SES Light On with P0420 & P0325

[it_cowboy]

2001 Nissan Altima GXE with 4 cyl. SES light came on about 70,000 miles ago (car has 144000 miles) and at first came and went on and off. Pretty much stays on all the time now. I pulled the codes at the time and since car ran fine didn't touch it. Now I want to sell it and need to get the light off LOL. Car still runs great so I figure its just a bad sensor. The P0325 indicates the knock sensor and I read several posts about them going bad. Just wondering if it went bad if it would cause the PO420. I've reset it a couple times to verify I still get the same codes, and I do. The knock sensor sounds like a major pain to get to to change out so I just want to make sure its the problem before I tackle that project. Any way to test it's voltage or resistance?

[tls1002]

p0420 is ur bank 2 o2 sensor that mean is the 02 sensor either on the cat or on the engine pipe and knock sensor for altima is always go bad

[it_cowboy]

So if one goes bad can it trigger the other to throw a fault? Or are they both probably in need of replacement?

[jserrano]

Originally Posted by it_cowboy

So if one goes bad can it trigger the other to throw a fault? Or are they both probably in need of replacement?

You will need to replace the knock sensor unless you find something like a bad wiring problem going to it.

The P0420 could be a couple of things. The greatest mayority of the problems comes from the catalytic converter or O2 sensors. There are rare ocassions where it could also be coming from an intake or exhaust leak, or even an ignition problem.

[jamirokev]

Originally Posted by it_cowboy

2001 Nissan Altima GXE with 4 cyl. SES light came on about 70,000 miles ago (car has 144000 miles) and at first came and went on and off. Pretty much stays on all the time now. I pulled the codes at the time and since car ran fine didn't touch it. Now I want to sell it and need to get the light off LOL. Car still runs great so I figure its just a bad sensor. The P0325 indicates the knock sensor and I read several posts about them going bad. Just wondering if it went bad if it would cause the PO420. I've reset it a couple times to verify I still get the same codes, and I do. The knock sensor sounds like a major pain to get to to change out so I just want to make sure its the problem before I tackle that project. Any way to test it's voltage or resistance?

Your not alone, this past Sunday my SES light came on, and I took it to autozone and I recieved the exact same two codes...<hmm> I have the same car with 107k on it. I cant take it to my mechanic until 7/24, so if you get it repaired before then please post your result.

[it_cowboy]

Going to try to check the knock sensor this weekend or next. Looks like ebay is the place to buy those for around $60. I'll definitely post back what fixes it. Maybe help someone else out one day. Please do the same with what you find out.

[it_cowboy]

I talked to a friend who is a nissan mechanic. He said the knock sensor can throw the SES light but rarely does. They often have cars in the shop with the code that will never clear but since they don't throw the SES they don't worry about it. He told me to check the O2 after the cat first.

[Bri4404]

Had the 0420 code and solved by replacing the forward o2 sensor. Replacing the rear o2 sensor first did not solve the problem.

[jamirokev]

Originally Posted by it_cowboy

Going to try to check the knock sensor this weekend or next. Looks like ebay is the place to buy those for around $60. I'll definitely post back what fixes it. Maybe help someone else out one day. Please do the same with what you find out.

I took my car in last Thursday and I got my car back on this past Tuesday. Turns out I had quite a bit wrong with my car. I dont have the bill in front of me but I think I remember the latter:

I needed:

New Knock Sensor
New Wiring for the Knock Sensor
New Cat
New New Exaust Pipe
New Head Gasket
Luckly my 02 sensors were still good

My mechanic went easy on me and only charged me for 4 hours of labor and this whole thing came to a Grand Total of : $1,238. Looks like Im eating Fast Food for a month now.....haha!

[naveed2126]

Damn.... a head gasket job alone can run you $1200 at Nissan. Even though that's a lot of money, good deal, considering they put in a new head gasket.

[jamirokev]

yeah a mechanic with sympathy is rather hard to find....