I had good luck with this stuff years ago in another situation, and it seems to have solved my issues this time.
Amazon.com: deoxit 5

I was getting a P0410 code every 6 months or so. It got more frequent, with 2 in a day being the last straw.

I used it on the male & female ends of the 2-pin pump connector, the small connector at what looks like a solinoid valve with the blue vacuum check valve next to the pump, the big fuse at the RCM and the ground wire under the bolt head on the pump.

It helps to spray it into the cap and apply it with cotton swabs with 1/2 the cotton removed, especially in the female sides.

I waited a while to post this, and no code so far!

 

This problem has occurred before because of corrosion on the ground wire terminal.

 

That may work for awhile but the issue is the relay in the RCM.
Which by the way I now replace for a nominal fee.

Just sayin'!

 

I get the idea I should order some of those relays.

 

Back Off Marky Mark!
I wuz here first!

 

I also had luck polishing the relay contacts, but that is also a temporary measure. Do we know if the low voltage that causes the relays to carbon up is generally a result of the solder joint issue, or is this usually due to the crossfire being especially picky about battery health?

 

Does anybody have the part number for the relay itself, not the RCM assembly?

I see that others here make money repairing RCM's for others, please forgive me if I am stepping on any toes by asking.

 

AZ970E-1A-12D American Zettler | Power Relays (20 Amps to 99.9 Amps) AZ970E 1A 12D | Onlinecomponents.com

Here ya go.

 

If paying postage and a tip for a beer is charging....well....lol

 

No he wasn't, I wuz.
I even shipped some relays to 180 while you were out .

 

Dang. Dave beat me to them lol.

 

You went AWOL for a while and we carried on. The relay was replaced by ala_xfire ages ago. You have to catch up.
I have some relays just in case, courtesy of ala_xfire. I did do some groundwork on this way back.
Relay Replacement PDF

We have relatively new members who play with the brains of the car.

This ain't no Mickey Mouse forum, we'se reelly, reelly sofistigated now.

 

I think he makes enough for a beer and that's it, he ain't got no plans for retiring on the proceeds.

 

You guys are AWESOME!

Thank you all so much for your time & effort. You all already made me look like bloody Nostradamus to my co-workers when the CPS failed during my morning commute and I had spare one & tools in the car already.

One last question, please.
Do you find it worth changing other relays in the RCM at the same time as the seconday air item, do any of the others wear out as quickly & cause issues? I don't imagine the horn or traction control relays get used much, but what about the fuel pump & engine control?

 

Only the air pump relay is an issue.


UPDATE!!!!
Fuel relay coils have been failing so now two relays to worry about.

 

Yesterday I ordered some relays, intending to repair my RCM.

Today on the way home I went by a wreckers that has an SRT6 to get a spare RCM. The car's hood and the cover to the box the RCM is in were missing, the RCM had become full of nasty water and was junk. I am glad they let me go out to the car, supervised by a yard employee.

I asked the guy at the counter when I retured if he had a SLK320. He said yes, and asked if the employee that went to the SRT6 with me knew what I needed. I said yes and he went in the back to send him out to get it (without me).

The item he returned with was a different P/N (W210, E class?) but other than the single 20A fuse in my RCM being a 15 in this one, I could not tell any external difference. The pins etc... were identical. It was cheap enough that It was worth the gamble and I bought it.

The car threw another P0410 code on the way home!

I opened both RCM's up and my old one has pitted contacts on the air pump relay, the new one looks good. My old one has the "mystery no start" solder that does not look very solid, the junkyard item appears much stronger.

I really scrutinized them both inside & out trying to find anything different between them, but they really seem the same. I switched that one 15A fuse for the 20A to match the Crossfire RCM and installed the junkyard RCM. So far so good, everything seems to operate OK.

Has anybody else found/used a MB RCM with a W210 P/N? Am I flirting with electrical disaster?

 

Turbomar used the same RCM with no problems. CLICK

 

Thanks guys, it has all worked out well, no P0410 codes after 1000 miles on my repaired RCM. This car is my daily driver, your help gets me to work.

I bought a few relays per your information.

I used the the "W210" (inexpensive) junkyard RCM as a backup during repair of my original RCM without issues.

An aerospace spark-chaser friend changed the air pump relay on my original RCM and re-soldered the "mystery no start' connections (they looked bad under magnification).

I then re-installed my now "repaired" orgininal RCM, stowed the junkyard item as a backup with the spare CPS in the box 'O stuff I keep in the car, and it all seems to be working well.

 

Thanks for all the tech help guys. I'm pouring over it now to get rid of the same code. Did I read about a high mileage club?...130,000 here. Just got it a week ago. Code started today. Peace

 

We got rid of the code by filing the contact points of the relay with sandpaper. They were burned and noticeably looser than the other relays on that board. I would never have known to go to the relay box and pry off the cover if I had not read about it here. Thanks for the tech info. Peace