J spaulding

I am still getting a P0410 based CEL (secondary air pump) and have done most things to fix it already. I have checked the 40 AMP fuse which is OK. I have replaced the relay (bought from MB) which is in the fuse box behind the passenger seat and put it in fuse position N which is recommended in the Parts book. After all this, the secondary air pump now runs constantly so I unplugged it at the pump. Obviously the fuse on down works fine so my only thought is that the relay won't turn off the power for some reason. Any suggestions?

J spaulding

Further work on my PO410 problem (secondary air pump problems) led me to a learning experience. I did a continuity test across the two terminals of the pump motor which is pretty easy to reach. The positive terminal is the bottom one. I ran two wires from the battery
over to the pump leads and.......nothing. The resistance reading was 5.3 megs which is basically an open circuit across the pump motor. I ordered a replacementr pump (rebuilt) from TEMU.com for $78 which was ordered from Asia by my Bosch part number 0 580 000 025 for 2007 SL550. The correct part number item came about 8 days later. I put 12 volts to it and it sounded great. My old pump rattled once I got it off so something insider broke. I installed the new one and turned on the key on a cold engine. The secondary air pump is supposed to run on a cold engine for approximately 40 seconds. My new pump started running.....and running. It wouldn't stop. So I figured that the relay was toast and because these are not particularly expensive ($44 even at the dealer) I bought it from the dealer after they showed me their Parts Department catalog page that said "Right, N socket ". This particular car is new to me (sold my outstanding CL500). I went looking for the 'right' panel/socket to install it and searched for "N' socket by pulling out about 8 different relays looking for N. The letters are cast on the relay mounting plate right under the relay station itself between the receiving terminals on the plate. You have to take out the relay to see the letters. I finally found the right side N socket on the fuse box that is under the passenger side storage bin behind the passenger seat. I installed the new relay in this 'right, N" location and started the car. I noted no change to the constant running situation and my Foxwell 510 Elite (excellent MB analyzer)" would not clear the CEL. I thought that this relay should have been in the engine compartment so I went looking and finally found that skinny fuse box right next to the right side hood hinge in the engine compartment. After taking out most of the relays I spotted an "N" socket but on my car it didn't seem to be occupied. Logic would say that I should use the N socket anyway which precluded taking out the M socket. It wouldn't start with M relay out so the best way of locating the correct N socket relay was to go looking for a relay of
the same part number since every relay has its own P/N on the relay body. I found another relay with my original P/N A 000 982 80 23 relay but in the left engine fuse box. Replacing that relay with my new one solved all of my P0410 problems. I am running for "dumb *** of the Year" so I would appreciate your vote.