Wednesday, June 8, 2011

Trunk lid not closing fully on Mercedes Benz car?

If I manually apply pressure to the mechanism it will pull the latch to the fully closed position (off the car).

Likewise, pressure to the tube that feeds the release solenoid will un-latch it.

This systems are operated by air pressure.The pressure runs from the pump to close and pressure lowers when you click to open the trunk.If the pressure is loosing from the pump or the pump hose is cracked the trunk lid will not close.--------- In most of the cases the pump needs to be replaced.
The problem can't be in the trunk lid unless a micro-switch is messing up.


When I press the unlock button the electrically activated pneumatic valve clicks to route the pressure to the unlock solenoid, but it does not REMAIN engaged, and the pump does not engage to create pressure to activate the solenoid. If I apply a little pressure to the inlet and press the button, there is a little bit of movement in the solenoid when the electric valve engages, but because it disengages almost immediately, there is no unlocking action other than a little wiggle...


Why does the electric solenoid disengage so quickly?
Why does the pump not engage and make a little pneumatic pressure?



When the latch is clicked to the first closed position, the pump engages, and there is some pressure felt at the pneumatic tube to the solenoid, but it is very weak compared to what is needed to activate closure. The pump runs for several seconds and stops, presumably with a timeout. In a couple of seconds the pump engages a second time for a couple of seconds with a different sound.


Why is there not enough pressure generated from the running pump to activate the closure solenoid?

If I cover the tube from the pump with my finger and activate the closure cycle, the pump runs for the same amount of time. In theory, I'm thinking if it sensed the pressure had reached the specifications, the pump would have disengaged earlier...

In the closure scenario, I'm thinking there is either a leak in a hose that prevents the pump from reaching full pressure, or something in the pump is not creating the pressure in the first place.

The connectors at the pump are labeled. The one to the trunk latch is labeled "HECK". If I disconnect it at the pump and apply a little pressure to the tube with my air gun, it will READILY operate the close assist.

I'm thinking the pump has a problem... It DOES engage to close the trunk. It will hiss if the tube is disconnected while the pump in engaged, but doesn't seem to create enough pressure to operate the closure.


If it never pulls down the lower latch could have loosened, which is a simple fix, remove the liner and adjust the screws.

You can try and rotate the lower latch to see if the catch retracts, otherwise it is a bad latch but probably a failing pump. The pump is expensive $600 plus and located over the driver rear wheel way back in there (remove liner).

One users review, read it.-----------

the bottom latch assembly was nice and tight. I found the latch on the trunk lid itself was loose, so I loosened the two screws and adjusted the position of the assembly then retightened. I think I have the latch as well aligned as possible. still the trunk does not close fully.

tested the yellow airline to the lock mechanism (supplied to the left side) and it works. there is an air powered actuator to the right side of the lock mechanism which looks like it springs the latch on the trunk when it operates. I can not get this to work

which air supply actually operates the trunk lid closing function? i think this is where the leak is bc i do not hear the normal low pitched whining noise of a vacuum powered mechanism operating when i close the trunk. When i close any other door and the autoclosing is utilized, i hear this noise as the vacuum closes the door. then about 10 seconds later I hear a puff of air in the trunk on the driver side. oddly enough this puff noise does not happen when i close the trunk! seems to be coming from a metal tube that runs toward the rear of the car near the antenna mast and motor. is the puff of air a normal sound like bleeding excess pressure from the vacuum pump? or is that the sound of leak?

Answers to this review is faulty pump.

I pulled fuse number 9 and 10 , waited 20 seconds, put it back in and the trunk closed completely.Removing and reinserting fuse resetted the trunk circuit.


if you examine the air lines connected to the lock catch in the body of the car, there are two of them. one connects to the left side, and seems to actually lock/unlock the trunk. the second supplies a pneumatic ram on the right side of the lock assembly. this ram connects to a spring and a hammer, the hammer strikes a release mechanism on the lock which springs the catch - presumably to spring the trunk open under some command.


In some rare cases its not the pump or fuse issue but its faulty switch .Please read this article below and get more help:----

Getting to know your Closing Assist Pump: Function, Tips, and Fixes


If you’re reading this, you must be having problems with your closing assist system. Probably it doesn’t work at all. You may have experienced the slow door by door failure that many seem to report. One door stops working. Or trunk not closing fully. Then over the course of a week or so, all the doors and the trunk stop working one by one until eventually nothing works. Before you go for new pump (about $400 right now), allow me to see if I can convince you otherwise.

knowing that the closing assist system was not functioning . This procedures got me started in the right direction, but I learned more than I expected as I dug into the problems with my system. I’ve been able to breathe new life into my pump and return my system to 100% reliable operation for almost a year so far. This document compiles my expertise gained from troubleshooting my own system and from helping a couple others on the board do the same over the last few months.

There are two air pumps onboard your W140, the pneumatic system equipment (PSE) pump (also referred to as the central locking pump) and the closing assist pump. The PSE pump performs several functions including locking/unlocking of doors, inflation of lumbar support bladders, operation of reverse antennae on the earlier cars, extension and retraction of the trunk handle, release of the trunk striker eye for auto-closing, and providing vacuum to the vacuum reservoir when the car is not running. This pump is located under the rear seat on the passenger side. The closing assist pump is involved only with the auto-close function of the doors and trunk lid. It is located in the trunk.

II. Accessing the Closing Assist Pump

The closing assist pump is simply crammed into a foam cube tucked between the left rear fender well and the gas tank. You must remove the trunk liner on the left side, and it helps a lot to remove the liner piece at the forward wall of the trunk. It is possible to just bend the corner down to get the pump out, but access is much easier if you remove the whole liner. It only takes removal of a few more of the plastic push rivets. If you have a CD player, you must remove this first in order to remove the left side liner. It’s easy: 2 screws and one electrical connector. If you don’t see the pump at first, follow the bundle of red plastic air lines.

Just pull the pump out. The lines are labeled with initials which, I believe, are short for German. VR = vor rechts = front right door. HR = hinter rechts = rear right door. VL = vor links = front left door. HL = hinter links = rear left door. HD = not sure = trunk. SK = not sure of this one either = pump outlet line, hooked up to nothing.

I understand that for coupe models, the pump is identical, but the rear door lines are simply not used. One boarder (jvallet) stated that it should be possible to use the rear door outputs if one of your front door lines becomes unusable by simply plugging the appropriate door line into the rear door output and then rewiring the connector so the micro switch sends the proper signal to the pump to activate the rear door output. I cannot comment further.

III. Pump Function

Understanding how the pump functions is central to identifying any problems with your system. The heart of the pump is a sizeable electric motor that directly drives the air pump. What is neat about the design is that the pump can both pull a vacuum or develop pressure on any of the door or trunk lines independently and at the same time. That way only the door or doors that need it get pulled closed. This is accomplished by electric solenoids that switch each line between pressure and vacuum. The solenoids are controlled by the pump electronics which receive signals from micro switches in the door latches and trunk latch telling the pump that a door has partially closed and needs to be pulled shut.

The pump does the closing of the doors and trunk with pressure. It pressurizes the lines causing the extension of pistons in actuators, which in turn move levers in the various latches, which pull the doors or trunk closed. The pump runs until one of two things happens: 1. It reaches a pre-set shut-off pressure (at which point the pump "thinks" it has properly done its job of closing the door or trunk), or 2. It never reaches its pre-set shut-off pressure and then runs for a set amount of time and turns off (that is, it "times out"). After pressurizing the line and doing the auto-closing, the pump then pulls a vacuum on the line, presumably to ensure retraction of the actuator piston. The pistons are spring loaded, but I suppose occasionally, they may not retract fully when the pump releases pressure.

Case 2 is where a lot of problems arise. If the pump times out twice on the same door or trunk line, the pump electronics permanently turn off function for that line. That’s just the way the system is programmed, and it’s usually why just one door stops working. The pump specifically turned off that line because it timed out twice. Back to why the pump timed out… because it couldn’t reach the pre-set shut-off pressure. Why couldn’t it reach its pre-set shut-off pressure? Two reasons: 1. Because an air leak has prevented build up of enough pressure or 2. Because the shut-off pressure is set too high. So the course of action is clear. If you don’t have an obvious air leak, you’ll want to address the shut-off pressure. The pump has a pressure sensing shut-off switch which is adjustable. The following troubleshooting section will show you how to reduce the shut-off pressure on your pump thereby preventing the pump from timing out and shutting down on its own.

This very simple adjustment completely restored reliable function to my system. Hopefully, it can for yours, too, but there are many other failure possibilities, which I’ll discuss in the next section.

IV. Troubleshooting Your System

Note: Be careful when removing the air lines from the pump. I used a screwdriver to pry them off and had no problems, but I know that others have broken off the nozzles, which may force you to buy a new pump. Make sure you pry against the hose end, and not the barb on the outlet. I have found the factory recommended method is to use the fork of a 7 mm wrench as a pry tool so that you get prying force distributed equally on either side of the air line connector. Note that the 7mm wrench trick is for the "male" style hose ends. Also - the contactor on the newer style pumps doesn't shut the pump down immediately on contact. There's a delay before the pump shuts down. Keep this in mind when testing.

a. Bringing Your Pump Back to Life

There are two reasons why a door may fail to close. Either your pump is not working, or your pump is not getting a signal telling it that a door has partially closed, i.e. the micro-switch is bad or out of adjustment, or the wiring from the switch to the pump is bad. Most likely, it’s the pump that has shut down. First thing to do is to try pulling fuse 9 in the trunk fuse box. Pull it out, wait several seconds and replace it. This fuse is labeled for the closing assist pump. Try a door or the trunk to see if the pump turns on. Some have reported this works to bring their pumps back to life, but this never worked for me. At this point, pull out the pump as shown above, and remove the electrical connector on the pump, and replace it. Completely cutting power to the pump resets the electronics so that it will again operate all lines until the two-time-out thing starts happening again. If you do nothing else, your pump may work for a while, but it will again eventually shut down because of the same reasons that caused it to time out in the first place.

If your pump comes back to life, congratulations. You very likely don’t need a new pump. If it doesn’t, I probably can’t help you. Perhaps the electric motor has shorted out. It works hard and gets hot very fast inside the pump housing. Or maybe the brushes have simply worn out. It may be possible to replace the brushes, but I don’t know. If you’re electronically inclined, maybe you can tackle the problem. There is also a printed circuit board inside the pump. Plenty of components can fail there, but I cannot address this.

If you have a door that works intermittently (sometimes a door works and sometimes it doesn’t, seemingly at random), your problem may be a micro switch issue. Sometimes the micro switch gets tripped and sometimes it doesn’t when you close the door. Intermittent function is never a pump issue. Once the pump shuts down a line, it’s off for good (until you completely electrically disconnect it by pulling the connector).

Once you have the pump on your trunk floor, you can observe the two-time-out-then-shut-down behavior of the pump. Disconnect the trunk line (HD), and leave the nozzle open. Now, simulate the closing of the trunk by operating the catch in the lower trunk latch with your thumb. The trunk lights will turn off, the trunk handle will retract, and the HD line will hiss loudly with air pressure from the pump. The pump will run for around 10 seconds and then stop. All seems well. Do it again. All seems well. Do it a third time, and nothing will happen with the pump any longer. Unplug the electrical connector and plug it back in. Simulate trunk closing again. All back to normal.

Now, check your pressure shut-off mechanism. Put your thumb firmly over the HD nozzle preventing any leaking, and then simulate trunk closing. The pump will start up, and it should shut off almost immediately. That is because it pressurized the trunk line, and with your thumb over the nozzle, it reached the shut-off pressure very quickly and turned off. You can repeat this indefinitely. As long as the pump reaches its shut-off pressure and doesn’t time out, it operates just fine. If your pump doesn’t shut off when you do this, you’ve got a more serious problem with the pressure shut-off switch.

b. OK, My pump works. Now what?

Leak checking is next. As mentioned earlier, air leaks will cause the pump to time out because a leak may prevent reaching the shut-off pressure. There are a couple of ways to find leaks. You can use a pressure device with a gauge (Mity-Vac or similar) to pressurize the line in question and watch for leak down. There are specific Mercedes factory specs for leak down. I don’t know what they are, but it is on alldata. Alternatively, you can simply operate the door or trunk once you’ve reactivated the pump and listen carefully for the telltale hiss of a leak. The pump really moves a lot of air. I believe that any leak large enough to prevent the pump from reaching the shut-off pressure will be audible. Just listen.

There are myriad opportunities for leaks. Lines can separate inexplicably from connectors. Lines can get pinched and crack. Lines can get chaffed and worn through. The actuators are also a source of leaks. These have rubber o-ring seals that can get hard and crack with age. There may also be leaks internally inside the pump. These may be fixable or maybe not. More on this later.

One boarder (beelootin) contacted me recently when his trunk stopped working followed by everything else. After he found his pump was fine, his mechanic turned down his pump’s shut-off pressure per my instructions and also found the trunk line had a leak in it. Apparently the line was routed poorly and was rubbing somewhere every time the trunk opened and closed. They cut out the holed bit of line, rejoined it with a good seal, and his system is now working fine.

c. I’ve rejuvenated my pump by electrically disconnecting then reconnecting it, and I’ve confirmed that there are no major leaks. Now what?

It’s time to evaluate your pump’s pre-set shut-off pressure. You can use any door or the trunk. Partially close the door/trunk, and carefully watch the closing action. You’ll hear an audible click when the latch catches, but then the door/trunk will be pulled shut for a period of time after the click of the latch. Finally, the pump will turn off and the door/trunk will relax to its normal fully closed position. First, time how long it takes for the door to audibly latch. This should be about 1-1.5 seconds. If it takes longer to latch the door, your pump is not providing enough pressure. Why? Leaks, or maybe a worn out pump head, or something else (??). If you can’t find a leak, then I probably can’t help you further.

Now, time how long the pump runs after the door or trunk has audibly latched (that is, how long it keeps the door “sucked” closed after it latches). I found my pump ran for almost 10 seconds after the latch had clicked, needing extra time to build up enough pressure to trip the automatic shut-off. This extra pumping time is unnecessary. If your pump takes more than 7-8 seconds to shut off, then you’re a candidate for adjusting the shut-off pressure.

The pump only needs to run as long as it takes to latch the door. The risk of your pump running for too long is that every once in a while, before it reaches its shut-off pressure, it instead reaches the time-out time and charges a time-out to that line. After one more of these, that line is dead. The pressure shut-off is a balancing act. You want to set the shut-off pressure high enough so that enough pressure is developed to latch the door or trunk, but you don't want it set too high so that the pump takes too long to reach the set pressure and times out.

d. Adjusting the shut-off pressure

Pull out the pump and disconnect all the lines. Label them before disconnection if they aren't already. Unscrew 6 screws on the top of the pump, and pry off the cover.

Admire the dual manifold design with solenoid switching between pressure and vacuum for each door and trunk line. Kinda cool. The pressure shut-off diaphragm is visible in this pic.

OK, here's the business end. Notice the dual contact switch that is operated by the white piston from the pressure sensing diaphragm. That white piston has a screw in the end of it which can be adjusted to adjust the shut-off pressure. If you screw it out a bit, then the piston will have to move less to trip the switch; therefore, the pump will shut off at a lower threshold pressure.

Just turn the screw to adjust it. I just used needle nosed pliers. Finally, here's my original vs. new setting.

Now, your pump will shut down automatically in a lot less time after closing the doors and trunk. You can play with the adjustment a bit so that the pump run time is to your liking. I’d say 3-4 seconds after the latch closes is all that is needed, and you could probably set it for less than that. My closing assist system has run with 100% reliability for almost a year now, after performing the shut-off pressure adjustment. The obvious fringe benefit of this adjustment is that the pump runs for a much shorter time each time it closes a door, so it should also extend the life of the pump’s motor.

e. A case of a bad pressure shut-off diaphragm

This finding convinced me that most closing-assist system failures that W140 owners experience may well be caused by either maladjustment or failure of the pressure shut-off mechanism.

A boarder posted that his pump had quit running. I responded insisting that he adjust his shut-off pressure. When he dug into his pump, he found that the problem was not that the shut-off pressure was set too high, but that the white piston of the shut-off switch mechanism wasn’t moving at all. So his pump was timing out every time it operated. The piston had cocked to one side and bound in the black case becoming stuck (see pics above). He went farther than I ever had and disassembled the diaphragm (the black housing that the white piston moves in) eventually finding the root cause of the sticking piston. It turned out that the rubber diaphragm that pushes the white piston had developed a tear. The tear was on one side of the diaphragm such that as the pump pressurized, the diaphragm would push one side of the piston only causing the piston to cock sideways in the black housing. Since the pump develops quite a bit of pressure, the piston would get wedged in place tightly once it got started crookedly and become permanently stuck. He was able to take apart the diaphragm assembly and use the tip of a latex glove finger to re-seal the diaphragm and make it air tight again. Very ingenious, indeed. He said everything was back to normal, and he had also adjusted his shut-off pressure appropriately in the process.

Here’s a pic showing the 3 screws (green) and the 3 solder connections (cyan) that need to be removed to take the pressure shut-off diaphragm off the circuit board for disassembly.

f. The newer pumps with a different shut-off mechanism design and a technique for fixing leaks from damaged nozzles.

Another boarder (jvallet) posted that his S500 coupe was having driver’s door problems once again after pump replacement for the same problem 3 years ago. Jvallet found the door would work for a very short period, then stop permanently until he disconnected his battery. Then it would work again for a short time. Disconnecting the battery was serving the same purpose as removing the connector from the pump. When he pulled out his newer style pump and listened while it operated the driver’s door, there was an obvious hissing sound from a leak. He wiggled the air line connector on the output nozzle and found the noise changed. He found he could adjust the connector and minimize the leak enough to get the door to close, but the pump would run for 7-8 seconds before it reached the shut-off pressure. Although the leak was reduced, it was still audible. When he removed the air line, he found that the nozzle had a small chip broken out of it that appeared to be causing the leak. Jvallet wrapped the nozzle in what he described as water pipe sealant (I think Teflon tape) and then replaced the air line connector. When he tried the driver’s door again, it operated just fine, and the pump shut off automatically in about 2 seconds after the door latched. Problem solved. There were no more sounds of a leak.

Jvallet kindly provided this pic of the newer style pump. I have circled the output nozzles with chips in them. He reported the nozzles were particularly fragile, and he actually caused one of the chips when he was placing the cover back on the pump. On the right of the pump is the new design of the pressure shut-off mechanism. There is still a screw to adjust the shut-off pressure, but in this case, the screw is the actual electrical contact that turns the pump off.

g. Severe air leaks from loose bolts at the pump head.

A poster (SEXYREX) recently related his experiences with fixing a major leak inside his pump. Every time he reset the pump by pulling the fuse, he would get two operations then nothing from each line. Even firmly blocking an output line with a finger, did not cause the build up of enough pressure to trip the shut-off switch. Clearly, there was a major leak central to the pump since every line was affected equally, or there was a problem with the pressure shut-off switch causing timing out. After some inspection, he noticed dust patterns indicating air escaping from the seam in the pump head. It turned out that the screws holding the pump head together were loose. A quick tightening of the screws completely restored function. Now, when firmly blocking an outlet nozzle, the pressure shut-off switch turns the pump off immediately as it should. After adjusting the shut-off pressure, all doors operate normally, and the pump turns off about 3 seconds after latching.

(1995 pump shown)

h. A case of a plugged line to the pressure shut-off switch diaphragm in the newer style pump.

A boarder (GotBenz) posted that he was experiencing the typical loss of function of the doors and trunk one at a time in rapid succession. The fact that all the lines were affected is indicative of a problem central to the pump rather than a leak in a single line. He found he had the new style pump in his W140. When he tried to turn the copper screw of the shut-off switch mechanism, it seemed really stiff and resisted adjustment. (I only know this pump from a picture. I’ve assumed that the screw is a pressure shut-off adjustment, but if it is fixed, then the shut-off pressure may not be adjustable. I’ll update my info when I learn more about the shut-off mechanism of the new style pump.) GotBenz then attempted to adjust the shut-off pressure by shortening the distance between the switch contacts by dabbing solder on the moving copper arm of the switch. It didn’t work reliably. I suggested that he take a close look at the shut-off mechanism while in operation, and he found that the copper arm of the shut-off switch was barely moving. Further investigation revealed the culprit. The pump head is made of a black material that produces a fine powder as it wears. It may be graphite or just a plastic. This powder had plugged the line going to the pressure shut-off diaphragm, so the switch wasn’t operating properly. GotBenz simply removed the plugged plastic part and blew backwards through the line ejecting the powder. Upon reassembly, the shut-off switch was back to normal operation, and pump operation was completely restored. In his own words, “so.. with a swift blow through one of the air inputs, a large, rather hideous cloud of "black smoke" came spewing out the other nozzle. Be careful and point the air nozzle away from face when doing this.. or suffer the consequences like I did...ha ha...anyways, reassemble air hose, and problem fixed!” The pic below points out the part where the blockage had occurred.

A picture of a "healthy" vane mechanism in a 1995 model...

A picture of a broken vanes...obviously this pump isn't working .

The material that these items are made of creates a fine dust over time. This dust can accumulate and pack into the spaces of the moving parts or hoses. It must be cleaned out. NOTE! Do NOT lubricate these components with any oils or greases. Lubrication will simply trap the dust and make things worse. These parts are meant to run dry.

i. A weak battery causes a weak pump and timing out. I recently got a message from Simon in Australia describing his experience with his closing assist pump. He had the car for two months, and his pump was regularly shutting down. Pulling fuse 9 in the trunk worked to reset the pump, but it was required every couple of days. Then his battery died. Testing the battery confirmed that the voltage output was very low. It turns out that replacement of the battery seems to have restored good function to the pump. No more timing out. While you wouldn't experience this "failure mode" for any length of time since you'll be forced to replace your battery, it is interesting information nonetheless. A timing out pump could be a sign of a weak battery.

New Sections j and k...

j. Making an access cut-out in the pump housing. Bob B. contacted me with an interesting modification that he made to his pump. After removing the pump’s cover to make the shut-off pressure adjustment to his Bosch pump, he actually cut a flap in the side of the pump cover right where the shut-off switch is located. Now future adjustments can be made without needing to disconnect all the air lines. Not a bad idea. And by the way, reducing the shut-off pressure has completely restored operation to his closing assist system. Here’s a picture of his handiwork. Note that this may be practical only for the Bosch closing assist pump. I’m not as familiar with the Hella pump.

k. Another failure mode of the Bosch pressure shut-off switch. Guide fins breaking off of the white plunger. Thanks to Simon C. for describing another failure of the Bosch pressure switch. Simon’s pump was timing out regularly. Upon closely watching the white plunger of the shut-off switch, he noticed (like did in section e) that the plunger wasn’t moving at all. He tried pulling the plunger with needle-nose pliers, but it still would not move, so he resorted to disassembling the pressure shut-off diaphragm. The culprit turned out to be broken fins on the white plunger. The plunger has several tiny fins around its perimeter, which guide the plunger by mating to slots in the black housing. A couple of these fins had broken off and jammed the plunger. In his case, the rubber diaphragm inside the cylinder was fine. Simon simply removed the plunger and cleaned out the debris. Upon reassembly and adjustment of the shut-off pressure, his pump was back to normal operation. As he describes, the shut-off switch diaphragm can be separated into two parts and repaired without de-soldering the electrical part of the switch from the circuit board. First, remove only one screw holding the rear section of the black plastic housing to the circuit board.

Second, release all the small clips around the circumference of the black housing to separate the rear of the diaphragm, leaving the section encasing the white plunger connected to the circuit board. You can now remove the white plunger and the rubber diaphragm to inspect them for damage.

Update 12/27/07

Installing an aftermarket pressure shut-off switch in the closing assist pump

l. Installing an aftermarket pressure shut-off switch in the closing assist pump. Here is one of the most ambitious repairs to the closing assist pump that I have had the pleasure of documenting. I corresponded recently with user who successfully installed an aftermarket pressure shut-off switch in his closing assist pump.

He found a switch from, part number 6101-0018, manufactured by Herga.

This switch operates at pressures from 0.025-2.75 bar (1-40 psi). There are 4 different springs that come with the switch so that you can choose the correct operating pressure for your application. The closing assist pump is supposed to reach pressures greater than 2 bar during normal operation, and he reports the proper spring to use is the one in the yellow bag labeled 13-0022-A-87.

The installation is pretty simple according to pics. Here is a close-up pic of the new switch showing the contacts that are used.

First, you must desolder the old pressure shut-off switch from the circuit board, and disconnect the air line to the switch. See pic in section e. There are only two actual electrical connections, but there are three solder connections. The third solder connection doesn’t connect to anything electrically. I guess it’s there to help hold the switch to the board.

Now, solder two wires that will go to the new switch to the electrical contacts on the board.

Solder the two wires to the switch contacts shown, and using about 10 mm or less of a flexible plastic hose with 4 mm ID, connect the new switch to the air manifold.

Before you put the pump back together, you need to adjust the pressure shut-off properly. So, using the trunk or any door, do a test closing run, and time the operation of the pump as described earlier. There is a screw on the switch to adjust the shut-off pressure. Adjust the switch until the pump run time after the door or trunk has latched is about 2-3 seconds.

That’s it. The rest of the job is packaging the switch properly in the area where the original switch resided. Be careful not to pinch or kink the air line. In the two following pics, you can see that used wire ties to hold the switch in place and secure the air hose.


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