p0421 code - Jeep Wrangler Forum

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Old 05-13-2011, 10:49 PM   #1
jrussblues's Avatar
Join Date: Apr 2011
Location: se la
Posts: 3,093
p0421 code

So I've searched on this and it says that the reading on bank 1 post cat is bad.

I replaced the o2 sensor and plugs. The only other thing I can think of is the mini cat...which should be under warranty for 2k more miles.

Is it possible or probable that because I just started running 33s on 3.73s that the engine is running too lean causing a bad reading?

Just want to exhaust all options before taking it to the stealership.


06 LJ
78? CJ-7
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Old 05-14-2011, 12:42 AM   #2
rbloodhound's Avatar
Join Date: Mar 2010
Location: Crowville Louisiana
Posts: 451
I was getting that code on my 05. I finally tok it to the dealer. Both front o2 sensors were bad. Pre cat.

I have since had all cats changed under the 8 year 80k emission warranty.

This has all Ben over the last 3 weeks.
05 TJ unlimited, Slightly Modified
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