Jaguar S Type, late 2001, V6 3.0 litre petrol. MIL light comes on about 50 - 60 miles after reset and returns code P0420 - "Catalyst Systwem Efficiency Below Threshold Bank 1".

This started happening after all 3 ignition coils in Bank 1 had to be replaced (new spark plugs fitted throughout at the same time). Both Lambda sensors on Bank 1 have now also been replaced, but the fault light still comes back after 50 - 60 miles. I'm assuming that this is because the catalyst monitoring only comes into play after a certain amount of time following a reset?

I think there's also a slight loss of engine power when driving, but could not be sure about that. Checking the I/M Status shows everything as OK. I'm guessing that the catalytic converter needs replacing after it got contaminated during the failed ignition coil period - the MIL did flash a few times after the light came on for that fault, which I've read somewhere indicates that the situation is causing damage to the cat. I'd just like an expert opinion before going to the expense of replacing the cat. Thank you in anticipation.

 

Flashing MIL is a disaster, really does mean damage so probably is bad news, sadly.

You could watch the 2 downstream O2s waveforms. Suspect one will swing more or flatline.

Maybe better would be check temperature pre- & post-cat.

Could take the O2(s) out on the suspect side and peer in with a borescope.

DIY only if you have the tools & knowledge.

 

I had a similar problem with my Subaru Outback---it turned out to be the MAF sensor which was dirty.

If you check the"OBD Error Codes Explained for Jaguar"link,it suggests that a faulty Coolant Temperature Sensor may cause the error code you have described.

 

Is that the link with lots of wrong codes? Please use the proper jag codes PDF!!!!!

 

This is not a question of "wrong "codes.It is clear- P0420.The question is: what is causing the code to trip?There is nothing wrong with following the diagnostic procedure for the code using JTIS.
However ,as I found out with my Subaru,following the factory procedure did not resolve the problem.Just because I am curious--I checked the the link you look down upon and it sugested that a dirty MAF has been found to cause the code I had.So I cleaned my MAF and the problemis resolved.

Now in my post,#3,above I checked the link you look down upon,and it suggested that in addition to O2 sensors and defective catalysts,a defective Coolant Temperature sensor has been known to throw this code.

The cost of checking the CTS is insignificant,and is certainly less expensive than a new catalytic converter.

Perhaps you should "open your mind"a little,especially since the JTIS is the worst factory documentation for a vehicle I have ever worked with.

 

So far as i can see (even in the more recent files I have) Jaguar do not list that item as a possible cause for that code. Further, it is hard to see how a faulty ECT (aka CTS) can cause only one code, P0420, and that for a single bank on a V engine. I would hate to see someone head down the wrong route when fault-finding and suggest the ECT be left to the very very end of such fault-finding.

 

Yes of course--I assumed that the procedure JTIS Diagnostics suggested would be followed first.

As to how CTS(ECT) sensor can cause such a code,as I suggested earlier--open your mind--if you believe that both catalytic converters are operating at exactly the same efficiency then it cannot.(and if you believe this to be the case I have a piece of land in Florida I can sell you cheaply) but if the catalytic converter efficiencies are different then it is easy to see how it could happen.

 

What brand of coils were used? OEM or aftermarket - as the latter cause more issues down the line than OEM - as stated above - get this issue resolved quickly or you can plan on replacing that cat converter.

 

YOU HAVE A BAD(INEFFICIENT AS A % ALLOWED BY THE EPA) CAT FROM THE MISIFRES, AND IF YOU GO TO THIS WEBSITE AND GET THE ANGLED DOWNSTREAM 02 EXTENDERS YOU CAN FIX YOUR ISSUE FOR BOTH SIDES FOR $60
O2 Simulator, mini catalytic Converter cel fix
MAFS OR ECT CAUSING MAYBE IN A STREATCH, BUT P0420 IS THE FAULT, NOT THE CAUSE. MISFIRES ARE THE #1 CAUSE, THAT BEING FIXED THE DAMAGE WAS DONE. A FLASHING CEL IS FOR DAMAGE BEING DONE WHILE FLASHING, ITS SAYING 'HELLO HELLO LOOK AT ME! IM A PROBLEM!"

 

Thanks for all your feedback. New cat has now been fitted, and fuel consumption and performance are noticeably better. No sign of the light coming back - yet!!

 

Sorry, missed this. Not appropriate for UK as tailpipe tests are done here and would show any failed cat.

Stusjag - hopefully it's fixed!

 

Well tail pipe checks are very common in the US too and I would not pass in the Hoston area with out replacing the cat.
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Was the problem permanently resolved?

 

I have had the P0420 since I bought my S-Type 7 mos ago and have read some about it since then.. Several times I've read of these extenders being installed and passing emissions in California. I also read instances of after market cats being installed and the code returning where the extenders were then used. I have even read from one manufacture of cats that they may be needed with their cats if your code returns..

 

Hi guys , not been on for a while as i have had happy motoring since fixing the issues on my (then purchased) 2000 s-type V6 3.0,however reading these threads it seems i am not the only one having this recurring code P0420 on bank one. I have had a new cat fitted and a new sensor on the down stream, but not on the up stream, having chatted with a nice gent at the Jaguar Breakfast club, who happened to pass me his business card, he told me that "both" sensors have to be changed as confliction will occur throwing up the same code after a time.
I have yet to change said sensor so i can not say if this is true or not, has anyone else heard if this could cure the recurring code before i go out buying one to fit...?

 

From my limited experience, for a cat efficiency fault (P0420 or P0430), you want to change only the upstream sensor, but NOT the downstream sensor.

These codes, referring to catalyst efficiency, are determined by sampling "dirty" exhaust entering the cat, as measured upstream. The sensor sends out a reading and the PCM instantly adjusts the air/fuel ratio to compensate, constantly switching back and forth. The switching rate upstream (fast switching is basically good) is then compared to the switching rate downstream of the cat, where the switching rate should be slower to indicate the cat is cleaning the exhaust as designed. Since sensor switching tends to slow as they age, I tried a new upstream sensor on my '02 to increase the difference. I kept the old sensor downstream, as slower switching there is good, as far as the cat efficiency monitoring is concerned.

This took care of a marginal cat on my '02. Please note this is only applicable for a cat just slightly over the edge. It won't help with one that is severely damaged. I'm not sure why you're still getting such a fault with a new cat, but if you still have the old downstream sensor, reinstall that and install a new one upstream. That should help restore the required margin between the cat inlet and outlet, enough to satisfy the efficiency monitor.