David N.

My car is now making a rattling noise underneath in the area circled in red (please see attached picture).

I've done a lot of searching and it seems that there is a debate as to whether or not these two things circled in red are secondary catalytic converters.

Have we come to any consensus yet on what they actually are? If they are not secondary cats do they need to be replaced even though they are rattling?

The dealer wants $1000 a piece for both sides, to replace the entire pipe, just for parts.

Trying to figure out if I should leave them or fix them.

Thanks!

hanknum

Yes, those are your secondary cats. Before you replace them, find out why they failed...you don't want to replace just to have them happen again. Did they overheat? If/when you replace, you have to replace with same. If you still pass your emissions test and can live with the noise, then just keep them as they are.

David N.

Thanks!

In terms of why they failed, good question. The car is 10 years old and is driven daily 3 miles (5KM) one way to work and 3 miles back home (I know, short drive!).

I am thinking the combination of age, plus short driving distance, plus the primary driver of the car drives gently may have something to do with it.

I do hate the noise as the car sounds like a jalopy! But the price to fix is steep.

Glyn M Ruck

The most common cause of a broken monolith inside the Cat case is hitting speed bumps or potholes really hard while the Cats are incandescent.

contact148

check your O2 sensors my 03 c240 was rattling like mad i also thought cats but one of the o2 sensors had come loose tightened it up and problem solved

David N.

Good to know! Thanks to you both. :-)

When I had the car up on the hoist, I was tapping on the area circled in red with my hand and it made the same rattle sound I'm used to hearing. With that said I will check to ensure the O2 sensor is on tight.

MBfinatic

I have some extra cats that I will sell you . Pm me!

David N.

What is everyone's opinion of re-manufactured OEM cat's? One of the local shops here told me that could be another option worth exploring to save some cash.

selwyng

Hi David

Just some info.. I had the catalytic Converter removed from my vehicle (2001 C180, M111 engine). The reason i had it removed was because of the rattling noise. I just had a straight piece of pipe fitted in place of the catalytic converter and a "CAT BLOCKER" was used to fool the O2 sensor/ECU into thinking that the catalytic converter is still there (In South Africa there are no emmision control regulations etc)

However, after removing the converter there are very strong petrol fumes coming into the cabin of the vehicle. I cannot drive with open windows because of the petrol fumes. I have no CEL etc. I'm yet to take it to a mechanic who has the Star Diagnotics.

Im just sharing my experiences...

David N.

Thanks for sharing your insight. This is why I am apprehensive about putting in anything other than a brand new OEM replacement part.

hanknum

I don't think rebuilt or aftermarket cats are a problem. Any reputable one should come with a warranty. I've had aftermarket cats on my Ferrari for almost 15 years.

MBfinatic

I have oem ones for sale!

tommy

Magnaflow does make cats for your application, David.

I've had very good success with mine that I've had on my car now for over 2 years. Might be an avenue you might want to pursue.

David N.

I did some searching and read some folks were not too happy with their after-market cats. I guess I'll do some more reading on them.

Funny enough, I did search the magnaflow website and found an applicable part for my car. However none of the actual retail websites that sell magnaflow carry the part.

David N.

Indeed you do. As I do more research on this topic, I am paranoid to stray from model years. For example, the dealer sells brand new cats for an '03 C240 for $400, whereas an '02 is $1000. Why the price disparity, I don't know. Neither does the dealer. But based on my vin, only the $1000 part is showing in the system as being applicable for my car which makes me reluctant to buy any cat that is not for my model year specifically.

tommy

I had the same results when I looked at lunchtime; wonder why - might be worth a call to Magnaflow to find out.

EPineda

MBFinatic, do you still have the oem cat converter. Will it fit my 2004 C240 4Matic? My right secondary cat converter is rattling as if something is loose inside when you tap it hard and when idling. Email me at empineda@gmail.com if you still have them, at least the passenger side anyway.