Got a CEL today that is PO420.

 

Catalyst system efficieny for Bank #1 is below threshhold for the current operating conditions. (Bank 1 identifies the location of cylinder #1, while bank #2 identifies the cylinders on the opposite bank.)

 

Plud wires are 2 months old, fuel filter is 2 weeks old, plugs have 8000 miles on them, engine has 5500 miles on it.

 

any ideas??

 

Thanks, Mike

Do you have 3 or 4 wires coming out of the O2 sensors? If its a three wire O2 sensor, try grounging the body of the O2 sensor to the body. A hose clamp to hold the bare wire on the sensor works. Take the other end to the ground just behind the front strut.

 

If you can find someone to read out the sensors, you can see the response from each sensor. New Sensors may fix the problem also. Search the board for O2 sensors and you will find may posts.

Thanks for the reply,

 

The sensors have maybe 5000 miles. The front I believe is a 3 wire and the rear is 4. Stock replacements.

I switched them when I went to a borla header and stromung exhaust.

 

What is with the ground?

Got a CEL today that is PO420.

 

Does this mean your car is stoned?

p0420 may be bank 1 sensor 2 which applies to the sensor after the catalytic converters. mine was throwing that code when i changed the exhaust and took out the cats. sensor is probably faulty.

 

good Luck

 

Joe

Do test the O2 sensor before replacing it, seeing as it's so young.

 

The "cat efficiency below threshold" code can also be caused by an exhaust leak anywhere between the engine and the rear O2 sensor. Make sure yours is sealed up tight.

 

Did you switch to a more freely-flowing cat when you went to the Strömung exhaust? Maybe the ECU is still calculating based on the stock cat.

 

Just a couple of thoughts.

Sorry i did not see wher you had replaced your exhuast. try this and then reset. get a 19mm spark plug defouler and drill a 1/2" hole though it. then grab another one and screw it on the drilled end. then take out your o2 sensor and install the defoulers. then put your 02 sensor back on. this worked for me until i got Em.

 

 

good luck.

 

Joe

thats the usual code that comes up on my impreza. i just clear it and keep driving. it only pops up in severe bad weather for some reason.i know the cat isnt dead on the car cause when i ran a gas analizer, it was putting out clean air, well, at least cleaner than the air in the shop i was in. i am thinking that hte o2 sensor geeks out in heavy rains, at least on my car.

last New Years I got the code in a rain that was fierce. Cleared it and no return. I think the rain cools the cat below the optimum temp.

I have recieved this on a 96 Outback as well. 2.2 engine Manual transmission

 

With all this rain in the Northeast I wonder if it could be from the rain as was mentioned.

 

Either way I am planning on changing the sensor. I have a couple of questions.

 

1. Any suggestions on getting a replacement, Cost and supplier

 

2. How do I clear the code after replacing. I do not have a reader. (It was diagnoized by a dealer and at autozone)

 

Thanks for any help

 

Scott

1996 Outback 182,000 miles

I'd actually recommend AutoZone. Get a Bosch (is OE) sensor from them if they have it in stock, and borrow their O2 sensor wrench for free. Then take it back to them and have them clear the code.

I thought I could use a normal wrench. This needs a special wrench to remove ??

 

Also not sure what you mean by OE. Maybe you meant OEM ??? I also thought Subaru used NGK parts.

 

Thanks

 

Scott

 

I'd actually recommend AutoZone. Get a Bosch (is OE) sensor from them if they have it in stock, and borrow their O2 sensor wrench for free. Then take it back to them and have them clear the code.