For anyone who runs into these codes: after replacing the gas cap (dealer: $35) on my S-Type to see if that would resolve the evaporative system leak, I replaced the purge valve canister ($105 from dealer) and this completely resolved the issue.

When I left the engine idling for a few minutes there was a clear continuous clicking sound every two minutes or so coming from the original purge valve canister, leading me to suspect it may have failed. I replaced the purge valve canister, reset the DTC codes, left the car idling for 5 minutes, drove for 20 minutes at 80kmh, giving the car enough time to run the Evaporative System test. The fix was confirmed resolved once I saw the Evaporative System test had been run successfully (on my code reader).

Annoyingly, I had taken the car into my local Jaguar dealer months earlier and they had (I later discovered) somehow misinterpreted the P0442 code as a "misfire" problem and replaced a whack of parts to try to fix a non-existent misfire problem for $1500 without even attempting to address the evap issues (they only attempt to fix the first code they pull in case that is the cause of the others) - so I ultimately decided to give it a go on my own to see if I could do better...

The purge valve canister replacement is extremely easy: two bolts and three clip-on pipes, and the part is easily accessible under the hood on the driver side. This may not be your resolution but check for clicking coming from the purge valve canister over a period of 10 minutes if you get these codes (or even just P0456 alone).

This post has the part #, pictures and steps to replace the part:
https://www.jaguarforums.com/forum/s...-really-45876/
... Though his symptoms were a bit different, it's the same fix.

Hope this saves someone some time and/or money...

 

Thanks- I'm battling this on my own car. A new gas cap made no difference and a smoke test found nothing.

 

Mikey, in my case the purge valve was obviously clicking. I've read that in other cases the purge valve developed small cracks which can leak and which are usually not detectable by a smoke test.
I was going to head to the gas tank seals next and then the charcoal canisters if the purge valve replacement didn't work.

 

I hope you get your money back!

 

Sadly, Walmart does not sell Jaguar gas caps.

 

I meant his $1500!

Oh... this is an "oil", er, joke...

 

Oil is never a joking matter.

Precautionary pancake bunny:

 

The first time my ECL came on it read P0442, cleared it and a few days later the ECL came back on and now I get P0456. I will check the purge valve canister first. What else should check?

 

Every item listed in the known causes column for each code, in the Jaguar codes PDF / JTIS - both free downloads. Probably already in this thread, but incomplete.