Parkaide

I have a 2002 CLK 320 with a P0410 check engine light code that I haven't been able to solve.
First I did what I could do;
Replace a noisy Secondary air pump and check all the vacuum hoses
Then I took it to a Mercedes shop where they checked the air pump, hoses, etc. and found that the fuse box holding the relay and fuse for the air pump had a short so they replaced the fuse box. Still had the check engine light so they replaced the sensor ($280), still had the check engine light.
Now after spending over $500 I still have the check engine light. Now the Mercedes mechanic suspects that the aftermarket catalytic converters may be restricting the air flow so I am currently running some Cat Cleaner to see if that solves the problem.
I love the black convertible. It is in great shape but I won't be able to smog it in 5 months with the light still on. The car runs great but the mechanic and I are stumped. I would hate to have to replace the exhaust system to get the check engine light to go off. Any ideas?
Thanks, Bruce

Serndipity

Did anyone check out the air pump relay (K40/4k3) and 40 amp air pump fuse (K40/4f7) in the K40/4 fuse and relay module, which is inside the control module box, located in the passenger side engine bay?



It's the same multi-purpose relay that is used to power other electrical motors throughout the vehicle (e.g. fuel pump, hydraulic pump on the cabriolets etc.) and is inexpensive (e.g. about $8).

FYI: In the cabriolet, the same relay and 40 amp fuse power the hydraulic pump motor, where the relay fails, because the motor winding presents a highly inductive load when the relay contacts close, which is stored and then released as a high voltage when the contacts open, causing a spark that in time damages the contacts and the ability to start the hydraulic pump's motor.

At every cold engine start, the ECU supplies a rich fuel mixture (e.g.to assist engine starting) and the air pump runs runs for about 30 seconds, to lean out the engine's exhaust, prior to reaching the primary catalytic converters. As a result the cat's will last longer and the tail pipe emissions will meet the required U.S.A. emission requirements.

Many states follow the Federal DOT smog guideline requirements, so check if your state has an exemption for smog testing on older vehicles, such as the Massachusetts exemptions shown below.

MA will also waive the smog test requirement, based on the 'good faith' cost to repair being in excess of a certain dollar amountthreshold.




Note: The OBD test involves, successfully connecting and communicating with the station's computer and not having any diagnostic code troubles showing catalytic converter failure or engine misfires.