I just got an 04 c320 about a month ago with 100k miles. It's been a beaut so far. However last week I got the P0104 secondary air error message. After doing some research that error translated to a faulty air mass sensor. So I bought a new one for $150 and wiped the error with a reader and no issues until today. That pesky error message came up again. Does anybody have any info what could be tripping this error? I would hate to take it to the dealer and them say it was something easy then charge me $300 for my trouble.

 

Was the one u bought bosch bbrand? If not that's not goin to work

 

Yep its the Bosch one. Got it from orielly's.

 

that sucks try to look for loose or broken vacuum lines

try to avoid the dealer and call around and ask shops if they have carsoft or SDS diagnoistics

 

Thanks. I did notice the elbow shaped duct can easily get knocked loose on the throttle body. I was gong to put a clamp on it to keep it in place. Don't know if there was one originally. I will check the vacuum lines.

 

that will throw a code if that hose gets knocked off

try securing that down and reset the code again

 

I would return it for a new one, maybe you got a dud.

 

Replaced the clamp hopefully that will work. I have a feeling the previous owner had this same issue because the plastic ring that goes around the maf housing was zip tied down. I did think that a vacuum leak could be causing it but the idle seems fairly smooth. I did notice there is a hard line that t's off from a vacuum line that runs to a sensor on the front driver's side of the engine compartment. Im not sure what this sensor is called but perhaps this is my culprit. I had the same issue on a mustang I had a few years ago.

Is there a way to test where exactly the error is coming from or to test the sensors? I really don't want to get another MAF sensor. The part store said it would be a week to get in. Besides if it turns out to be something else I can get my money back and reinstall the old one.

 

the only way to test the values on the sensors is to have STAR diagnostic service which is what the dealer has or carsoft

dealers are a hit and miss since they lie

call around to different mercedes shops and ask them what diagnostic systems they use

this is the only way to save u money and time

 

I read somewhere that there is a factory cd that I can get from the dealer. Might be well worth the investment. There is only one MB dealer here within 100 miles.

 

Ok so I clamped the elbow duct to the throttle body and the check light stayed on. So I continued to drive to work and within 30 min the light went out so success.

Then when I went to lunch I was sitting in the drive thru lane the car made a low whining sound and the check engine light returned. Now it continues to make that noise still. I'm fairly confident it is a vacuum leak. Correct me if I'm wrong but there should only be 3 places where the vacuum line connects to something, the 2 heads and the t line in front of the maf sensor.

Is there anywhere else it could be leaking?

 

Hi Boet, how would you explain the wining noise?

 

It's more like it runs a bit rougher and the mpg rating drops a few. It's not real rough so I don't think it is plugs.

 

I had a similar problem a while ago and after spending a lot of money chasing the problem, I , by chance, found that the cat's were blocked. I had that fixed and she's running like a true sportscar now. Km/l exelent.

You can check you exhaust header first to make sure it didn't split and try it . I don't say it is your problem but it might yust save you a LOT of money.

I am not a expert and cannot afford to take her to MB so to me it is trail and error.

 

I will be happy te explain what I did.

 

But would that cause the issue to come and go? Could be ill take a look in the morning. I will note that it looks like the driver side head was removed at one time because there is orange rtv selant everywhere including one of the hose. Pretty sure this wasn't a factory job and looks like crap. Maybe I'm leaking there.

 

Any suggestions are welcome here.

 

Bro I was at wits end and ready to give up. To answer your question - Yes.

Engine light resseted it self after cats were cleaned.

 

I might ad that I searced this site extensively for a answer before the light was switched on.

 

Awesome. Hopefully that will fix it. Did you take it to a muffler shop to get it done? I've done many of searches on here. Each one takes me in many different directions. It's not running bad but not great. It's more of an annoying light that won't go away. I've got a bb corvette and a vintage enduro that I regularly wrench on for fun but these computer cars drive me crazy.

 

I don't know where you stay and you might have to replace ypur cats but yes I took mine to a exhaust shope where the owner, to cut cost, cleaned out the existing cats to make it similar like a free flow.

You must follow steps to reset computer though.

 

I think I just found my culprit. I removed the elbow shaped duct and the hose that runs to it from the head was brittle and cracking when I removed it. Awesome if that's the problem but boo that I have to be at work before the part stores open tomorrow.

 

Pray it is your culprit. If not try it

 

It's all good. Just means I'm busting out the enduro to go to work cause that hose is trash. It's ok supposed to be in the low 40s. Perfect riding weather. But that is a good idea about the cats. Ill still get them checked.

 

Enjoy