I recently bought at 2009 Jaguar XF Supercharged from a small local independent dealership. Shortly after the check engine light came on. P0420 and P0430 Catalyst inefficiency errors. I have an appointment at the Jaguar dealer for Saturday am.

New MAF sensors, air filter, upstream o2 sensors testing good at 3ohms pulled out of car and tested with multimeter. Downstream o2 sensors are swinging widely from .2 to .8 or just under 1 volt. My scanner doesn't show upstream sensor voltage, but the downstream voltage looks like what you would typically see for an upstream o2. The car has 34,000 original miles. Carfax says throttle body was replaced at 28k. I have 2 questions:

1. What are the chances that both cats fail at relatively the same time?
2. What are the chances that the Jag dealer replaces them under fed emissions warranty.

Have about 4 months left until it's 8 years old.

Thanks,

 

Cats are covered by an 8 year 80,000 mi Federal emissions warranty→https://www3.epa.gov/otaq/about/faq.htm
better get it to a Jag dealer fast. If the cats have failed by no fault of yours Jags got to replace them.

 

The loophole is if the cats have been damaged by a faulty O2 sensor then all bets are off. Friend of mine had an LR2 with this diagnosis and the warranty was voided. Sadly this ethanol adulterated excuse for gas is often the cause of O2 sensor issues where they get coated and don't respond in a timely manner. The ECU compensates by going rich and that's what kills the cat. I would gladly pay for the choice of just gas gas please. But that's not an option here in Texas.

 

I believe the upstreams are current-sensing devices (different internal technology) so you can't really look at the voltage. OBD tools should show what they're reading.

 

Yes it's possible. You have a used car and the guy before you might have been driving around with a rich code for months and then got it fixed. But mean while the cats have been torched trying to get all the excessive fuel burned up.

But we just don't know the history. Try to get the factory to replace both cats if possible,

No Ethanol does NOT cause O2 sensor problems. I am in Texas and my 2005 STR has 3 or 4 original O2 sensors. I have 125K miles on the car. ALL Ethanol based fuel.

Look elsewhere for your problem but my bet is it was caused before you bought it. In fact it may have been the reason the previous guy sold the car?
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I had to have O2 sensors replaced on a three year old Subaru with 30K miles and the shop attributed this to ethanol in the gas. They said they had noticed an increase in "failing" sensors in that they still work but don't respond to the ECU in a timely manner. Maybe Jag fit a different O2 sensor.

Doesn't take away from my desire to drive with gas that isn't adulterated with cr*p that has no business being there ;-)

 

So I made an appointment at the dealer and about 20 minutes after I get an appointment scheduled, I get a new code. P0131 - O2 Sensor Circuit Low Voltage Bank 1 Sensor 1. So I let the thing cool, swap upstream sensors. The next day I get P0151 O2 Sensor Circuit Low Voltage Bank 2 Sensor 1. So the code followed the sensor.

Hoping this is an o2/AF sensor/cat problem and not a system wide problem before the exhaust. My code reader won't read AF sensor voltage, only mA's so I'm not sure how to tell if it truly is the AF sensors without replacing them.

My question is, why would both cats show inefficient codes, if (presumably) only one upstream AF sensor is bad? Perhaps both upstream AF sensors are bad and one is just too bashful to speak up?

 

Your theory is plausible. Carfax shows new throttle body at 28k. So perhaps there was a throttle body issue that torched the cats. Speculation, but certainly possible.

 

Apologies, I'm not finding a sig line in member dashboard. Is that the same as visitor message?

 

It's somewhere in the User CP. It's years since I set mine so can't recall where.

mA is what you could use for the upstreams I expect but generally the codes are very accurate. (The PCM seems hardly ever to fail.)

We have ethanol here, too, and at 127K miles I've had to change just one O2 sensor (an upstream).

 

You said you've swapped the O2 sensors, so you've physically seen the cats fitted to the car, are they original?

P0420 & P0430 are also tripped at the same time if you fit aftermarket "sport" catalysts with a low cell count... maybe the previous owner changed the cats? or maybe he knocked the bricks out of them?

Or maybe they are just both stuffed... You really need to pull them off and have a look inside.

 

Thanks Cambo. I agree. They are original. At least they are Jaguar parts and look like the original. Certain they are not aftermarket. I agree with you I'm gonna have to pull one and see what's up. At this point I'm confident that the cats are bad, I'm just concerned about why. More specifically, if there is a condition that will ruin new ones if I replace. The car runs fine, just the CEL and the codes.




You can partially see the Jaguar badge

 

If the fuel trims are OK then new cats should be OK.

Try a borescope via O2 holes.

 

Here are the Realtime fuel trims at idle and 2500 RPM. They look normal to me. Any takers on a second opinion?