I have noticed that my wagon hums when I turned off the engine. It is a low hum coming from the engine compartment for about 10-20 seconds after shut-down. It doesn't do it everytime though. Odd or normal?

 

I'd guess the SBC pump.

 

ours does. more noticeable on start up. I have a related question. I hear a small on - board air compressor. Identical to the GM car we had with air shocks. I do not have air adjusting suspension. The car is a stock E-320. I have never read anything in the literature about this car (2003) that mentions air shocks. Am I mistaken? If not what, is the little compressor doing when you bump it while the car is at rest?

 

Ahh. what SBC stands for?

do you have a wagon? the wagon has auto-leveler and adjusts the height based on the load.

 

Sensotronic Braking Control (Brake by wire computer directed braking system. Euro versions have a couple of extra features activated in their systems.)

 

The SBC unit is basically a hydraulic pump. M-B tried for several years to use this is lieu of a vacuum assisted brake set up because it allowed them to integrate brake control into a stability program run by the car's computer. I am guessing the pump allowed quicker input and faster response. They have experienced failures on some high mileage cars (taxis) and have dropped the system. To their credit, they have increased the warranty on this thing to 10 years. Even if you are a second owner, you should get a notice about it. It is very pricey to replace. It makes a high pitch whine that changes frequency from time to time and is more noticeable at idle when cold. I think it is only active with ignition on, The little compressor I hear is a lower frequency and can run at any time (ignition on or off). If you shift the car by closing a door etc. it will activate and run a few seconds. I suspect that is what you hear.

 

Didn't it also allow the car's computers to add throttle while braking wheels individually if that's what was necessary to regain control of an out of control vehicle & point the car back in the right direction?

 

I do not know what capabilities the computer has to correct skids etc. The SBC unit has enough brake lines coming out of it to assume that it can control each wheel individually. If the car is smart enough to correct skids, (ESP?) I am impressed. But then I was (am) impressed with ABS.

 

Its like the GM V8-6-4 engines introduced years ago. They didn't work as planned, and weren't an efficient use of dollar allocation at that time, so they were dropped. Today, (many years later) the system works is standard equipment in many GM cars & trucks, and is dependable and cost effective. Its just an example of an idea that was ahead of its time.

Hey, ya gotta stretch to grow.