So I've had a check engine light on my X-Type since I bought it in March 2021, it was basically a P1000 that wouldn't clear because of some strange EGR fault, but the car always ran fine.

Every year when I take my car to do the NCT (Irish MOT) I've always had to clear the fault with my scanner just before I hand the car over for the test, and then the MIL will be got for 3 restarts and it will pass the NCT, and the light usually comes back on on the way home.
So today I had my NCT and I hopped into the car to drive there and saw that the check engine light didn't come on. I had to do a double take because it was there every day for the last 3 and a half years!
When I got to the test centre I checked with my hand scanner and the P1000 was completely gone.. I was very confused, and a little bit suspicious.

But the car passed no problem, and the MIL or the P1000 have not returned. (Although I do now have a P1664 so I might just need to clean the injectors).

Does this make sense to anyone?
I didn't do anything out of the ordinary before the test, just checked the fluids, gave the car a wash, topped up the oil a with maybe 100ml of oil, and gave the car a quick hoover.
And put the splash shield back on after changing the oil a few weeks ago.

It seems like the problem was always something to do with the EGR not completing the system monitor readiness test, even though I replaced the EGR a year or two ago, and I've done a lot of fiddling with the car before and after this, but nothing ever made the MIL go away.

Of course I'm quite happy about it, but still curious to know why the light went away by itself after all this time..

 

P1000 is not a fault. A forum/site search will show what it is, with details.

 

That is pretty strange but I can tell you that just about the exact same thing happened to me with my 2006 S Type. The light had been on since shortly after my last inspection and miraculously just went off prior to my next inspection. Nothing at all had been done to the car except a wash inside and out. I never scanned for codes since as you said the car was running just fine. It has now been a month and the check engine light has not come back on. I am also happy but also curious as to how this would happen.

 

Yea, the only explanation I can think of is that maybe I bumped a sensor when washing the car, because I did do a few quick sprays on the underside with the power hose. But still, if a sensor was that "twitchy" then I think the check engine light would have been going on and off randomly over the last few years as I went over bumps, and through puddles, and when doing work on the car.
Or it might be a bit of random goop on a sensor that just happened to fall off at the right time.

Then again, the light might come back on in a few days and I might be back to square one!