Hello Jaguar fans,
My English 2001 XJR has been reporting the 0430 fault code.
Looking back over its service history, at 106k miles, and 125k miles, it showed this fault code. History says definition is CAT SYSTEM BANK2 BELOW THRESHHOLD.

I got the car at 145k miles. It's now thrown up the same code. I can change the o2 sensor, it's the upper left hand side. But, will this cure the fault? Or is it likely to be something else, causing the o2 sensor signal to report this?

Anyone know of a definite cause/fix would ensure a drink on me!

The car is the best I have ever owned, and is being lovingly brought back to her former glory. I'm working front to back overhauling the bushes, underside paintwork, and any mechanical details as and when I get the time. It's booked if for paint (stone chips) in the spring. The wheels are being shipped back to BBS in Germany for overhaul too. I want it mint, it warrants it!

Happy motoring
________
GB500

 

If the O2s haven't been changed yet, it's almost certainly the post cat O2 - pretty sure Bank 2 is drivers side but I could be wrong. At over 145k, it's definitely time to replace. This isn't 100% sure - I mean, it *could* actually be the cat, but a failing O2 is much more likely.

Also, now would be a good time (if finances permit) to change out all of your O2 sensors. You'll notice slightly better performance and mileage, and it's really not that hard to do.

 

The best way(only way) to properly diagnose the cat is with data monitoring of the pre and post cat o2 sensors. It would be difficult for a bad o2 sensor to mimic the exact requirements to flag the p0430 code but watching the o2 sensor reactions in a live datastream will tell you if the cat is the problem or not.

 

I had this problem, the upstream O2 sensors were at fault. the downstream sensors only signal the PO430 code. This was also verified by the tests in Alldata. When scanned these sensors were flatlining. Any car with these miles is going to have sensors that are far from optimum. Your fuel mileage and driveability should improve with new sensors. I am not sure the UK V8s have four sensors, but if there are only two, I would replace them.

 

while 02's are like spark plugs and do degrade with time, cats faults are cat faults, and I continously have to tell other techs to quit making diag difficult. We have 3 cars in the shop with replaced 02's that still kick cat codes.......the good news, like Volvos, Jags have tight thresholds and run fine with cat codes kicking out, so its up to you if you want to replace expensive cats.....but thats the inevitable

 

^But, the only way the ECU can tell if a cat is bad is from O2 sensor readings, no? So if an O2 is failing, you could have a false failed cat reading. Theoretically, sure, it should throw a failing O2 code, but I've seen BMWs fail to throw them and give cat codes that were fully caused by O2s. Just my $.02.

 

yes, but I guess I should ellaborate. We have to FRED 02 sensors Jags way of making us jump through flaming hoops an run dataloogs and email to jaguar before they will approve 02's for replacement, for vitually no time to do all this. Reason, a large majority of 02's that test fine no fault found when return to the manufacturer. ie techs throwing 02s at cat faults, when the cat has degraded. But like emmissions testing and requirments, the thresholds are tight, cats used to be replaced only when they melted or broke apart inside. Cat codes are another reason to fix misfires quickly at not leave them, they poison the cats and knock the efficiency down to ck engine light levels. Of some of the things Ive done to either stop or prolong 420/430 codes are to flush injectors and clean intake track. I consider this a maintence item every 60k miles, and since Ive sometimes gotten the engines efficiency back up the cats work better too. Kinda like being diabetic, you keep over loading your body with sugars and starches you overwork your pancrease and can lead to burnout Type I or poor effeciency TypeII. But with proper diet and exercise you can increase the effeciency and many times stay type II, but other moves right ahead into type I....just a familiar analogy

 

Only the down stream, post catalyst o2 sensor is used in testing catalyst efficiency and a failing o2 sensor in this position WILL NOT set an efficiency code. It's very simple really and i agree with brutal in this regard. Why are you trying to make things more difficult than they really are. The only thing coming out of the catalyst if it is working properly is CO2 and water vapor with a tiny amount of CO. When the down stream o2 sensor detects the presence of oxygen in the exhaust stream the efficiency code is set, it's that simple. I have never, ever seen an o2 sensor fail and cause a false reading of oxygen when none is present. They nearly always fail(minus heater failures) either flatline low or open circuit.

 

Thanks for the replies. Seems there's a bit of a grey area around changing them then?

The upshot as far as I can gather, is
1. it's better to change now.

2. Jaguar have tight thresholds for emissions, so there's a possibility that it won't cure it.

3. English, (at least '01 XJR's) have pre and post O2 sensors, so all four will be changed.

But only if it starts doing it regularly - it did it when I came off a long, fast run and hit crawling traffic. I've cleaned the induction/TB. And will do an injector clear-out, see if this helps.

For now, I'll see if it throws it up again, and do a live monitor of the sensors.

Paramount the Jag tuning specialist have just released big bore cats to fit to their stainless exhaust system, which my car has, I think a pair of these are on the shopping list now too.

Otherwise, it's doing great, pulls like an Airbus on take off. Fitted new Michelin Pilot Sports yesterday, great rubber, but very expensive :-(

All the Best!
________
medical marijuana doctor

 

Your latest description does sound like the catalyst is failing. The fact that the code was set after hitting slower traffic leans to the catalyst. When you are at high speed the catalyst is running hotter and is in its most efficient mode, when you slow down the cat cools and becomes less efficient and is probably dropping below the threshold for the p0430 code.