2002 E320 Door Lock issue in cold
 

Hi,
I have a E320 wagon with 67k miles that has a weird problem. The vacuum locks work fine when it is warm in the garage but work slowly or not at all in the the cold. This has caused the car to be robbed when a couple dorrs didn't lock correctly.
Any thoughts?
Steve:confused:

Most likely a leak in one of the vacuum diaphrams.
How long does the pump run?

I agree. Either a leaky diaphragm is robbing vacuum from the system OR the vacuum pump is starting to get weak and doesn't like being cold.

Listening for the pump running is the next step either way. When healthy, you'll hear it kick on after locking the doors and a second or so after the doors all lock, the pump starts to slow down as the vacuum rises, then quickly stops as the negative pressure sensor engages.

If it's leaking, you'll likely hear the pump run for a bit longer than normal. Once we verify that, the next step would be to remove the vacuum line from the pump and cap (seal) the pump. Running the same lock-time test this time, the pump should run only very briefly and shut off quickly since its output is now sealed. If so, then you likely have a leaky diaphragm as mentioned before. If the pump still runs a long time, or sounds like its struggling, then its probably the pump motor, or the pressure sensor inside the pump is out of whack.

I will check on this. I suspected a vacuum issue. Where are these diaphragms located?
Also where is the pump to listen to?
Thanks in advance.
Steve

The locking pump is under the back seat on the passenger side.

Are the diaphragms part of the door locks themselves then? Would the leak be revealed with a pressurized smoke machine?
Thanks. Sorry I know so little about this issue.
Steve

The pump runs for about 25 seconds initially then on subsequent locking and unlocking it is for about5 seconds. It doesn't sound weak.
Steve

I think I found the problem
 

So here's what I found: No leaks detected with smoke machine. I did find the doors all maintained vacuum for 4 hours with a Mity-vac attached. The fuel door has its own line and could not hold a vacuum. It had no detectable leak with smoke machine. It appears the diaphragm in the lock unit to the fuel door must be bad.

I plugged the port on the vacuum pump until I can get a new one.
Steve