2006 S500 Trunk Won't Open After Hinge + Pump Replacement
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2006 S500 W220 4Matic
2006 S500 Trunk Won't Open After Hinge + Pump Replacement
Title says most of it, but it goes a bit deeper.
The right side hinge had seized on my S500, causing the hydraulic pump to fry itself. I replaced the hinge and the pump. 12V directly on the pump actuates it. Unfortunately, when the keyfob button is pressed, the trunk lid UNLATCHES, BUT THEN RE-LATCHES AND DOES NOT OPEN.
I sent the car to a local euro auto repair shop who claimed to be able to diagnose and repair the issue. After diagnosis, the shop claims the circuitry in the PSE is bad, and the PSE needs to be replaced. I spoke at length to the troubleshooter, who told me he had to "go way back" to remember how this particular system works, which makes me suspect he may not fully remember even now how it actually works, and makes me suspicious of his diagnosis.
He claims he tested the trunk wiring to the relay and it does raise/lower when powered at the relay, but that the PSE seems to be the issue; he says the PSE receives the "open" signal, but fails to trigger the hydraulic pump.
One additional note is that the "SAM REAR FUSE RELAY BOX 0325458432" was replaced a while back due to water submersion (which seemed to bring the car back to working order with no issues).
Any thoughts on this? It seems suspicious to me that that THREE THINGS FAILED at the same time; the hinge, the hydaulic pump, and the PSE. Does the PSE need to be "reset?" MIght the PSE be fine, but not receiving all of the "failsafe" inputs needed to trigger the lifter pump?
I've read through this, but haven't yet found a definitive answer: https://w220.wiki/Pneumatic_System_Equipment_(PSE)
Thanks for reading
-Pete
The right side hinge had seized on my S500, causing the hydraulic pump to fry itself. I replaced the hinge and the pump. 12V directly on the pump actuates it. Unfortunately, when the keyfob button is pressed, the trunk lid UNLATCHES, BUT THEN RE-LATCHES AND DOES NOT OPEN.
I sent the car to a local euro auto repair shop who claimed to be able to diagnose and repair the issue. After diagnosis, the shop claims the circuitry in the PSE is bad, and the PSE needs to be replaced. I spoke at length to the troubleshooter, who told me he had to "go way back" to remember how this particular system works, which makes me suspect he may not fully remember even now how it actually works, and makes me suspicious of his diagnosis.
He claims he tested the trunk wiring to the relay and it does raise/lower when powered at the relay, but that the PSE seems to be the issue; he says the PSE receives the "open" signal, but fails to trigger the hydraulic pump.
One additional note is that the "SAM REAR FUSE RELAY BOX 0325458432" was replaced a while back due to water submersion (which seemed to bring the car back to working order with no issues).
Any thoughts on this? It seems suspicious to me that that THREE THINGS FAILED at the same time; the hinge, the hydaulic pump, and the PSE. Does the PSE need to be "reset?" MIght the PSE be fine, but not receiving all of the "failsafe" inputs needed to trigger the lifter pump?
I've read through this, but haven't yet found a definitive answer: https://w220.wiki/Pneumatic_System_Equipment_(PSE)
Thanks for reading
-Pete
Last edited by Petebacher; Jul 23, 2025 at 10:38 AM.
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Joined: Dec 2012
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From: Ball Ground, GA (N of Atlanta)
2003 S500 2007 GL450
Resetting the PSE control module is trivial. Look in the right rear passenger area and find the floor lamp behind the passenger's heels. Pull the lamp from the carpeted wall, but don't unplug it. Behind the lamp position, find the yellow 20-Amp fuse. Remove it, check it, and if it is good, wait a few seconds, and reinstall it. You have just reset the PSE control module.
The PSE control module in the pump unit must be programmed to match the options installed in your car, especially the hydraulic system.
To open the trunk lid, the control module must see the unlock signal from the keyfob, the trunk handle, or the door switch. (Any difference from any of those?) This signal causes pneumatic actuation of the trunk unlock actuator. When the module receives the "unlock complete" signal from the actuator, it sends the actuation signal to the hydraulic pump.
Some possibilities:
Pump is not correctly programmed.
No "unlock" signal due to faulty switch or broken wire in the trunk lid harness.
No "unlock complete" signal, due to airline off/broken, failed pneumatic actuator,
The PSE control module in the pump unit must be programmed to match the options installed in your car, especially the hydraulic system.
To open the trunk lid, the control module must see the unlock signal from the keyfob, the trunk handle, or the door switch. (Any difference from any of those?) This signal causes pneumatic actuation of the trunk unlock actuator. When the module receives the "unlock complete" signal from the actuator, it sends the actuation signal to the hydraulic pump.
Some possibilities:
Pump is not correctly programmed.
No "unlock" signal due to faulty switch or broken wire in the trunk lid harness.
No "unlock complete" signal, due to airline off/broken, failed pneumatic actuator,
