Odd Noise in the Boot of a 2004 S Class

[DaveG38]

This morning, I went to start my S Class, and I noticed an odd noise from the rear. It is a permanent low rhythmic boom-boom, boom-boom coming from the near side rear. Opening the boot, the noise is coming from underneath the side panel near the back of the rear seat. The noise is there when the engine is running, and when turned off. It only stops when the key is removed from the ignition. Anybody know what is causing this? Car appears to go perfectly well, so no impact on running, as far as I can judge.

 

[Cole@MBS]

I suspect it’s the air pump, I also suspect if I’m right there’s also an air leak on the system somewhere, a read of the fault codes might show you the way! Most of the time it’s a seat or the boot lock leaking!

 

[DaveG38]

The saga of the strange noise is now complete, apart from an actual repair, and is quite peculiar.

First of all, many thanks to Cole@MBS for correctly identifying the source of the noise. What I subsequently discovered is that the boot soft close wasn't working. It could be opened via the door switch, via the remote and by old fashioned key in the lock, but closure only occurred by slamming the lid down firmly. Aha, I thought, clearly a leak in the air from pump to the diaphragm operating the soft close. Oh, no it wasn't!

I then found the battery to be totally flat, and non-chargeable - 9.7 volts, so dead. Out come the AA to fit new battery. AA man is concerned about a power drain from the pump causing issues with the battery down the line. I also mention that I won't be able to get the car booked in for the work for at least a couple of weeks, so I suggested pulling the fuse for the central locking, and relying on 1960s technology of keys and manual opening of the doors. Out comes fuse 62, off goes the pump and all doors work fine, as I bask in a fit of nostalgia for my old Ford Anglia!

New battery in, tested for drain - less than 0.5 amps so all OK. AA man then suggests putting back the fuse to see if this results in any kind of reset. In goes the fuse, up starts the pump, and then it stops. Down goes the boot lid. Hey presto, soft close is working. Result! Except that a check on all the doors shows the soft close to be OK, except on the drivers door. Curious, since before finding the boot lid problem and the permanently running pump, the driver's door soft close was working fine.

So, final result seems to be that I need to repair the drivers door close mechanism. All else seems OK. Out of interest, can anybody explain what was going on here?

 

[peterws1957]

The saga of the strange noise is now complete, apart from an actual repair, and is quite peculiar.

First of all, many thanks to Cole@MBS for correctly identifying the source of the noise. What I subsequently discovered is that the boot soft close wasn't working. It could be opened via the door switch, via the remote and by old fashioned key in the lock, but closure only occurred by slamming the lid down firmly. Aha, I thought, clearly a leak in the air from pump to the diaphragm operating the soft close. Oh, no it wasn't!

I then found the battery to be totally flat, and non-chargeable - 9.7 volts, so dead. Out come the AA to fit new battery. AA man is concerned about a power drain from the pump causing issues with the battery down the line. I also mention that I won't be able to get the car booked in for the work for at least a couple of weeks, so I suggested pulling the fuse for the central locking, and relying on 1960s technology of keys and manual opening of the doors. Out comes fuse 62, off goes the pump and all doors work fine, as I bask in a fit of nostalgia for my old Ford Anglia!

New battery in, tested for drain - less than 0.5 amps so all OK. AA man then suggests putting back the fuse to see if this results in any kind of reset. In goes the fuse, up starts the pump, and then it stops. Down goes the boot lid. Hey presto, soft close is working. Result! Except that a check on all the doors shows the soft close to be OK, except on the drivers door. Curious, since before finding the boot lid problem and the permanently running pump, the driver's door soft close was working fine.

So, final result seems to be that I need to repair the drivers door close mechanism. All else seems OK. Out of interest, can anybody explain what was going on here?

Might be worth removing the boot lock to check for damage and leaks. Resetting the pump by removing the fuse and replacing it may only work for a short period. If it's the same as the R230 there are in effect 2 circuits in the boot lock one operating the soft close and the other the central locking. A leak in either causes weird problems. The battery drain may be unrelated to this problem but only diagnosis would say.

 

[mioba]

Id scan for codes. Surely something will come up.

Many faults dont trigger an on screen message and sometimes you will be surprised.

 

[alexanderfoti]

The saga of the strange noise is now complete, apart from an actual repair, and is quite peculiar.

First of all, many thanks to Cole@MBS for correctly identifying the source of the noise. What I subsequently discovered is that the boot soft close wasn't working. It could be opened via the door switch, via the remote and by old fashioned key in the lock, but closure only occurred by slamming the lid down firmly. Aha, I thought, clearly a leak in the air from pump to the diaphragm operating the soft close. Oh, no it wasn't!

I then found the battery to be totally flat, and non-chargeable - 9.7 volts, so dead. Out come the AA to fit new battery. AA man is concerned about a power drain from the pump causing issues with the battery down the line. I also mention that I won't be able to get the car booked in for the work for at least a couple of weeks, so I suggested pulling the fuse for the central locking, and relying on 1960s technology of keys and manual opening of the doors. Out comes fuse 62, off goes the pump and all doors work fine, as I bask in a fit of nostalgia for my old Ford Anglia!

New battery in, tested for drain - less than 0.5 amps so all OK. AA man then suggests putting back the fuse to see if this results in any kind of reset. In goes the fuse, up starts the pump, and then it stops. Down goes the boot lid. Hey presto, soft close is working. Result! Except that a check on all the doors shows the soft close to be OK, except on the drivers door. Curious, since before finding the boot lid problem and the permanently running pump, the driver's door soft close was working fine.

So, final result seems to be that I need to repair the drivers door close mechanism. All else seems OK. Out of interest, can anybody explain what was going on here?

Pulling the fuse resets the fault in the PSE pump. The pump then runs as normal until it realises there is a leak in that branch, then turns off that branch.