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2012 versa sv 1.6

556 Views 12 Replies 6 Participants Last post by  Rjdnrd8420
417,000 miles.
Has P0420 code.
Measured temp at catalytic converter input at 2000 rpm, it was 410 degrees.
At cat output it was 415 degrees at 2000 rpm.
Suspect bad catalytic converter.
Any recommendations on decent replacement cats other than from the dealer would be greatly appreciated.
CEL was on yesterday, today is off.
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You compare O2 sensor 1 to O2 sensor 2 action to determine if cat is bad. If sensor 2 is close in action to 1 then the cat or sensor 2 are bad.
You compare O2 sensor 1 to O2 sensor 2 action to determine if cat is bad. If sensor 2 is close in action to 1 then the cat or sensor 2 are bad.
I have the exact same problem, 2012 model same trim. Pulling an OBDII, you're saying that if the readings on sensor 2 and 1 are close then the cat or sensor are the culprit? I want to make sure I understand as I go about diagnosing this.
Yes. Sensor 1 varies wildly as it switches from high volt to low. It crosses .5 volt to hit either .1 or .9 roughly and correct action.

Sensor 2 correct action is to stay somewhere around .5 volt with minimum moving around.

When the cat begins to go bad sensor 2 then slowly more and more begins to imitate the high/low ranging of the sensor 1. At some point the computer deems sensor 2 to be too close in action to sensor 1 and then it sets the 420 code.

Sensor 2 being pretty much in the middle or close shows the cat is efficiently removing all the high/low swings in the air fuel ratio after the burn.
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So I drove around for about 8 miles - cleared the codes first and watched the OBD reader. First, the P0420 went away from the saved codes but keeps lingering in pending, so replacing the MAF alleviated but doesn't appear to have eliminated the issue. Prior to replacing the MAF the P0420 came on right away, stayed on, and kept going.

The car has ~180k miles but prior to my friend buying it it's been fairly well maintained. The MAF has been replaced a few times according to CarFax but that's about it. My ODBII is an Ancel AD310 and it seems pretty reliable.

Based on what you've described my upstream sensor is labelled as on the tool as O2B1S2 and runs between ~.3v to ~.9v (observed via the tool). My downstream sensor is labelled as O2B1S1 and ran from 1.9v up to 4.4v. My cat got up to ~1140 degrees F, but did not cross that.

It seems like the downstream sensor is off-base on the readings - to ME that reads like a bad sensor... I would really appreciate any feedback there on my assumption.
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Upstream sensor BEFORE cat is ALWAYS sensor 1. Downstream sensor 2 is ALWAYS AFTER cat. Think about what upstream is to you standing by the creek; it is before you. Down is AFTER you. Sensor 1 sets the A/F ratio, sensor 2 monitors cat condition.

Some readers do get it backwards. Some will let you swap to get it right.
@amc49 - I understand that, which is why I think the sensor numbers got swapped - but I can't reconcile a potential upstream sensor (in the tool as O2B1S2) running ~.3 to ~.9v and then what I believe is the downstream sensor (O2B1S1) running from 1.9-4.4v. My assumption is that the downstream sensor probably needs to be checked and replaced.

Unless you can suggest something else I think I want to try to swap the downstream sensor and then run the scan again. If that fails to improve then I think the cat needs a swap, given the mileage.
Thanks for the information. Yes, original engine but I replaced transmission somewhere around 210,000 miles. I bought it in 2013 with 41,000 on it.
Question. Where is the best place to measure the voltage for sensor 1 and sensor 2 and at what rpm do I measure it at.
I was thinking about using a sewing needle to stick in the 5 volt wire at the oxygen sensor itself and connect my multimeter to the sewing needle with an alligator clip and watching the voltage that way?
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