Bought the Sentra. Just failed Emissions

[ZedHead]

It had code P0420: Catalyst system efficiency below threshold bank 1

Any idea what this means?

I had it inspected at a Nissan dealership before I bought it, guess they didn't run codes on it. Fail. The guy told me that the exhaust was bent, probably from hitting a bump or going over a curb. Didn't think it was a big deal. This is probably what is causing it to fail. Possibly a leak even though I cannot hear it.

Input please.

Also, the nice gentlemen at the test station told me the check engine light was burned out on the dash. I assume I have to drop the steering column to get to it. Is this correct?

Thanks guys. Got the guy down to 2200 for the car, thought it was a good deal. I'm hoping the emissions repairs are fairly minimal.

[somecallmetom]

Sorry, replied to your old thread without noticing this one. With an error code like that it sounds like possibly one of your O2 sensors maybe faulty. Either the one before or after the catalytic converter. I'm no expert but that is my first guess. Also if they ran OBD2 scan to check and got the first error code, but no other errors the check engine light would be lit. The "Check Engine" light really is linked to your emissions system, and previous owner could have just ignored the problem. I wouldn't say its anything serious, other than possibly a faulty sensor.

[Wc240]

that code means the second sensor is switching the same as the first, hears cat monitor 1o1:

your first o2 sensor(pre-cat) switches from rich to lean at least ten times a second(10 HRTz) sensing the rich lean conditions. this is necessery due to the fact that the cat, to run efficiantly, needs constant switching. now, the second sensor(post cat) sences the gas coming outta the cat(duh) now this sensor is ONLY to make sure the cats doin its job. it SHOULD be at a constant(flat/steady) voltage. if it starts seeing switching/ rich/ lean conditions, the ecu takes this as the cats f***ed up, and your basically running a test pipe.a bent exhoust would contribute to this, unless theres a good sized hole in it before one of the sensors. hoped that helps

[p00kienrayray]

Zed, what year is your car? I doubt it's the o2 sensors. I'm going thru the same issue. Here's my breakdown:p0420 came up. Was told it was the precat. Ignored it and changed both o2's. Lite still on. Then realized the bottom of the precat had a small crack near where the collector flange was (looked like the previous owner hit something). There was a lot of air blowing out so I had it welded completely around and no more leaks. Lute STILL on. Then I saw water leaking out of where the collector flange meets pipe. So I changed the collector gasket. Lite still on. Yesterday I saw a black sooty area of the exhaust pipe where the flanges meet right befor the rear o2, which indicated another leak. I changed the donut gasket and am now waiting for the lite to come back on.

Pretty much I'm just looking for an exhaust leak or bend and fixing each little issue as I go to rule out any other possible causes before I step up and buy a $500 precat here in CA.

[p00kienrayray]

Pretty much your rear o2 is tripping the lite so watch out for any leaks between your exhaust manifold and rear o2 (which should be near your front axle).

[ZedHead]

Thanks for the replys everyone. I count 4 02 sensors on the car. You mention only two, one before and one after the cat. I have two before and two after the cat. The car is a 2000 XE.

I've done away with this issue by registering at my parents who are out of city limits. The car runs fine so I'm not going to deal with in now. Maybe when it warms back up.

Some other things I've found wrong with the car.

The left front strut is blown, rattles pretty bad over bumbs.

The thermostat needs replaced. The car warmed up fine when we test drove it. Its gotten colder now and does not warm up to opperating temp.

I think thats is. Easy to fix.

Thanks again everyone.