A while back, I got the CEL, read the codes. Only the P0133 showed up. Whent through the FSM procedure, ends with "replace O2 sensor".

 

[edit] I replaced the sensor.

 

A week or so later, the CEL comes back on, same trouble code. Same result from the FSM..

 

Any ideas?

 

 

I forgot to mention: 2001 forrester

If it continues to come back it probably needs to be replaced.

If ti says 02 sensor failure 99% of the time its right.

 

How many miles on the car

 

 

nipper

How many miles on the car

nipper

 

96K

 

I added a significant detail to the 1st post - I replaced the sensor. Then the CEL came back on today.

You should also check the connnection between the sensor and the ECU. If you replace the sensor, but there is no connection, you will still be having a problem. Your first post did not explain whether or not you had checked the wiring.

 

matt

[...]I replaced the sensor.

Did you use an OEM sensor for the replacement?

 

Had any other work been done on the engine immediately preceeding the P0133 code showing with the original sensor?

 

Do you have to add engine oil between changes, or is there even just a noticable drop on the dipstick? If so, how much?

 

Have you noticed any change in gas mileage or performance since the code appeared?

P0133 is slow response on a sensor. Some aftermarkets have given this code. I know I'll hear from a few, but for the O2 sensors, the Subaru ones do cost a little more, but work properly. Like a Subaru Head gasket vs felpro or others I have replaced.

[answering several question]

 

I didn't check the wiring - I figured that an open or short would have given me one of the other codes for those conditions.

 

I replaced the original with a Bosch from NAPA. It was around $80.00. It looks the same, but that doesn't mean much.

 

The engine has not been burning oil.

 

Not sure if I'm being paranoid, but maybe sometimes not as smooth as I remember. My wife drives the car 90% of the time, so I may have to "take it over" for a few days.

 

I reset the CEL the night I put up the original post, it isn't on yet today. At least 2 start / run /stop cycles.

My bad. I did not look up the code, to find out that it was O2 sensor slow response. The only other thing to do is check for exhaust leaks prior to the O2 sensor, which you would probably be hearing already!!!

 

I agree with the others. If it fails to clear up, try another O2 sensor. Maybe OEM if available. But I would try resetting the CEL once or twice more. Maybe the new sensor needs time to "break in..."

 

Matt

I'm not sure, but I think this model has two oxygen sensors, one upstream of the cat, and one downstream. If this is true, did you find & change the right sensor?

I'm not sure, but I think this model has two oxygen sensors, one upstream of the cat, and one downstream.

 

Yes, it has the before and after. I learned about that a while (year or 2) back, when the CEL came on with the code that says the cat isn't working good enough. I got the new cat at cost since the car was just out of warranty (used, not new).

 

I replaced the front sensor for this new trouble code, as the FSM states.

 

So far, the CEL is still off, at least another 2 cycles on the car.

 

I initially thought this OBDII stuff would be an improvemnet over the basic system in my loyales, but I am beginning to think that this is not so. I am going to keep my EA82's running as long as possible.

Yes, it has the before and after. I learned about that a while (year or 2) back, when the CEL came on with the code that says the cat isn't working good enough. I got the new cat at cost since the car was just out of warranty (used, not new).

 

I replaced the front sensor for this new trouble code, as the FSM states.

 

So far, the CEL is still off, at least another 2 cycles on the car.

 

I initially thought this OBDII stuff would be an improvemnet over the basic system in my loyales, but I am beginning to think that this is not so. I am going to keep my EA82's running as long as possible.

 

hate to tell you, but a failed cat code is 95% of the time a bad o2 sensor.

 

nipper

hate to tell you, but a failed cat code is 95% of the time a bad o2 sensor.

 

nipper

 

Just adding to make sure we are all on the same page:

 

The earlier bad cat code (I don't remeber the number any more) was like 2 years ago, and went away when I replaced the cat. The mechanic at the place I got the car did a bunch of checking and was in agreement to replace the cat.

 

I guess what you are saying, if you are referring to this earlier problem, is that the rear O2 sensor could be out of calibration, making the ECU think the cat was bad?

Just adding to make sure we are all on the same page:

 

The earlier bad cat code (I don't remeber the number any more) was like 2 years ago, and went away when I replaced the cat. The mechanic at the place I got the car did a bunch of checking and was in agreement to replace the cat.

 

I guess what you are saying, if you are referring to this earlier problem, is that the rear O2 sensor could be out of calibration, making the ECU think the cat was bad?

it can be either o2 sensor. The first o2 sensor runs the ecu, the 2nd checks the cat performance against the first. Since the first is in unprocessed exhaust it tends to ware out earlier and give false readings, hence giving a bad cat signal.

We/me/us recomend replacing the front o2 sensor and see if it goes away, since even if it is a bad cat, odds are its going to need a new o2 sensor anyway.

 

nipper