sil8ty

I thinking this may be something alot of Subarus may be experiencing and how many people do change the spark plugs since the expected lifetime of the plugs are very long. Iridium plugs may last longer as a metal, but it's not as good as an electrical conductor. I'm thinking it may have happened overtime, it's been close to 140000km. I'm running all stock on this car except GT brakes.

You guys missed it, the one I pulled out is at the top of this page,and also in this comment. It is what's considered too hot. It's not the engine, it's fine, no coolant problems. The spark plugs are running too hot (not the car) and can be noticed since it's totally too white. The above 3 spark plug pictures are proper spark plugs (copper though) of what you should get if you have proper timing/gaping. Iridium type plugs are what Subaru uses are harder to deform, but the one ones I pulled out were deformed because the gap has shortened. I believe that's the cause of my po0420 fault.

pictures of spark plug added, look back on top of page 2. I've included some pics of what your plugs should look like, if everything is OK

My cruise started blinking and the cel stayed lit when the p0420 tripped.

No, that's a drain, a flush should be done with a machine which circulates new coolant into the system while removing the old coolant at the same time. The major advantage is you should be able to monitor the old coolant till it's all be replaced and that it is free of contamination/sediment. Though there really shouldn't be any crap/rust in there.

No, I'm not saying the engine is overheating, the car is running leaner than normal causing a my cel p0420 fault, it's clear now, and I did do a coolant flush at the dealer recently too. Would have done the flush myself, but they say it's a flush, not just a drain and replace.

All of my spark plugs were running too hot, I guess the Passenger side was just worst. The higher heat also meant the car was running closer to lean. The plugs were from the factory and this was the first time they were changed. I'll add a picture later tonight And here they are, sorry I couldn't get a side shot, it's more obvious that the leads bent in because of the heat when compared to a new plug. I also realize I need a micro lens on my camera.

Hello, just thought I'd let people know I'm new here, but I've been struggling with this problem for a few months, replaced the o2 sensors already w/ Subaru parts, error still shows after abit of driving. After I changed the spark plugs, the error stopped coming back. Looking at the spark plugs I noticed that it was under alot of heat, it was all whitish colored. the Electrode also showed signs that the gap changed as compared to the new spark plugs. CAr was about 145,000Km, H6 outback 2005. problem showed around 142,000km. All good, 150,000km as of this post.