My '07 XJR (90k miles) is showing a CEL, and DTC is P0420 "Bank 1 Cat Converter Below Efficiency Threshold"

I erased the code, but it comes back and flips on the CEL

Anyone else encountered this?

I searched the forum, and there are a couple threads about seafoam cleaning, etc, but only final resolution I read was to replace cat

Had a bad cat on my an 8 yr old Mercedes, and the dealer replaced it under (an EPA mandated?) 10 yr/100K mile emissions warranty. Does this maybe apply to our aging Jags?

 

Switch downstream O2 sensor from left to right respectively. If it follows the O2 sensor, you found the problem. If it returns after you swap left and right. you may look to cat itself. Dealer should honor if bad cat.

 

I suspect that the sensor is also part of the emissions system,
and hence covered under the emissions warranty. If that is the
case, I wouldn't be bothered with the knuckle bruising job of
swapping sensors around. I'd take it in and have them do
whatever was required.

 

Thanks Box and Plums!

Are the (downstream) O2 sensors a bear? I like the swap idea, as believe the jag dealer will otherwise fight to make this a "customer pay" job

Which is "Bank 1" (R or L)?

Are cats common failure item with these cars? (I'm new to X350 Jags)

 

Bank 1 is right side. Get an O2 sensor socket at local parts store. Takes only a couple of minutes to swap. If it follows O2, and sets P0430 after change, then replace sensors. If it still sets P0420, you can have a melted cat, oil or fuel contamination. Misfire or overheating can melt the cat. Never drive with misfire, as you are dumping raw unburned fuel into the cat, where it then ignites and melts it down. Use Denso brand O2's only, and they are less than $50 each for downstream, about $100 each for upstream online.

Dealer may or may not assist, as it will depend on the Service Manager.

 

Is it 10 yr/100k or 8yr/80k for a 2007 MY Jag.

 

Thanks Box

It was the RH cat in the only other forum thread I could find on P0420; perhaps susceptible?
I have an O2 socket, and will swap as you suggest
Have no misfire codes, etc, but this is a used car with unknown history. Seems to run well, and no oil consumption in the ~ 1500 miles home
Intake tube "dongle" was broken and leaking air downstream from the MAF, so fuel trim has been way off for some time. Maybe this was it, and caused a lean misfire

1 of 19: Do you see 8/80 emissions warranty for the '07? I have not researched...

 

yep sounds like rich mixture killed the cat (LOL)

 

https://www3.epa.gov/obd/pubs/420f15035.pdf

 

Thanks Box!

You're the man...

(I'm 1 year and 10k miles late, sigh)