Originally Posted by lilcobrar

I have a c280 with the same exact problem....did anyone ever figure this out ??? Thanks alot.

Originally Posted by dcsimmons

Our 2006 MBZ E-350 stopped all of the sudden headed down the interstate. The engine light came on a while back, but then went off. When it cane on, you could feel every distinctive stroke of the engine and so I suspected it was a camshaft sensor. Several months later, the engine light came on again, and scanning the codes showed a camshaft sensor going bad. By the time I purchased one, the problem went away again. But it came on again a week ago. It was my expectation to replace it when I had a free minute to do so.

I knew a bad crankshaft sensor would keep your engine from running, but I didn't think a bad camshaft sensor would. Nonetheless, I put the scanner on it to find out which one it was and replaced it. Nothing changed. Out of the possibility that I replaced the wrong sensor (there are mixed messages on which one is bank A, B, etc), I decided to replace them all (4 all together), and it still changed nothing. There were no other codes. I reset them, looking for a new one to show up, and nothing. No codes, nothing. Cranking it over does nothing. It doesn't even try to start, and no new codes. I don't believe a bad fuel pump or fuel relay always shows up (no feedback to the system), so I assumed the non-starting problem wasn't the camshaft sensor and headed to find out if it was getting fuel or not.

I checked and there was no fuel pressure on the fuel rail, so I suspected a relay since both pumps were replaced a year ago (VDO) and I couldn't imagine one going bad already. I checked the fuse and relay in the trunk, and the fuse is good, and the relay appears to be working fine as well. Both "switched" on poles went to 12 volts when turning the key on.

On the red wire of the main plug that goes to the pump (see attached picture), voltage switches off and on correctly with the relay, and I can hear the passenger side pump turn on and spin sounding normal. So it is a safe assumption this relay is working, and this pump is working or at least coming on.

I never hear the drivers side pump do anything, and I even purchased a brand new one, plugged it in (without putting it in the tank), and it makes no sound at all either. The passenger side spins normally.

So I have come to the following conclusions:

1.) The fuel pump (driver's side) senses whether it is in the tank or not and in gas. (I don't think this is it)
2.) It gets its power from a different wire than the provides the 12 volt to the other pump (the Red wire #2 on the plug) (Don't think this is it unless it gets its power from the pressure sensor plug)
3.) It is so quiet you can't hear it when it is running (Don't think this is it).
4.) It only comes on when it senses pressure form the other pump (passenger side) (I don't think this is it either!

I really am at al loss here as to why it isn't coming on unless there is some logic in the system that controls it beyond having 12 volts provided to it or not. It make sense that would be the case to control the pressure anyway.

Any help would be greatly appreciated! The car is just sitting in a T Hanger for now and I need it back on the road.

If it is of any convenience to others, I have attached some photos. One showing how to by pass the relay, another with location of the fuse and relay. The rest are self explanatory.

Thanks!