OBD II code 0420

[DannyP]

Bought a BK '98 GT wagon a year ago, been skulking here.

 

Thanks for the heater control fix!(Used RS bulbs)

 

Changed timing belt, stopped oil leaks, changed clutch(and rear main)

 

Need help, have had a recurring P0420 code, which is too much ox in the exhaust at second o2 sensor. So with almost 130 K on the clock, I changed the rear o2, and after 3 engine "emission" cycles, light came right back on. I used to get a couple of weeks before the light came on. I have checked for intake and exhaust leaks and am wondering if anyone has found a cure for this that I cannot. Inspection due (including check engine light!) by the end of November. I have an Equus 3100, so no problem to reset or get codes.

 

Thanks for a great forum, as far as info and procedures, along with a couple laughs!

[andrew.anderson]

I have no idea about your code but would like to see a picture of your car when you get the opportunity to post it.

[autotech]

p0420 codes are typically Cat converters. They are on hondas that i work on and i think its pretty common throughout the auto industry.

[subarupartsdude]

^ That's correct........cat conv needs to be replaced.

[rougeben83]

^ That's correct........cat conv needs to be replaced.

 

 

Not necessarily; more likely it's the rear 02 sensor that's gone bad (ie the sensor that's supposed to detect if your cat is bad).

[19Outback95]

Not necessarily; more likely it's the rear 02 sensor that's gone bad (ie the sensor that's supposed to detect if your cat is bad).

 

thats what ive been told.

[autotech]

well replacing the rear sensor is way easier and less expensive to change anyway...

[DannyP]

I changed the rear sensor. Still after a few days or a week, it comes back on. Car must do three emission cycles before it looks at O2 efficiency again. Also bought a OBDpros interface for my laptop. Having a problem staying in communication with the Suby computer. Was trying to get idle and underway voltages to O2 sensors, which will determine if it really is the Cat at fault. After spending $100 for the tool, I probably should have just bought a CAT and reset the code.

 

Too bad a reflash to make the ECU less sensitive isn't available!

[autotech]

cat would be my bet as i stated before, but i dont know the older subarus as much as i do the newer ones. I never had a CEL on my 92 SS, so i was never given the pleasure of researching.

[PeterJMC]

I don't know anything about that error code but it wouldn't hurt to try cleaning the MAF sensor. Maybe it's not measuring air correctly??

 

Use some electronics cleaner and VERY VERY lightly rub the sensor with a lint free cloth.

[oncesir]

The P0420 code is Catalyst Efficiency Below Threshold. You need a cat or search the web for spark plug anti-fouler. This $3 part will fix your p0420 complaint. hth

[dplacen]

P0420 It needs a cat very common on subies. I change them at work all the time. that will solve your problem.

[DannyP]

Well sorry but I fixed it and it wasn't what you thought. A couple weeks ago the exhaust went from whisper quiet to really loud one morning. I checked it that night and changed the right side header gasket, as that's where I felt the leak on my hand. Still loud so I figured it was leaking from the pipe. I ripped off the heat shield and there it was, a hole where the two pipes y together about 4 inches off the head. I dropped the exhaust, disconnected the battery, and Mig'd it closed. Problem solved, I hope. It's been about 10-14 days and still good.

 

It makes sense to me that the O2 sensor was not reading what the computer thought as all the exhaust wasn't going by either sensor. Oh well, $60 for a sensor and nobody's labor except my own I can live with!