When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have the usual problem of the trunk self close causing the PSE pump to shut down requiring a power cycle to reset it. In my case, the self close works but the pump runs on and eventually times out.
I know there’s a sticky which majors on sealing leaks but I have pressure tested mine and it’s fine. My question is once the pump has been started to do the soft close, what should cause it to stop running?
The three pin connector in the latch is to two microswitches which are set depending on the position of the latch - open, partially closed, fully closed. Connecting a wire between pin 1 (brown) and pin 2 (brown/green) simulates the trunk being open. The trunk interior light comes on. Removing that link simulates the trunk lid being closed to a first click and the PSE pump starts and the latch moves to fully closed.
Common sense tells you the PSE motor should stop when the fully closed position is detected. However, these switches are not connected to the PSE pump but to the rear SAM and the only way the PSE pump will know is by repeatedly asking the SAM “is it closed?” or else if the SAM tells it “it’s now closed” using CAN bus messages.
A diagnostic iCarSoft box correctly reports the state of the switches, so the rear SAM knows about the switches but for some reason the PSE pump does not know to shut down and times out. While doing so, the pressure in the line is something like 40 PSI.
Since all other PSE functions are working normally (central locking etc) it seems CAN bus communication to the PSE is fine, so why isn’t it shutting down when the SAM knows the trunk is fully closed?
I know a replacement PSE has to be personalised to the car using STAR and I’m wondering whether my PSE pump need re-personalising?
I have the usual problem of the trunk self close causing the PSE pump to shut down requiring a power cycle to reset it. In my case, the self close works but the pump runs on and eventually times out.
I know there’s a sticky which majors on sealing leaks but I have pressure tested mine and it’s fine. My question is once the pump has been started to do the soft close, what should cause it to stop running?
The three pin connector in the latch is to two microswitches which are set depending on the position of the latch - open, partially closed, fully closed. Connecting a wire between pin 1 (brown) and pin 2 (brown/green) simulates the trunk being open. The trunk interior light comes on. Removing that link simulates the trunk lid being closed to a first click and the PSE pump starts and the latch moves to fully closed.
Common sense tells you the PSE motor should stop when the fully closed position is detected. However, these switches are not connected to the PSE pump but to the rear SAM and the only way the PSE pump will know is by repeatedly asking the SAM “is it closed?” or else if the SAM tells it “it’s now closed” using CAN bus messages.
A diagnostic iCarSoft box correctly reports the state of the switches, so the rear SAM knows about the switches but for some reason the PSE pump does not know to shut down and times out. While doing so, the pressure in the line is something like 40 PSI.
Since all other PSE functions are working normally (central locking etc) it seems CAN bus communication to the PSE is fine, so why isn’t it shutting down when the SAM knows the trunk is fully closed?
I know a replacement PSE has to be personalised to the car using STAR and I’m wondering whether my PSE pump need re-personalising?
Any ideas anyone?
Did you solve your PSE pump problem? I have exactly the same situation. I have even removed the air controller from the air line (replacing it with a sample hose between the two lines) and still the PSE pump won't shut down for about 13 seconds. I get two cycles then the 20A fuse has to be pulled and reinserted. To complicate matters more originally the pump was shutting down as it is supposed to do but has now decided not to shut down until the 13 sec time. This happened during the time I was replacing the hydraulic trunk cylinder for the vario roof. The PSE pump pressure is strong. I've decided for now I'm not going to go into the PSE Pump for something I can take care of in 30 seconds by pulling the fuse. Still I'd like to know how to fix the problem. I read about one person putting a timer relay in the line to automatically interrupt the circuit but no details were given other than he did make it work until his controller leaked so badly he had to stop and fix it.
Hope to hear from you.
I found this link. There is a ton of detail information here about the pump including how to fix it. According to this link if the pump task isn't completed in 5 seconds and takes 10-16 seconds then there is a problem with the pump. There is enough psi created to do the required trunk soft close almost instantly even if the pump doesn't think it is doing its job. I have other repairs I want to make to the car but I'll read the reference material to see what is involved in rebuilding the pump since that seems to me what this reference is telling me. I would be interested in what you think after looking at this link.
Did you pressure test the line between the pump and the trunk actuator for leaks?
Yes, I pressure tested the line to the actuators with a MityVac and everything was fine, for both the unlock actuator and the self-close actuator, including energising the diverter valve to switch from one to the the other. You were right to ask though. Clearly the PSE pump can only do its job if there aren’t any leaks.
I found this link. There is a ton of detail information here about the pump including how to fix it. According to this link if the pump task isn't completed in 5 seconds and takes 10-16 seconds then there is a problem with the pump. There is enough psi created to do the required trunk soft close almost instantly even if the pump doesn't think it is doing its job. I have other repairs I want to make to the car but I'll read the reference material to see what is involved in rebuilding the pump since that seems to me what this reference is telling me. I would be interested in what you think after looking at this link.
I found out that the trunk self-close is not closed loop - the pump does not monitor whether the trunk is latched closed. It simply opens the valve to the actuator, the pressure drops, the pump starts and continues until the pressure returns to normal, the pump stops.
why the pump was taking so long, I never found out. First I bought a scrap PSE - basically the electronics without the pump and swapped over the pressure sensors, the one with a leaf spring and the one with three wires which looks like a small battery. No change in behaviour.
At this point, I was in contact with David Arnott here in the UK who sold me a pump on exchange and installing it fixed the problem instantly and it’s been fine ever since. I asked him to tell me what was wrong with the old pump and he was rather vague, fair enough, he’s invested time in understanding and fixing these things. His exchange price was about 40% of the price quoted for the part alone by Mercedes.
My pump first failed after the car had spent the winter with the pump inside the foam surround which was wet.there was no sign of water ingress into the pump but it certainly was not working in the dry environment intended. It really is important to check that water is not leaking into the trunk through the roof.
So, I saved some money compared to having Mercedes swap out the pump and program it. The exchange pump doesn’t have a warranty and I spent money on the MityVac and the scrap pump trying to fix it myself.
I am a few days behind you. Thanks for your posts. Glad you are back up and running.
I've worked on the lock assembly per the other major soft close thread, epoxied the bearing holes, etc. but with no improvement. Mine does exactly the same as yours, right down to the 13 second delay before the red light comes on. Of course, reset of # 71 is needed to soft close again, and I suspect the top is inoperative with that red light on.
However, I am trying to understand why, if the PSE pump is being shut down, does only the trunk latch air leg shut down but not the other legs? It would seem the leg is the problem and not the PSE pump. Since you are way ahead of me on this, can you see what I missed as I am not at all familiar with the circuitry for the PSE pump. I wondered if what you might be telling us is that the PSE pump is worn, not producing enough air before timeout. But even so, I'd think other applications of the PSE pump should have the same effect.
I don't have a David Arnott here, so I'd really like to understand the root cause here before going to the MB dealer's shop (wince $$, wince $$) and replacing the PSE pump if that is not the root cause. Hope you can help. Thanks.
I am a few days behind you. Thanks for your posts. Glad you are back up and running.
I've worked on the lock assembly per the other major soft close thread, epoxied the bearing holes, etc. but with no improvement. Mine does exactly the same as yours, right down to the 13 second delay before the red light comes on. Of course, reset of # 71 is needed to soft close again, and I suspect the top is inoperative with that red light on.
However, I am trying to understand why, if the PSE pump is being shut down, does only the trunk latch air leg shut down but not the other legs? It would seem the leg is the problem and not the PSE pump. Since you are way ahead of me on this, can you see what I missed as I am not at all familiar with the circuitry for the PSE pump. I wondered if what you might be telling us is that the PSE pump is worn, not producing enough air before timeout. But even so, I'd think other applications of the PSE pump should have the same effect.
I don't have a David Arnott here, so I'd really like to understand the root cause here before going to the MB dealer's shop (wince $$, wince $$) and replacing the PSE pump if that is not the root cause. Hope you can help. Thanks.
If the fuse is reset, the soft close will work and the roof can be closed. I just finished replacing the trunk hydraulic cylinder so I know it works. The soft close worked as it should before I started to work on the cylinder. Maybe I got hydraulic fluid in there somehow. I'd like to understand why the pump runs for 13 sec and how it should be fixed. Also what happens if I don't fix it right away. I tied a cable tie around the fuse so I can disconnect it quickly. Another point- I could not figure why the PSE ran all the time when I opened either door. I turned the seat bolster dials down to 0 on both seats. Problem solved. I need to replace the hydraulic cylinder for the roll bar before fixing the PSE Pump but still want to know how to fix it so hopefully something will come up. I found a person in the UK who will help diagnose the PSE problem for a fee. I'm waiting to hear back from him.
As we’re finding, not every soft close failure is down to a leaky latch mechanism and for others coming here to this problem, the first thing to do is to test the latch before breaking out the epoxy and hoping for the best. You will need a hand pump (MityVac) and a 12v battery and pin connectors to activate the diverter built into the latch which supplies air to one or other of the actuators build into the latch.
You disconnect the single airline from the port marked “Heck” (German for “rear”) and attach it to the MityVac using the various adapters which come with it. You should be able to pressurise the line and not have it lose pressure (as indicated by the MityVac meter). You should also be able to operate both actuators using the MityVac and diverter. The car should also respond to the different latch positions (fully open, partially closed, fully closed) with things like the trunk light, the red light on the door switch. If you can do all of that, the latch is fine and you can put the epoxy away.
The PSE creates both pressure and vacuum in the plastic manifold and depending on the function needed will connect the pressure or vacuum to the line. Normally, when you lock a door, the pump runs for a short time to top up the pressure/vacuum and then stops. The big question is why it doesn’t stop on after a trunk soft close but runs on until the control processor times it out to prevent the pump overheating. The pump consumes a lot of power and gets very hot very quickly if not timed out in this way.
The PSE logs information and errors and in this fault condition, the errors are clear to see but there is no explanation as to what is causing it. I believe it’s because the pump is not generating enough pressure to get the PSE back to ready state.
I’m afraid this is where I drew a line and bought an exchange pump. I’d spent too much time trying to figure out what was wrong!
To answer bill’sMB‘s question, when the PSE pump performs a soft-close of the boot / trunk, it attempts to pressure the line to 2.7 bar (39 psi) and hold this for several seconds. If this pressure is not reached or drops off for several attempts then the PSE disables the soft-close function and sets a fault code. (The safety time of the power closing has been exceeded for the following pneumatic branch: Trunk lid )
The PSE is reset by interruption of the 12v supply, and the sequence of pressure tests is restarted.
There can be two causes that the 2.7 bar cannot be reached, either a leak or insufficient pressure developed by the pump in the PSE. A correctly functioning pump will develop at least 50 psi when connected directly to a gauge.
The PSE does a similar thing on some of the other pneumatic outputs, for example the pressure supply to the seats.
David, thank you for your answer to my question about the operation of the PSE Pump. I'll check the line pressure developed by my pump. I know it is currently much higher than required to operate the latch. I have other work I'd like to do on the car right now as long as the pump keeps running.
Sounds like a lot of work to replace, or rebuild the PSE pump especially since I just finished working in that area of the car replacing the trunk hydraulic cylinder. I'm inclined to just use the disconnect, reconnect 20A fuse option. I did find one other option someone used. They connected a timer relay which goes open circuit after around 5 seconds when the control power to the PSE motor activates and then closes again. The relay basically makes the fuse open and close, same as pulling the fuse without pulling the fuse. This modification worked for several years, no other details were given except that a $5 timer was all that was required. If anyone has more information on the use of this design, it would be very helpful to see the details.
The trunk soft close, trunk close, and the PSE pump problems impact thousands of S and SL model cars. I have seen one thread that has over 300 comments over 14 years just on the air controller for the trunk soft close. It is unbelievable that Mercedes could let these fundamental design flaws exist for so long.
I checked my PSE Pump pressure for my soft close trunk application by connecting to the gauge on my tire pump through a few feet of clear hose I had lying around - the pressure went to 40 psi in a few seconds and stayed there for the 13+ seconds and then the pump shut off like it always does. At first I thought that the problem was solved - the pump needs a new rotor but then I read your message again about the 39psi. Given the fact that the pump was shutting down regularly when I first started to work on the retractable roof trunk cylinder replacement, I would still guess that the PSE pump and pump rotor have stopped putting out the pressure required to shut off the pump when it should. It could be clearer but it is what it is. It looks fairly easy to replace the rotor. I can't believe I can buy that rotor from Walmart for $53. Do these rotors all come from the same source? I guess I'll eventually get around to replacing the rotor. My next job was going to be replacing the cylinder on the roll bar as I still have a leak and that one is the only one that hasn't been checked yet.
If you have anything to add to my PSE issue I'd like to hear your thoughts.
Thanks for all the information. The thread Bill referenced on "resetting" had a lot of information helpful in understanding the operation.
bluSL mentioned the pump can get very hot very quickly. This is a rotary pump with a carbon rotor and six carbon vanes, if I remember correctly. The housing is probably aluminum. If so, there is a huge difference in the coefficient of thermal expansion (20 times) which would lead to internal losses as it gets hot. Furthermore, as it wears, the pump can no longer maintain the same seal between rotor and vanes. The conclusion must be that as the pump wears, the output will be decreasing flow/pressure, especially when hot.
Bingo! That would explain why blueSL solved the problem with a new pump, and that he was correct about the pump output probably being less. That does make sense.
So I decided to test the theory with a series of lid closings. The first 7 raise a new question, but the following 9 tests tell me to leave it alone. Anyway, here's what happened:
1.Lid was open for two days for charging the battery. Red light was OFF ??? (should have been on). Closed lid, soft close worked, but red light came ON. (OK)
2.Opened lid, closed, no soft close, red light stayed ON. (OK)
3. Reset fuse #71. Opened and closed lid, soft close worked, but red light stayed ON. (OK)
4.Reset fuse #71. Opened and closed lid, soft close worked, and red light went out. BUT, red light came back ON in 8 - 10 seconds! (??)
5. Reset fuse #71. Same results as test 3. (OK)
6. Reset fuse #71. Same results as test 4. (??)
7. Reset fuse #71. Did not open lid. Red light stayed on, BUT when I came back in an hour, the red light was OFF !!!!!!!! (...wierd.)
8. Opened and closed again, normal results.
9. Next day, repeated test 8, same normal result.
Then, to see if the pump had losses when hot, did 7 tests in quick succession:
10. to 16 All normal.
Yikes; it cured itself! ...not likely. Something is going on in tests 3 to 7 that I do not understand. Maybe you can make some sense out of it. Also, I would have expected the last few in series 10 to 16 to be hot enough to cause low pressure and red light, but perhaps it didn't get hot enough.
Two observations:
1. If this issue is caused by a worn out pump, then having to change the pump before it breaks is a benefit, because when it breaks, carbon pieces contaminate the air line which could cause issues with valves. In a general aviation aircraft where a similar pump is used to power the gyros, that is a big problem, because the pump is operated as a vacuum pump; thus the particles blow right to the lower pressure gyros. Since we have pressure, the debris will likely stay at the pump or upstream. (Clean out the upstream line if you have a failed pump.)
2. If this issue continues, a quick work-around is to replace the fuse with a fuse extender for easy access. I found one at aeswave.com, search p/n 16-202. In the picture the center unit is the one. It is 16-202-ATC for $20 plus shipping. I had to call to order as their site does not show the one separately, but they will sell it that way. I might add a normally-on, push-button switch to eliminate pulling the fuse. I'll get the part in about a week. They tell me it is about 6 " long. Perfect! (Sorry about the attachment size, haven't figured out how to shrink it. Can someone tell me how to shrink this image?)
PSE Rotor and Vane Construction - Graphite
I'll buy that red modified fuse you found. When I first saw it I thought it was a timer.
Why not try the pressure test like I did. You have a cigaret lighter-powered tire pump I'm sure. I have not gotten through your tests yet. I'll look tomorrow.
I'm in Port Saint Lucie.
I hope that your soft-close has fixed itself but my experience tells me that the fix is only temporary.
The problem you had (have?) is that the trunk lid is not completely pulled down, when the lid is closed the pawl on the latch is fully rotated, this is sensed by the switch on the latch and the light on the driver’s door goes off. When the light is still on you will be able to push down on the lid, it will latch and the light will go off. (some people slam the lid)
Again the problem is either a leak or the pump unable to generate enough pressure.
Regarding your “thermal expansion” the housing along with the rotor and vanes are made from graphite.
Regarding the "rotor from Walmart for $53" they come from China, (I see the name X8R as a supplier) a couple of things to note:-
Some of the rotors sold are "handed" the wrong way, they are a mirror-image of the correct item.
If the rotor is not broken, replacing it will not help, low pressure is often caused by a weak motor.
David is correct. Replacing the rotor won't help, except maybe for a very short while.
The wear mode of these pumps is shortening of the vanes as they wear and wearing of the vane slots. As the vanes shorten, the amount of vane in the vane slot diminishes, increasing the bending force causing a vane to break or the rotor to break. Replacing a rotor does not solve the wearing vane issue. It is odd they do not sell a rotor with a set of vanes. Perhaps they couldn't get the chemistry correct. The wear on the housing is probably not an issue for maybe the first replacement.
David is correct. Replacing the rotor won't help, except maybe for a very short while.
The wear mode of these pumps is shortening of the vanes as they wear and wearing of the vane slots. As the vanes shorten, the amount of vane in the vane slot diminishes, increasing the bending force causing a vane to break or the rotor to break. Replacing a rotor does not solve the wearing vane issue. It is odd they do not sell a rotor with a set of vanes. Perhaps they couldn't get the chemistry correct. The wear on the housing is probably not an issue for maybe the first replacement.
The rotors are all sold as a kit complete with the 8 vanes.
I looked on ebay to see exactly what these impellers are made of that the Chinese sellers are offering. The impeller is ABS so unless you have a favorable history you can tell us about using ABS in this application, it is not worth even thinking about using one of these impellers. Do you have a source for replacement graphite impellers and vanes?
In my particular case being the new owner of my 2005 SL500 but knowing the former owner and the car history, my PSE pump motor very well might not be up to the task because the seat bolsters were set to 5 and the bladders were long gone so the PSE pump was likely on as much as it could be for years.
A 20 amp fuse should be used in the application right? I found a 40 amp fuse in the PSE pump fuse location in the car but have switched it out for a 20 amp.
It is interesting that Mercedes has been trying to get this PSE Pump and application sorted out for years. I found a video from 1997 showing customer problems with the pump in S cars.
I took the time to review the rotor suppliers available here. There is a guy in France that looks to me like he is the person I should go with even if he is using ABS. At least he is offering practical technical support. I asked what material his product is made of. One of his customers had a pump with an unbroken rotor that was working but did not put out the 3.5 bar pressure. Changing to the new rotor did bring the pressure up to spec he says. I'll try.
Thanks for your comments. You really gave me direction on what path to take.
04-25-2022, 12:10 AM
