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I have an old 2000 Honda CRV, where the 18 year old exhaust is on its last legs and in need of a full replacement. The B-pipe bolt mount on the catalytic converter has rusted off, and the cat heat shield has also rusted off. The B-pipe is currently directly welded to what remains of the old cat.

The vehicle otherwise runs fine, so I will probably get a new cat, heat shields, B-pipe, etc from some online place that sells inexpensive genuine Honda parts.

Apparently the A-pipe is not leaking so probably will keep that, as it costs nearly as much as the cat and it's just a short little stub of a pipe.

I see the oxygen sensors are about US$250 each and there are two of them, one on the A-pipe and one on the cat.

If the vehicle is running fine as it is now, and the check engine light is not on, is it necessary to replace the oxygen sensors with brand new as part of installing a new cat, or if they are working fine already, pull them out and reuse them?

I am aware the threads are likely seized and may strip trying to remove it, but seems worth trying, to save $250 vs a new O2 sensor.

  • If you can remove and reuse them do so, if you can't, sadly, open the wallet more... – Solar Mike Nov 30 '17 at 8:50
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If your Motor runs fine and fuel consumption is normal, there is no reason to change them. It is normally easy to change them if they go bad later.

If they are really hard to reach without disassembling you exhaust, you may reconsider. Also, often they are rusted quite firmly in place so make sure you are able to remove them from the old exhaust without damage.

If they are not rusted in after 18 years, chances are they have been renewed in the past.

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If the sensors are functioning there's no reason to replace them, however if they are original they almost certainly aren't functioning properly unless you have a low mileage car. You might not get a code for this, often you only get a code if the sensor quits entirely, not if it simply starts to be inaccurate, which is what happens when these sensors get clogged by emissions and degrade over time.

If it was me I'd replace them, without them functioning properly you will get poorer gas mileage.

You can test their functionality with a multimeter, there's how-tos on the web for that. Most of them require the car's exhaust system to be in working order, but there's ones that involve having them off the car. If you have the equipment and the expertise it would be worth your time, presuming you can get them off in the first place. If not it's academic.

$250 each is a ridiculous price for o2 sensors, that's a vastly inflated price from Honda. You should be able to get both sensors together for around $120, that's for Denso parts, which is the OEM manufacturer, although it could be NGK or Bosch. If you buy a sensor from Honda all they do is buy one of those manufacturer's parts, stick a Honda stamp on them and mark them up 200%. There are other brands, some cheaper and nastier but you should be able to get sensors from a quality manufacturer for $200 at most. At that price I'd replace both sensors personally, you'll make the money back through better mileage and pollute less.

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