I've been trying to diagnose this persistent P0420 code for a while now. From my thread here: https://www.jaguarforums.com/forum/f...-p0420-235647/ I'm pretty sure the cats were bad.

But something else I've noticed that's peculiar...it may be related, maybe not. I was on the VAP Stage 1 tune via ECU flash. Thinking I'll have to take it to the dealer, I flashed it back to original. Strangely, after every flash, the P0420 code triggers. It doesn't matter what map I flash, it seems like the very act of flashing triggers the P0420. Anyone else have this happen, when trying to flash the ECU triggers a CEL?

 

I'm sure that flashing the tune on triggers the CEL and several error codes, this has happened to me all four or five times I have flashed and many others have also reported this. After a few drive cycles they disappear and don't return but I clear them all straight away using my iCarsoft LR 2.0.
The same thing will be happening to you with the exception of the P0420 code which for you is a "real" code.

 

Good to know, thanks. When I asked VAP they said they had no idea, as in they never heard of it before...I just find it peculiar and maybe a little more than coincidental that it always triggers the same code that's making me lose sleep over.

 

Agree with OZ, in that when you write to the ECU while the car is not running normally (i.e. when you flash/ upload the tune file) it will almost always generate a CEL, that should clear after a few cycles/starts. It will usually be related to communications/gateway/canbus, but can vary.

As long as the CEL is not on persistently (i.e. when you are not flashing or just flashed), it is likely not a "real" issue.

If you get that code under normal circumstances while just driving, then you likely have an issue. And of course, true Cat failure will typically result in a flashing CEL, and you should stop the car as soon as it is s safe to do so in that situation.

DC

 

Every time I flashed a VAP tune the CEL light comes on. Never checked the codes being thrown. However after exactly five restarts it always goes away.

 

Just learned something new again 👍

 

Interesting. I've never had a CEL from a reflash.

 

Same here.

 

I have usually had a CEL after flashing but I clear it with my fault code reader as I'm too impatient to wait five drive cycles...

 

It's not actually 5 drive cycles, it's just 5 engine starts back-to-back..

 

You’re probably right Stuart, I told you I was too impatient to verify 😂