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2002 Subaru Outback L.L. Bean Edition H6-3.0
72 Posts
Discussion Starter #1
So every New Years I drive from Anchorage, AK, to Fairbanks (~360 miles one way). This year, while I was in Fairbanks my check engine light came on while driving (highway speeds for over 30 mins, was definitely warmed up), but I didn't panic. The next day I was going to drive home (~360 miles) so I stopped by O'Reilly's to get the code read and he said it was P0420, which was "Catalytic Converter Efficiency Below Threshold," but he said it was likely due to the colder weather. It was about 10F outside, while my car (which spent the first 12 years of its life in California) hadn't seen anything lower than probably 20F this year, but has seen lower in previous years without throwing a code.

Either way, he said my catalytic converter probably wasn't as hot as it wanted to be, therefore it turned the light on.

Anyway, I filled my tank at Carrs (Safeway) which uses Chevron gas with the recommended Supreme, and after about 30 minutes of highway driving home the light just shut off. Cool, right?

Well, now EVERYTIME I fill up which is either before work (cold car) or on my lunch (warm car), whenever I get on the highway after ~10 miles the check engine light comes on. I have always used the same two Chevron stations, always Supreme, never let my tank go below ~1/4 tank, etc., etc.

THEN, after about 24 hours the light will just shut off. Sometimes it's when I get in the car to go to work, sometimes it's mid-driving on the highway.

When I drove the car up from California in 2014 I had to have to fuel pump and filter replaced about a week after I got home when the car was around at 143,000 miles. I also had an O2 sensor replaced shortly after.

I know my car is 16 years old, but it's been cared for well, so I'd like your input on what it may be. I'm worried that when I go to get my next oil change in about 1700 miles or so the light won't be on, though, I suppose I can fill up right before I go in :roadtrip::iam:

On the Super Mod Squad
2002 Pair: 3.0 VDC Wag & 2.5 Limited Sedan
26,193 Posts
its happening from the particular drive cycle of that day.

I had it before in my own 2002 H4. and it would come on from the same trip out to the grocery store for me, (possibly with a trip to the gas pump). but on the same exact stretch of 2 lane coming back the p0420 would pop on.... I mean like on the same half mile of road, like 4 times.

a new rear o2 sensor, (= a Denso from rockauto, or amazon) cured that has not come back since.

such things get old / dirty/ wore out. (= this car has 115,000 on it now, replaced around 100,000, and maybe at 65,000 miles before that). no big deal.

incidentally. my H6 car has ALL the original sensors on it, with 125,000 miles on them or so, = steady diet of 93 octane since new.
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