I'm writing this post about my experience to hopefully save everyone an expensive and unnecessary repair to their SLK 350 and probably other MB models. The secondary air pump has nothing to do with how the car performs and it made me mad that I had to spend a chunk of change on this just so I could get my inspection sticker.
The check engine light came on on my 2006 SLK 350 around 43K miles. I went to Autozone to pull the codes and found the P0410 Secondary air pump codewas the culprit. I went to the dealer and they wanted $200 just to look at it (Park Place Mercedes) after I told them I already knew what the problem was.
I started searching and found similar issues. I wanted to find out what caused it. I bypassed the fuse and found the air pump was pulling almost 100amps, wow!! I pulled the pump, opened it up and found it was fried. There was black dust all over the cover and I even found pieces of copper windings. The cause IMO, burnt contacts on the relay "O". While I was diagnosing the problem, I popped the cap off the relay and I could see the contacts were burnt.I checked with Park Place Mercedes parts department and they wanted $850 for a new pump and $38 for the relay
. Went online and got the pump for half of that and the relay for $6.
I installed the new pump and when I tested it I was surprised to find the pump was pulling +-40amps while it was injecting air (first 30sec from a cold start) and about 22amps when I ran it while the valves were closed and it wasn't able to push air (direct connect from the battery, the pump blades stall and uses less power). I immediately thought there was something wrong and that the Amperage was way to high and it would burn up the pump motor again (I couldn't find any specs on the motor of how much current it should draw). I was worried there may be another bad connection, so I made a harness directly from the battery and found the pump actually pulls about +-40amps at 14.1V (that voltage is when the alternator is charging after a start). Personally I find this current draw way to much for the relay, harness, connectors and pump. To me it's just a matter of time before one of the components/connections fail again.
To save everyone $$$, my advise is to change the relay every year or two and check the contacts regularly. A $6 relay could save you about $500 in repairs if you do it yourself and about $1500 from a dealer.
While doing research on this I found other causes for P0410. If the relay and pump motor are fine, but the pump isn't pushing air, check the small blue check valve on the vacuum lines and that the exhaust valves are actually opening in the first 30sec after a cold start. Also check all connectors, the neg wire off the pump and the fuse and it's contacts. The way this system was designed, it's going to fail sooner or later. Check/replace the relay often and save some $.