How many cats in a 2007 Nissan Xterra?

how many catalytic converters on this car, and if one gets bad, how to tell? What to do as a cost sensitive senior and former US Marine vet?

Appears to have two. Have the codes read, that may tell you. As far as cost, you just have to shop around. But if one has failed, I would replace both at the same time. Just avoid the chain muffler shops.

There are four (front right, front left, rear right, and rear left.). The trouble code will likely indicate which side the bad converter is on, but it might not tell you front or rear, though there’s a possibility that it will.

It could also be a bad O2 sensor. If they’re 11 years old I might replace them first. You’ll want to do that anyway with new cats.

Do you live in CA? New cats are more expensive there.

Thanks alot. I’ve got an update from fellow vet and backyard mechanic.
He says (via his test), I’ve got bad (probably blocked) left front cat.

So, new Q?: Just change that one and new O2 sensors…?

(These cats are high cost for me…so one at time sensible.)

your car is similar to 2006 Pathfinder i have and it has 4 cats

two “upstream” (closes to the engine) cats have air/fuel ratio sensors, then two “downstream” cats have oxygen sensors which monitor the upstream cats performance

the downstream cats are not monitored in this design, thus will not make for “check engine light” or for any diagnostic codes

if you have P0420 or P0430 codes, SUPPOSEDLY it is connected to the upstream cats getting bad, but do not rush to replace these, you might want to replace downstream oxygen sensors first, clear codes and recheck, if you have returning P0420/0430, at that point you can condemn an upstream cat for corresponding code

I was very happy with “PaceSetter” aftermarket cats: these were exact fit, no welding required, they are made from stainless steel and they were around $180 on Amazon

on my 2006 Pathfinder, although I did not need to replace the downstream cat, I ended up replacing one, as the flange connecting to the upstream cat developed a crack from corrosion, which resulted in further OBD2 codes condemning the upstream air/fuel ratio sensor (since downstream oxygen sensors “smelled” the exygen from the leak), so I replaced downstream cat with PaceSetter too

after 1.5 years: all the cats are still in good condition externally - not sparking clean, but no rust so far, no emissions system related diagnostic codes either

for downstream oxygen sensors, I bought ones from eBay, $15 a piece and they work great so far, but they are not really critical for the engine performance

for the upstream air/fuel ratio sensors, I bought the Bosch direct-fit/OEM units for $80 a piece from Amazon: these are much more critical for proepr engine performance and I would stronly recommend using good units there if y9ou plan on keeping your Xterra

after you replace sensors, make sure to follow air volume self-learning procedures from: