Way back in 2011 I had a problem with my A4 coil throwing P0354 (Circuit fault) and P0304 (Misfire) codes. I replaced it and all was well.

Well, the problem has returned; but that's not much of a story...

At the moment the code only trips when it is exceedingly damp outside. We've had a string of warm winter days that creates a good deal of fog and generally damp conditions. That's when the problem manifests itself. When the weather clears up, so does the problem.

Oddly, too, is that it is always the same coil - A4 - causing the problem. I've checked the relevant wiring and connections, etc. for faults and never find anything. Maybe it is the cheap coils I'm buying!

I just noticed another odd thing. If you do a Forum search on P0354 you'll get 6 or so threads. In each of those threads, everyone has the same coil going bad - A4. What's with that?

 

I just noticed another odd thing. If you do a Forum search on P0354 you'll get 6 or so threads. In each of those threads, everyone has the same coil going bad - A4. What's with that?[/QUOTE]

That's because P0354 is ALWAYS about A4. Just as P0351 is A1, P0352 is A2, and P0353 is A3.

 

Could be a grounding issue or an ECM problem

 

Quite so. I thought P0354 was a code pointing to trouble in the larger coil circuit and P0304,5,6,etc. were pointing to a specific cylinder coil.

That being cleared up, what, as an example, is P0354 telling me and why must it always precede P0304?

 

It doesn't have to. Plenty get P0304 but no P0354.

Being P0 they're both generic so google will get you standard info or you can grab the free workshop manual and read Jaguar's stated known causes.

 

To check swap your #4 coil with another coil, clear the codes and see what comes up.

 

Each code in the series from P0300 (random misfire), to P0304 (misfire cylinder #4), and P0354 is for a primary or secondary ignition coil malfunction on cylinder #4. Each progression in the code sequence indicates a slightly different and decidedly more difficult and possibly more expensive problem to properly diagnose. From the basic random misfire to the more specific coil and or cylinder, etc.

All the module can really detect is that there's probability of such a problem not a certainty. You might also get some emissions codes as well if the misfire is severe enough or goes on for awhile.

 

Thanks for the explanation. I did get emissions codes and RP as things went along. I replaced the offending coil and all was well for an initial trip or two. We'll see what happens on the next foggy/damp day...

 

I was getting similar messages on my '99 XK8 but for cylinder #6 . Misfire, coil, emissions, the works. I bought four German/Spanish built coils for $94 on eBay and used one. So far so good as I've driven 200 +/- miles without a problem.