Snap!
As an update on my cat problems, I eventually decided to have new lambda sensors fitted to my SLK320, at vast expense (£130 each). The engine was throwing a code indicating that the nearside cat was not working correctly, so I decided to have both the pre-cat and post-cat sensors changed in the hope that it's the sensors rather than the after-market cat. Touch wood, it seems to have done the trick.
This got me thinking about what happened. The first cat went at 15k miles (nearside cat broke up) and Mercedes replaced it under warranty. Presumably they didn't replace the sensors - they just did the minimum they could get away with. This cat then broke up (nearside again) after 8k miles. My theory is that one or both of the sensors on the nearside were faulty (probably the one before the cat) and this caused the cat to overheat and break up. The engine light didn't come on when they replaced the cat because the Merc cats are so over-engineered that they can clean up almost anything. The new cat was not over-engineered and so the post-cat sensor started complaining fairly rapidly.
The moral of the story is that one should always check WHY the cat broke up. But how was I meant to know this? Why didn't Mercedes check this when the first one went. When the second one went in the same way why didn't they put 2 and 2 together? (Answer: they couldn't give a monkey's). I think I'm going to be going back to Mercedes with a few questions.
As an update on my cat problems, I eventually decided to have new lambda sensors fitted to my SLK320, at vast expense (£130 each). The engine was throwing a code indicating that the nearside cat was not working correctly, so I decided to have both the pre-cat and post-cat sensors changed in the hope that it's the sensors rather than the after-market cat. Touch wood, it seems to have done the trick.
This got me thinking about what happened. The first cat went at 15k miles (nearside cat broke up) and Mercedes replaced it under warranty. Presumably they didn't replace the sensors - they just did the minimum they could get away with. This cat then broke up (nearside again) after 8k miles. My theory is that one or both of the sensors on the nearside were faulty (probably the one before the cat) and this caused the cat to overheat and break up. The engine light didn't come on when they replaced the cat because the Merc cats are so over-engineered that they can clean up almost anything. The new cat was not over-engineered and so the post-cat sensor started complaining fairly rapidly.
The moral of the story is that one should always check WHY the cat broke up. But how was I meant to know this? Why didn't Mercedes check this when the first one went. When the second one went in the same way why didn't they put 2 and 2 together? (Answer: they couldn't give a monkey's). I think I'm going to be going back to Mercedes with a few questions.
