2003 Murano SES Light - Code P0420 P0340 - My experience
I have recently experienced the dreaded P0420 code along with some other ones and wanted to share it with you - you draw your own conclusions on what to do.
The P0420 code came on about a month ago.
The SES light went on, and not knowing what to do, I went to Autozone, who hooked up the computer and let me know. They also told me that I have another code, the P0340 - camshaft sensor fail on bank 1. I wondered if that was coincidental.
Started my research. Came on this fine forum and did a bunch of checks on what the code is, etc.
This is when I realized that this code indicates need to replace the cat on bank 1 (near firewall). Prices ranged greatly from about 800 through more than 2K.
I went to a local muffler shop to get a quote, and was quoted about 1K in work. I asked what the problem is and what is the best cheapest solution.
I was immediately told (after they hooked up the pc and checked) - yes, it is the cat and you need to get this done before it ruins your engine.
On this forum, i various shops, everybody, as soon as they saw the P0420 code, told me the cat needs to go. I got ready spend the $ (there are many other things I can spend that much money on, with wife and 3 kids, never mind the damn dog).
Before taking the car in, I ordered another camshaft sensor to replace.
Did more research on the P0420 on other forums too.
After about 3 hours of searching (yeah, when I get something in my head, I don't let go), I stumbled on a mechanic forum where they were discussing nissans.
Upon searching the P0420, I saw posts by a mechanic who said that the P040 may mean the cat change, but that many people have this code mis-diagnosed often at shops. He said many shops jump at the replacement upon seeing the code (that is when they stop diagnose, after they see the code).
He also said something else. He said, that the P0420 code almost never appears all by itself. There are other codes present with it.
Furthermore, he said, that to be sure, you should resolve all other codes before knowing the cat is in need of replacement, reset by pulling battery and driving for 100 miles.
So when the sensor arrived, i was getting ready to test his theory.
Had 2 codes, the P0420 (replace bank 1 cat) and the P0340 (bad camshaft sensor on bank 1).
Plugged the new sensor in and it immediately resolved the symptomatic hard starting went away.
Then, to make sure I follow the mechanic's instructions, I disconnected the battery for 10 minutes. Then after reconnecting, I took the car for a drive on a 100 mile ride.
Sure enough, after just over 100 miles, I looked down and the SES light was gone.
I was real happy with the result. Bottom line, if you get the code, make sure you resolve any other codes that appear with it, or you may be spending money that you do not need to get the code taken care of.