Ok I have used the search and I also read a lot of posts, which can be confusing.
So my 2004 s430 has great heat when driving but at idle....luke warm at best. Now from what I read I thought for sure it was the aux coolant pump. So I ordered a new pump and duo-valve from MB, 234.00 my cost. So I did more research and learned about the diagnostic function. Ran the diagnostic and no codes stored or found. When I hit the res button with the car off my blower kicks on but blows warm air which looses heat quickly. Engine temps are well within the normal range so I'll assume the water pump and thermostat are ok. Only other abnormal reading was that the overhead temp sensor value, value 3 was 0,0. Now I thought that might be the problem but even on HI I have the same issue. Before I spend the money on a new pump/duo valve do you guy think that's the issue? Also if I run recirculation mode it stays warmer much longer

Ok that is completely conflicting information from what I have read. From what I saw the pump works all the time to keep colant flowing to the heater cores, since they sit higher than the rad/water pump. If it was the overhead sensor the heat would still work on Hi since it over rides the sensor, correct? I have found a lot of threads about this but no one posts once they solve the problem

Ok well I reset the system, no error codes still but I'm still showing a 0,0 value on the overhead sensor. I checked my printout from Benz and it looks like it had the same problem about 4 years ago and they replaced the overhead console. So I found a used one on eBay and I'm going to try that route first, then maybe solder the one that's in my car.

My question is can the bad overhead sensor cause the aux coolant pump to not function?

Just about a week ago, I had the same problem. I would bet it is your Aux pump. I replaced mine and it worked perfectly. Another thing to note is that the Auxilary pump and the duo valve are one assembly, but you can save a lot of money by taking out just 4 screws to separate the two and just buying the pump. I also bought mine used and you should make sure the eBay listing confirms it is working. Once you get the pump, you can test its function by hooking up an ohm meter; a working one should read zero (or very close) and your bad one will probably read in the 100s (mine read about 450)
It's not all that hard to replace and if you don't mind loosing a cup or two of coolant you can take off the pump without draining the coolant system because the pump is the highest point. It took me 1-2 hours.

Exactly what the poster said above is correct.

It's your aux pump for sure.

Buy just the motor (I bought mine on eBay I think) and you can easily unscrew the old motor and swap. The rest of the assembly doesn't fail - just the motor.

No need to drain coolant as he said.. put a rag underneath and you'll catch some of the spills. Then just top up the reservoir. Not much drains out.

By the way, I bought a NEW motor and I don't recall it being that expensive. I think the motor was made by Bosch and had their part number on it. I believe AutohausAZ sells just the motor. Wasn't worth buying a used one as they all start to fail as they get old, and you may find yourself replacing it again a year down the road!

Once it is replaced, the car is great. Lots of heat at idle, and the REST function works amazing (keeps car warm for 30 mins I believe, after the engine is shut off).

You'll realize you have been freezing at traffic lights for years. I actually had the temperature setting at the same temp for years on the climate control, and lowered it 2 degrees when I replaced the aux motor because it was getting too hot. The higher temp was compensating for the fact that it was blowing cool air at traffic lights when stopped.

Thanks I'm a bit nervous about installing the new one until the used overhead control unit shows up, I'm afraid it will run the pump constantly and burn it out.....is that possible? I could also just unplug the upper sensor for now, not going to use the roof in Pittsburgh's weather right now

If you are sitting in neutral, put your hand over a vent and rev the engine to around 3-4000RPMs and hold it there for a sec, if the air gets hotter, you need to replace the aux pump.

That pump is designed to run quite a bit, so you're probably OK to install it and let it run if it's only for a month or two.

If longer, install the pump now and just leave it unplugged. If I recall correctly, you can reach the connector by opening the hood (without having to remove any parts). So once you are done fixing your car, you can just plug in the pump.

Good tip by previous poster about revving the engine. That will tell you for sure. The heat should only very very slightly increase (almost no increase at all..barely noticeable) when you rev the engine. If it goes from cool to warm/hot with an obvious change, your pump is dead.

Another test (the one I used) is unplug the pump and drive around for a few days. If you notice a huge change and are freezing at traffic lights or start to get cold air blowing from vents, your pump was fine.

I suspect if you unplug your pump now and drive, there will be no change at all.. which means your pump is confirmed dead.

I couldn't even get mine to run when applying +12V to it. Totally seized up. When I removed it, I knew right away it was bad by just looking at it and trying to turn the rusty shaft.

Me being lazy. I'm having exactly this issue, can one of you post the part number so I don't have to go hunting it down?

OK since I live in Oakville and you're practically my neighbour, I took the time to look through my records for you

Here is the thread I posted on another forum regarding the problem I had, how to test for it, and how I fixed it.

http://www.benzworld.org/forums/w220...at-vs-aux.html

You will notice that someone else posted removal instructions. Also see the part where I cracked the cowl pulling it off -- you should look up proper removal instructions and take yours off carefully so you don't damage it. Wasn't expensive to buy a used one though so if yours isn't perfect get another one before you start.

Part # for the "Motor only" part is 2208350064

Google a photo of the above part #, and also look up "W220 aux water pump" photos. You'll see that the part # is just the motor, and there are 4 screws holding it on. You don't even have to remove the water pump from the car.. just the four screws and the motors comes off. Some coolant will spill out.

It's literally an hour job start to finish at most.

Look at my post on the other board about disconnecting it and running the car. If yours is bad and you disconnect it, things will be the same. If it's good and you disconnect it, you'll know as you will freeze at traffic lights!

Can't remember where I bought the motor but eBay, AutoHausAZ, FCP Euro and lots of other places sell them. Just buy the cheapest one as I believe they are all the same MB/Bosch motor.

Thank you very much! This is fantastic and almost seems too easy, you've described it so well!!

James

Well my used overhead console showed up and the thermistor in it is shot too. So I left it unplugged but I hate that I lose my keyless entry,interior lights and automatic lights.
Tomorrow it is supposed to be a high of 6 so I'm going to tackle the aux pump before work. The only thing that makes me nervous is taking the cowl plastic off. I don't want to crack it. Will I need to reseal it with silicone or anything? What causes it to stick?

Went to change my motor today and couldn't get the passager side wiper arm off the pivots. The drivers side had a cool metal sleeve that popped it off but not the passenger side. So I had to order the tool from Amazon, should be here tomorrow

Got the aux pump changed today! All in all a two hour job max. Hardest part for me was getting the rubber studs to slide into the bracket and getting the windshield wiper arms off the studs. My pump was defiantly shot when I pushed res I got nothing from it. Put the new pump in and bam motor started spinning the minute I hit res. Now to run the car with the resivour cap off to burp the air out and then a small refill from what little came out and I'm golden. Still need to fix the overhead temp sensor but that's tomorrow's plan.

Glad to hear everything worked out!