While driving my 05 max today my service engine light came on. At the stop light, I could also tell it was running a tab bit above normal RPM at idle. Nothing to drastic though. I took it to Auto Zone for the free diagnostic check to see what code they would be able to pull up. Below is what they printed out. I am trying to do a little trouble shooting before taking it straight to the shop. Any info will be greatly appreciated.

Trouble Code: P0420


Definition: CATALYST SYSTEM EFFICIENCY
BELOW THRESHOLD BANK 1

Probable Causes:
1) A/F RATIO CONCERN
2) AIR LEAK NEAR HO2S
3) IGNITION SYSTEM CONCERN
4) FAULTY CATALYTIC CONVERTER

 

What kinda gas you running ? I haul gas and sometimes a sriver might drop the wrong gas in the wrong tank, put a octane booster in and run in a lil hard.

Sent from the batcave

 

I just run regular. Not premium or anything. I will get the octane booster as you stated. Thanks for the reply.

 

Most likely your precat (I believe firewall side). Happens to just about everybody. I have that code as well.

 

Just to confuse you a little more, there could be several other things that can throw that code.

1. Bad O2 sensor - The computer compares values between the 2 O2 sensors, so 1 bad one can throw a code.

2. Faulty ignition coil - A misfiring cylinder will dump unburned fuel into your precat causing it to fail.

3. Vaccuum Leak - Will cause fuel air mix to be thrown off causing a rich mixture and, again, dump fuel into your precat causing it to fail prematurely.

Had 2 & 3 happen to my 01 Maxima.

 

Does anyone find it funny that DTC - P0420 has to do with smoke??