motors.

What code reader did you use?

Ever since then, everything has been well.

Two code readers are at my disposal: the dependable iCarSoft and the brand new TopDon. I'm going to double-check the fuses just in case.

I've fixed the problem, however I'm not sure whether I can mark this thread as resolved.

Everyone who contributed smart suggestions has my gratitude. Every single one of your comments is spot on, and I'm sure they'll help someone else out in a similar situation. In my instance, the intermittent live signal from the swirl flap motor plug was caused by a partially severed wire. I fixed it myself for the time being, but I'll get to the real fix later on.


A decent used loom is actually something I'm thinking of getting. The socket for the map sensor is covered with oil, as I've observed. Alternator LIN wire repairs have been necessary for me in the past. Multiple repairs on a loom aren't my thing. I could get by with only one or two fixes, but I'll need to fix all three of them after I replace the connector on the map sensor.