Po 420

[cookie]

Just a follow up in case it healps anybody else. A few years back I got a PO 420 code on my California 99 Forester. I think it had about 125,000 miles on it then. A couple of places told me I needed new cats at big bucks.

I fitted a new front oxegen sensor and the code went away until a few weeks back at about 147,000 miles. I figured it was the front sensor again and ordered the wrong one from a place I could not take it back to. CA and 49 state are different.

At that point as soon as I shut off the warning light it would come back in just a few miles.

Then I remembered when I bought the front sensor I had also bought the back and not fitted it to see how long it would last.

I put that on and the car has been cured for several weeks.

The lesson seems to be to change the ox sensors before the big bucks cats (over a grand quotes), and the rear can last a couple of years longer than the front.

Oh, and by the way don't order an oxy sensor with out the serial number from anybody who won't take it back.

[fleming442]

Good luck with that. I thought I was being cool and had my CEL out for the same reason..... If you do a little research, the light will come back on after a proper "drive cycle" ( as cited in the FSM). I usually drive above 80mph, so it hasn't registered as a drive cycle yet. If I get stuck behind some slowpoke for 20min., the CEL will trigger. I'm holding out for new cats as long as I can extinguish the light and pass MD's emmision test.

[Cougar]

When it comes to deciding if a CAT is really bad I think it is wise to look at the signals of the front and rear sensors using a scope or scanner to see what is really going on.

[cookie]

I think Cougar is right, if the equipment was available it would be best to check.

I would think it would have come back on if it was going to, it's a thousand miles now and today I drove it on the freeway to SF twice, that's about 55 miles, slow though SF traffic twice (a lot of lights on 19th ave at rush hour), a trip down to lunch, a couple of miles, and San Bruno, maybe fifteen miles of traffic and lights.

I'll be disappointed if it comes back on but I have gotten three years more out of it, and it does look like I may make more yet.

I think this total repair has been about $150 which fits my pocketbook better.

[Olnick]

Off topic, but hey, cookie--nice to see your handle on a thread!

[cookie]

Nice to see you are still a Subie owner Olnick.

 

When I first got the old 99 I was on here all the time to figure out how to fix her up. She's been running without a glitch other than a transmission rebuild and a little service for a few years now.

[Hondasucks]

There is a bulletin on these, more of an online training module, that we all had to do, mainly for warranty stuff, but it covered plugging in the laptop, driving the car over 50MPH for two minutes and then backing out of the throttle and watching what the AFR and O2S (Air-Fuel Ratio [front sensor] and Oxygen Sensor [rear sensor]) are doing, since a faulty sensor CAN trigger a P0420, although more often than not if you have a P0420, you've got a cat on it's way out. Also, don't be tempted to get an aftermarket cat, my dad's Outback has an aftermarket cat on it (previous owner) and when I did the head gaskets on it, it had a P0420

[cookie]

I do suspect the cat is slowly on its way out but so is everything else as she nears 150,000 miles. I have to keep an eye on the oil but as long as it goes though smog I might get a few more years out of the car.