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Discussion Starter #1
My dome light was working fine a few days ago but now stays on when both of the doors are shut. I searched the forums to see if I could find a way to troubleshoot the problem and found a lot of discussion regarding a part found behind the spare tire called the PSE. However, it seems I should start by checking the door switches. Problem is, I'm not exactly sure how to check them to see if they are still working without just replacing them. Any ideas?

Also, for background, I recently replaced the trunk struts and also a bulb in the dome light. But the dome light worked fine for a couple of days after doing both.

Much appreciated!!
-L
 

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Discussion Starter #3
Thanks MrG. I hopped in my car to drive to work this morning and noted two recent developments in the saga. With my doors shut, I hit the lock doors button on the console and it no longer works. It unlocks the doors still, but won't lock them. I do this every time I get into the car, so this is new as of this morning.

Also, the trunk stays locked now even if the doors are unlocked. So I now have to unlock the trunk with the keyfob switch from outside the car. This is getting weirder and weirder. I'm new to working on my car so this is all a mystery to me that I can hopefully solve.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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pse pump right woolly?
 

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Hmmm. Seems to be a bigger problem than I was hoping. The Check Engine light just came on. Would that be triggered by the PSE pump malfunction too, Jeff?
 

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well, i am not the r170 guru and woolly always says the pse pump just handles 'vacuum' things, like locks, etc. someone hopefully will jump in
 

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Another odd symptom occurred while I drove to work this morning. After driving only a few minutes at about 20 miles an hour, a loud two-tone beeping alarm sounded inside the car. I've never heard anything like it. It wasn't the theft alarm, nor the horn. It was electronic sounding. It continued for about 30 feet and stopped as I pulled over but before the car came to a stop.

If this is, along with the other symptoms, caused by the PSE pump's failure, then I would feel comfortable replacing it. But it may be something more than just the PSE pump. And if so, I think I'd want to take it in to a mechanic. Any ideas?

Thanks for your thoughts!
-L
 

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PSE is located behind the jack. It's where the yellow lines come out in this pic. Those are the air lines coming from the PSE.

Check for any sign of moisture or water damage.

 

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Thanks MrG. I just got the car emissions tested -- required in WA for tabs -- and it failed. The code is P0410 secondary air injection system. Sounds like some kind of air pump. Could this also be linked to the PSE pump? If so, then it seems like the constellation of issues I'm having are at least related to one big expensive problem and not a series of big/small expensive problems. :p
 

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I had random locking issues, alarm going off etc, and was directed to the PSE unit, but it turned out that I just needed to clean the contacts on the door microswitches. Check all the tiny issues first, the PSE unit is an expensive option.
 

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Discussion Starter #11
Update on status: WA state will give you a waiver with respect to a failure of the emissions test if you go to a certified emissions specialist and spend at least $150 trying to get it fixed. They give you a list of such specialists. Unfortunately, none of the mechanics recommended on this site are on there. So given the timing, I took it to the Benz dealer. They performed the B-service it desperately needed and told me that the car needed the following:

1. Dome light, console lock switch, trunk lock - PSE unit is bad. They checked all the microswitches and wiring prior. They offered to replace it for $2,500. Ouch. Needless to say, it's not getting replaced at the moment by them.

2. Emissions issue - all of the hardware was fine, they said it needed a software update. So they reset the computer and fixed that problem. Done.

3. My dash lights were out - they went in to change the bulbs but they were fine. Said the circuit board was going bad and would replace it for $1,200. Too expensive for the moment.

4. Fan belts - apparently two of my fan belts were cracked and about to fall off. They have replaced them.

5. Motor mounts - I noticed the idle was rough on my car. They said that one of the hydraulic motor mounts had leaked all of its fluid out. They offered to replace it for $820. Not doing this just yet.

So those are the issues that Benz found. I have been looking around but haven't found a place where I can get a replacement PSE unit. Anyone have any ideas? Would this be something that a non-Benz dealer mechanic could order and install?

Thanks everyone for your thoughts!!

-L
 

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A PSE is not terribly difficult to replace, there is quite a bit of information regarding its problems and replacement on this forum. You can order the part for $464.00 (Dealer retail $580) from these guys: mbwholesalepartsonline.com I have used them for new parts with good results.
I could probably replace one in 2-3 hours, and I am far from a professional mechanic. Most of the time is spent taking out panels and stuff from the trunk. Most independents that work on Mercedes, etc. could handle the job easily for $200-300 dollars.
 

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Discussion Starter #13
Thanks CarolinaBluetec! It appears mbwholesalepartsonline.com refers to the PSE pump just as a "vacuum pump". But I assume this is the right part. The pricing and location match. Their return policy is a bit harsh though -- maybe that's just normal in the industry?

I think most Benz mechanics can handle the motor mount for me so I will be having that done after calling around to a few places.

The good news is the dash circuit board is okay. I picked up the car yesterday and talked to the mechanic. He said he cleaned it up and got it working fine. The only issue is that it's an older car and eventually the board will need to be replaced. To be expected.

The best news is that the engine is in excellent condition and, with the tune-up, it purrrrrs again. :)
 
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