Last year my 2003 SL500 started having the rear trunk accessory battery go flat. The battery was replaced, and the new one was doing the same thing shortly thereafter, draining the battery within a day or two. I took it into the shop, and they told me there was definitely an electrical drain coming from somewhere in the car, one of the computer modules was apparently not shutting off.

After 12 hours of them disconnecting modules, unhooking this and that, they couldn't find what was drawing the current. But now I have an idea...

I heard my car in the garage one day make a noise that sounded like a generator, or a pump...making almost a grinding noise that lasted for about 3 seconds. I have heard this same noise previously at times when unlocking my car, but have noticed it also do it when I get in the car and my foot touches the brake pedal to prepare to start the car. My car makes this noise about once every hour now (on it's own) , so I believe whatever is making this noise is the source of the electrical current draw.

The noise comes from under the hood, it sound like it's slightly on the passenger side, but not 100% certain. Since I have noticed this same noise when I get ready to start the car and hit the brake pedal, could this be related to a booster pump, or some part of the brake by wire system generating some sort of pressure?

I'm dying to get this resolved, because I can't afford another 12 hours at the repair shop without resolution, and I can't leave my car off a trickle charger for more than 24 hours or the battery goes flat.

Thanks in advance for any help.

 

Through some more research, I found out that it is the SBC pump that is making the noise. I have noticed that I hear this pump about once every hour in my garage. It is consistent, and my battery will drain consistently within a day or two.

So I'm wondering if this is a faulty SBC pump that needs replaced, or is this likely a module that is not shutting down? The service center said that there is something pulling a consistent current in the system, but tehy couldn't locate which module was doing it.

So is it safe to assume the module that is in-line with the SBC pump is not shutting off ?

 

SBC PUMP HAS CURRENT WARRANTY TO 100,000mi. TAKE IT TO A DEALER AND SEE IF SOFTWARE HAS TO BE UPDATED. THEY CAN ALSO INSTALL A NEW SUCTION HOSE WITH VIBRATION DAMPENER WHICH WILL SNUFF OUT MOST OF THE NOISE BUT NOT ALL. BATTERY DRAIN IS MOST LIKEY A CONTROLLER AREA NETWORK (CAN)ISSUE ESPECIALLY SINCE UNPLUGGING ALL CONTROL MODULES IS NOT SOLVING ISSUE. I HAVE YET TO SEE A SBC PUMP CAUSE A DRAW, BUT YOU CAN'T RULE ANYTHING OUT. I WOULD TAKE TO DEALER BECAUSE WE HAVE A SPECIAL SOFTWARE PROGRAM THAT CAN ISOLATE DRWS ON THE CAN NETWORK IN SAY 2 HOURS INSTEAD OF 12. BUT ALWAYS REMEMBER BATTERY DRAWS SUCK AND CAN TAKE TIME.