I'm a new member here and new Jag owner as of a few weeks. So far I've been able to get great info from this site to help me with a bunch of odds and ends.

So my X type CEL is on now and the code reads P0420 --- what does the group say I should ? The car runs great, no smoke, no shake, no hesitation ... so now I'm trying to find out what I should be looking for ? Should I keep driving it as usual ?

Anyone have some suggestions ? I've checked and googled around but figured I would put this out here and see what other feelings are of the group.

02 X-type 2.5 auto.

 

I would say to have a computer connected up to the car and see if you are simply getting low efficiency out of the cat or if you have a problem with the downstream O2 sensor. The other thing that may do something or not is to run a can of Seafoam through the intake (if you need directions, let me know, pretty easy to do). That will help clean out the cat some and may make your situation better. Granted, it may also do nothing other than create a bunch of smoke.

 

Thanks - I need to find a place that can hook the car up to a computer and give me an honest diagnosis instead of - 'yeah you need new catalytic convertors' after simpy plugging into the obd port. I'm hoping it's just a bad downstream sensor and easy ( aka cheap ) fix. I just hate to buy a new sensor and then it still has the CEL.

I was also thinking of running cataclean through it, but have heard mixed results.

 

Decided I would pick up my own scanner last night and went with a Harbor Freight 60693 Deluxe ( OBD II Scanner - CAN & OBD II Deluxe Scan Tool ). It's not the professional series, but it's better a basic reader. Also with the 25% coupon it wasn't too bad a deal.

Checked codes again and still had just the one P0420 and a pending P1000. Cleared both and will see if the CEL returns. Really not sure how to use all the other functions on the machine yet - will need to play with it some more.

 

myexcursion, what you need to look for is a setting that talks about either the Bank 1 upstream O2 sensor voltage, Bank 1 A/F voltage, or Bank 1/Sensor 1 voltage. These are all talking about the same thing. You want voltage to compare to the other upstream sensor. If the voltages are pretty much the same, then odds are you are looking at a cat replacement. You can also check the downstream sensors to make sure, but odds are, since you don't have an O2 sensor code, that is not going to tell you much that will be definitive.

 

Looking at the same code now (plus a 430); my indie's tech said "bad cats, always is a bad cats with those code...". Unsurprisingly, he works full time for a dealership (not Jag).


Hmmm, I've been turning wrenches for 40 years now...I've seen maybe 6 bad cats in my life, and 4 of those were caused by leaded gas!


Using resources from here, started checking sensors. very slowly changing reading on ups, downs dancing around like a disco.


Both upstreams had blown fuses. New fuses, now both are rising from about .25 volts to about .8 volts every two seconds or so.


Downstreams are still dancing, but the 430 is gone, and that sensor is at least dancing within spec. The other is still bad.


While it could mean a bad cat, I'm perfectly willing to wager that changing the downstream sensor will fix the problem.


My question: who has replaced their downstream O2 sensors, and what brand/model did you use?

 

I'm still needing to figure out how to use my scanner. I picked up a scanner from Harbor Freight ( OBD II Scanner - CAN & OBD II Deluxe Scan Tool ), but not sure how to use that particular model to check the O2's. Hopefully will get to search the interwebs and find some step by step.

Also -- what 'fuse' did you change on the upstreams ? I didn't know they had any, where are they ?

 

F38 and F42 are green 30 Amp fuses in the underhood fuse box...and they aren't marked! However, F29 and 33 are, they are on the outside row, 38 and 42 are right next to them in the middle row between the outer row of fuses and the relays.

They were the only two blown out under the hood, and they sorted the upstream sensors right out! Apparently, they had been a problem before, since they had the blown fuse indicator fuses in both. Gotta tell you, bright red LEDs make it easy to spot the blown ones!

My gauge is a bit more intense than the garden-variety readers; I can monitor a number of functions in real time...although the car does NOT like to be driven with it connected! (older UltraGauge). No the best reader out there for the Jag, but it has saved me a few dollars so far.

 

I think these are the fuses being talked about.

 

They would be the ones!

 

Thanks Panama & Wa3ra ! I'm going to take a look in the morning.

 

checked both fuses and they were fine -- so back to square one.

I did figure out how to gather live data from the scanner though. Now I need to know what I'm looking at/for. I'm assuming I need to perform the data log after the engine has warmed up and is in closed loop. In order to check the o2 sensors - should I gather the data log at idle without increasing rpm's ? What am I looking for ?

Hope it's just a lazy o2 sensor causing the p420, but not feeling so confident it's an o2 since I have no other codes except for the 420 code, but worth a shot.

Next step if this does not pan out is trying to figure out the easiest way to see if there is an intake leak somewhere.

 

I "borrowed" this from another Q&A site.

The ratio of fuel to air in the combustion chamber is identified with the Greek letter 'lambda' hence the term 'lambda sensor' as the name given to the O2 sensors used in vehicles. Ideal combustion of gasoline occurs when the fuel : air ratio is 14.7:1 (fuel is 6.8% of the mass of the mixture) at this point the lambda value of 1.0 is assumed. As the lambda value drops the fuel:air mixture is becoming richer (less air more fuel) and conversely as the value rises the mixture is becoming weaker (more air to fuel).

With the engine up-to normal working temperature, check the output of the sensor wire, normally black with Zirconia sensors, you should expect an output of 0.2 – 0.8 volts fluctuating between these reading approximately 2 – 3 times per second. If the output voltage is lower than this, i.e. 0 – 0.2 volts there will be a lean running or excess oxygen problem. If the voltage is higher than this, i.e. 0.8 – 1.2 volts then there will be a rich running or excess fuel fault.

End of "borrowed" data.

I believe that the voltage change should be observed in the UPSTREAM sensor while the downstream sensor should be relatively constant for a CAT that is working properly. There are several real-time scanners that can give you this info while the vehicle is running.

Link included - http://www.bluejag.co.uk/o2sensors.php