thunderbirl

My ML threw this code and I've worked through it. I've got a couple questions.

The general code is P0410. I cleared it once and it came back. There are enhanced codes indicating the same problem with both banks. In my mind, this meant a problem with the controller for the pair of diverter valves and/or a problem with the pump.

Using my AutoEnginuity system, I tried to actuate the air pump. I could hear/feel the relay trip, but got nothing out of the pump. Inspection of the pump showed glop on the bottom of the pump suggesting that it might have, as noted in other posts, some water in it.

So I pulled the pump and there was half a cup of water in it. I tried to run it on 12 volts and, although I got some very minor sound, there was no whir. Eventually I blew the 8 amp fuse in the +12 line. Upon dissection, I found the shaft totally immobile and evidence of water up to the level of the motor.

Trying to make sure that I had control, I went back to the car and checked the feed to the pump using the AutoEnginuity. The relay clicked, but there was no power getting through the relay.

This is where I run out of knowledge. (I can't find the fuse listing/wiring diagram and have forgotten where I saw it tucked away in the car.) I'd heard that the 40 Amp fuse was the power for this circuit and that they could blow. I checked and found mine was open/blown. Given a locked up motor, I'm not surprised.

If this fuse is the power to the AIR pump, then I'll go get another 40 amp fuse and check the control power. If that's OK, then I'll spring for a new pump.

So my questions are:
1. Is the 40 amp fuse the power for this device?
2. Is there anything else on the 40 amp fuse?
3. How's the plan sound? (While the controller for both diverters could be bad, it'll be incremental to the pump- so I'm willing to fix what I can find for now and see what happens.)

Thanks for any help.

thunderbirl

The proximate cause of the pump seizure was a frozen front bearing - no doubt due to the water inside the pump. I was able to disassemble the motor, free up the bearing, reassemble and get the pump running on the test bench. In it's current condition, it's drawing under 5 amps, but is, rather, on the noisy side!

thunderbirl

For grins, I re-installed the old pump while waiting for new one to arrive. It was a bit noisy at first, but seems to have quieted down.

My question is "How does water get into these pumps"? followed by "Why not have a tiny drain hole in the bottom?"

I have put such a hole into the lowest point on my recovered unit and it seems to work just fine.

Any ideas?

thunderbirl

So I guess I'm going to do this one as a monologue!

It seems that the likely source of water is leakage from the exhaust system through the control or check valves.

I've got two of these.
Will I be able to feel warmth down the rubber connections from the valve to the pump to figure out which side is leaking?
Can these valves be cleaned? If so, how...

Thanks in advance.

ml3204me

You probably won't be able to feel any warmth coming down the rubber connections as the water is probably building up extremely slowly over time.

Keep at it and let us know what you find...

thunderbirl

At lunch I tried the temperature test...It's an experiment because I don't know if it will work. As you pointed out, if the leak were small - no way would the rubber hose be warm. It it's a rapid leak, maybe I would feel it.

Keeping in mind that it's really rather cold here right now, I drove the car for 15 minutes and then stopped in the driveway. I felt that the lower (passenger side) hose (beware the serpentine belt!) was cold. This doesn't mean that it doesn't leak - only that I couldn't sense it. I can't remove that hose with the engine running without risking fingers.

Checking the upper (driver's side) hose, I found it was quite warm. I peeled off the rubber hose on that side and could see a few drops of water in that hose.

This experiment may not have given the same results if the outside temperature were warmer. Given that rubber hoses are used, I know that it's never terribly hot at these points.

So, I'm pretty confident that the upper valve is leaking. There was no exhaust blowing out when I took off the hose, so I don't know how badly. I'm off to get some E-torx sockets to pull off the valve to see if I can clean it!

Then we'll figure out what to do with the lower valve.

thunderbirl

Removal of the left (US driver's side) control valve involves two e-torx bolts with a 10 mm socket. I had to remove the electrical connector for one sensor to get a clear shot at the rear screw. There is a very simple flat mating surface and gasket arrangement. Everything came off very cleanly.

The base can be separated from the actual valve body with three phillips screws and reveals what I think is some sort of a backfire/flash back valve seated in a rubber gasket. That simply knocks loose to reveal the actuated plunger valve.

Mine was leaking. You can't really see the sealing surfaces as they are recessed. The valved is covered in some sort of rubber which seems to have gotten messed up in some way. I cleaned as best I could and didn't get it to seal, so I ordered a new one.

Once that arrives, I'll replace the valve and the (still) noisy pump.

thunderbirl

I wanted to clarify this sentence in my first post, above...

The fuse referred to was in my +12 power supply that I have on my test bench.

The actual fuse for the unit is a 40 amp jumbo-size blade fuse in the engine compartment fuse block. It's # 107 and runs nothing but the AIR pump.

While I was, after dissection, able to get the motor running on the test bench, I can tell, having now put the motor back into the 40 amp environment of the car, that it was not getting anywhere near up to speed.

Still, a week later, the motor is still functioning, if a bit noisy - and even with a leaking check valve, I have no codes.

thunderbirl

All done and back together. It cost me an AIR pump, a check valve and a fuse.

In the final analysis, the AIR pump was damaged by accumulation of water condensing from the exhaust gas leaking back through one of the check valves. I know that it blew a 40 amp fuse when it went. Whether the pump died from repeatedly getting water in the bearing (it was seized quite solid) or from the water freezing the rotor and causing the high current draw, I'll never know. When the pump stopped working, as I understand it, the computer analyzed the O2 sensor signals to figure out that it wasn't getting any secondary air and threw code P0410. That was the only way that I knew there was a problem.

I must confess that I'm a little angry that the system is designed to trash a (list prices) $700 pump because a $200 valve leaks.

Prior to putting in the new pump and valve, and because I didn't want a repeat failure from water that I could see was condensing from a defective check valve, I drove for the past week with a couple small holes in the bottom of the resuscitated AIR pump. Those little holes seem to have been quite sufficient to allow drainage of water vapor from the exhaust leaking through th eone defective check valve. The holes seem to have made no practical impact on the delivered output of the AIR pump. (i.e., no codes)

If some form of water drainage port had been added during the pump manufacture, I probably wouldn't have had to replace the pump - but I also might not have known that the check valve was leaking. Surely a Mercedes engineer could do better...

Hope all this helps someone!

ml3204me

Nice write up! Definitely a pain point and a pump design that should be improved by MB.

I had problems with my secondary air pump as well and did a video on my experience:

sn3akyducky

I would do your self a favor and drill one small hole in both mufflers to drain water built up in exhaust. I see this often on 204 c classes and after replacing the fuse, pump, both check valves and drilling drain ports in mufflers I have not had any other issues.

thunderbirl

Please explain how one small hole could, even hypothetically, either:
1) reduce the water content of a stoichiometrically combusted air/fuel ratio, or
2) provides any meaningful decrease in backpressure pushing exhaust through the defective check valves - when the existing exhaust pipe is about 2" in diameter?

It's not clear to me why you might have replaced all those parts "often on 204 c classes" when it's unlikely that they were all defective - or ever would be.

What you've done is to replace the entirety of potentially bad parts whether they were bad or not and then, additionally, done something that makes no logical sense and attributed magical powers to it.

I'd argue that, in the absence of data to the contrary and given the MTBF for these parts, you have not likely had enough time elapse to where the check valves might actually fail! Hence, you cannot, realistically, have any verification of even the magical effect.

Your path is not my path. So, "no", I will not be drilling holes in my muffler.

sn3akyducky

Don't over think it. the condensation build up in the exhaust, which I'm not sure how it makes it way up to the air pump takes out the air pump. I replaced the check valves due to being exposed to all the water is going to be rusty and has a great chance to seize and fail. The two holes in the muffler are to simply drain the water out. If you chose not to take the advice that's fine. If you do I guarantee you will have water pour out. I've had a 211 fail to start because of water in the exhaust which turned to ice and blocked it.

thunderbirl

You're telling me "don't over think it", yet you are 'not sure how condensate build up in the exhaust makes it's way up to the air pump'. Wow...

What makes you think that water can flow against the exhaust stream and get from the mufflers back through the incredibly hot catalytic converters to a few inches down from the exhaust headers to cause a seizure in the control valves?

Why aren't frozen exhaust systems a significant problem in all the cars, or at least all the MBs in northern Canada and Scandanavia?

BTW, I don't disagree with the utility of a little drain port in a muffler - to keep it from rusting, but it has nothing to do with P0410 - and it's very unlikely to have anything to do with blocking the exhaust - unless someone ran water from a hose up the tail pipe in the middle of February.

If I may suggest, try thinking things over before telling others to not over-think things.

manwhatadork

thunderbirl, did you find it easy to remove the secondary air pump on your 2008? I need to do it on my 2010. I bought a copy of the Mercedes dealer repair guide and in that, it looks fairly straightforward. I think I will get the part via Ebay as it seems to be just a glorified hair-dryer.

I am in the Rochester area also. I hope the weather improves some so I can get this done without freezing my *** off.

thunderbirl

Everything was right on the front, not a lot of bending - pretty easy. Since there's nothing really hot near where you'll be working, you could warm the engine up before starting and enjoy the residual heat as it cools!

In 2008, there were five screws, three push-on rubber hoses and an electrical plug to remove the bracket and unit from the car. There were three screws to remove the unit from the bracket.

I believe all the screws were T30 heads. The biggest problem is that the ones on the lower left are set back and crowded a bit, leaving little room to grab them as they come out. I did have to retrieve one from the lower pan.

In the long term, the more important question is why did it fail? Have you looked for moisture at the check valves?

Yes, I got both the pump and the check valves through OEM dealers on Ebay.