is there any electrical or mechanical work i could do to fix my smog test before having to replace my catalytic converter?

Question

i have a 2001 mercedes c240. and the car has driven fine during my 1 year ownership. and now i have to get a smog check, and i keep having to go back to my guy to scan it because it keeps failing the catalytic converter and oxygen sensor test. sometimes the o2 sensor passes and other things give off a fail test. but the cat test keeps failing. so is there anyway around this incase the cats actually are fine so i dont have to spend 300-400 bucks to replace it? ive driven on the freeway at recomended speed prior to these tests, and am running out of ideas and time before my tags expire.

Whatchamacallit · Accepted Answer

Are you getting any codes? I presume the ODBII catalytic monitor is not ready - that’s what you are saying right? What do the O2 sensor readings look like before and after the catalytic converter?

Normally if there’s no codes for O2 sensors and both sensors are functioning properly, there should be a lot of switching activity in the upstream O2 sensor and very little switching activity in the downstream O2 sensor. That also indicated the catalytic converter is good. You get this data by having a scan tool hooked up to the ODBII port.

Now if the downstream O2 sensor activity mirrors what the the upstream O2 sensor is doing, then usually the converter is dead and needs replacing.

Kaizen · Answer

The only thing I could think of is an Italian Tuneup.  Otherwise, the cats may need to be replaced.

Dan · Answer

I’d just replace the cat 😾 and see how it goes. There’s not much you can do on a failing cat - but first I’d check if the failure was caused by it getting clogged up with oil (and if it’s even worth repairing) by taking your finger and seeing if there’s residue on / around the exhaust pipe.