Replaced 02 Sensor, but ...

iceb52! · Post by **iceb52!** » 24 May 2005, 21:35

2000 V70 GLT, 128,000 miles. I have had a check engine light going off and on for over a year now. Some occasional surging in the engine. Auto ZOne read the code and it indicated a bad 02 sensor before the catalytic converter. I replaced the sensor last weekend. The check engine light is on again and this time it is code P0422 (or maybe P4022). Anyway, autozone said the code meant a bad catalyiic converter. Their book said it could be related to a "major vacuum leak, engine misfireing, or oil leaking past an exhaust valve??"

It doesn't seem like a coincidence that I replaced an 02 sensor before the catalytic converter and now I have a code indicating a bad catalyitc converter. Can anyone shed some light on my problem (s). Could there be a problem with the 02 sensor "after" the converter? My state does not have an emissions test.

Any info would be appreciated.

Post by **dosbricks** » 25 May 2005, 19:57

O2 sensors are in the hot exhaust stream so they age. The front and rear are comparing readings to make sure the cat is doing it's job. Sometimes a new front will be "out of range" with the old rear and require replacing the rear also. That said, the code should be "rear O2 sensor slow response" or something like that.

Nevertheless, the cat is so expensive, if it were me I would put in a new rear sensor (which if not needed now, soon will be) and see if that takes care of it. If that doesn't work you may be shopping for a good used cat.

PO422 is "main cat effiency". Running with a code caused by a vacuum leak (the most likely scenario on a car as new as yours) can cause the ECM to compensate with a mixture that is too rich. Over a long time that can cause damage to the cat.

Jot · Post by **Jot** » 25 May 2005, 20:16

PO422 "Main Catalyst Efficiency Below Threshold" .I just got the same code on a '00 GLT SE but if it was running rich wouldn't the fuel economy suffer? I have been getting 31 highway 28+ around town

Post by **dosbricks** » 25 May 2005, 20:33

Jot wrote:PO422 "Main Catalyst Efficiency Below Threshold" .I just got the same code on a '00 GLT SE but if it was running rich wouldn't the fuel economy suffer? I have been getting 31 highway 28+ around town

That's real good mileage. Running rich is only one ("most likely") possible cause. You guys have ETM on those `00's. Could that be connected since it has a history of problems?

White850Turbo · Post by **White850Turbo** » 26 May 2005, 06:51

I just realized what the problem is. I am pretty sure you have the Denso engine management system. I remember speaking with my indy a while back and he noted that cars using that EMS must have both o2 sensors replaced at the same time, otherwise the CEL will come on about a week later indicating rear o2 sensor failure or cat converter efficiency code.

gold850 · Post by **gold850** » 27 May 2005, 17:28

I had this problem but i got it fixed. I recieved a recall and took it in and they replaced it and fixed it right up. So you might want to check and see if youve had all the recalls done. I have a 96 850.

guest · Post by **guest** » 06 Jun 2005, 10:02

Driving a 2000 V70 XC Wagon. Got "Check Engine" and replaced BOTH O2 sensors. After two days, check engine comes on again and mechanic says "Cat" below minimum.
Can any one tell me what options I've got??
Thanks,

Post by **dosbricks** » 06 Jun 2005, 15:45

guest wrote:Driving a 2000 V70 XC Wagon. Got "Check Engine" and replaced BOTH O2 sensors. After two days, check engine comes on again and mechanic says "Cat" below minimum.
Can any one tell me what options I've got??
Thanks,

Try going back to have the code(s) read and post the numbers here. Get them cleared and then drive it and see if maybe they stay clear this time before investing in a catalytic converter.

martylandman · Post by **martylandman** » 13 Mar 2007, 16:31

gold850 wrote:I had this problem but i got it fixed. I recieved a recall and took it in and they replaced it and fixed it right up. So you might want to check and see if youve had all the recalls done. I have a 96 850.

I've got a '96 850 GLT and the only recalls I remember are one for the driver's seat warmer which I brought in, they fixed, and it promptly broke again; and one for the gas tank which I've not gone in for. Any others I should be aware of?

Also, on a related note to this main topic, my '96 850 was throwing a P0410. I looked at the SAS valve (couldn't see or hear anything looking at or shaking it) and put it back on w/o a replacement gasket. The old gasket was in pretty good, not perfect shape. Then I drilled two holes as recommended in the bottom of the air pump. I can, and could hear the air pump working, whining a little when the car's cold. No water came out after drilling those 1/8" holes. Not a drop.

After two resets the P0410 code went away. Now I am getting a P0422.

Even after resetting.. just a couple days later. I wonder if there may be a mild vacuum leak from not replacing the SAS valve gasket and if I could make do with a little blue gasket sealent to see if that fixes it?

Marty

Pegs850 · Post by **Pegs850** » 15 Mar 2007, 18:02

The P0422 TC is for a "three way catalytic convertor efficency" code as the earlier replys stated. I don't think it has anything to do with your airpump because the air pump's purpose it to pump air when the engine is just started and rather cold. It runs occasionally even when warm to check that it is operating OK. It should make the cat work better rather than worse even if it never shut off.

As for the vaccuum leak, the exhaust should actually be a slight positive pressure and not a vaccuum. At worst, you might be getting some exhaust coming out around the SAS valve if it had a poor seal. If so, it seems like you should be able so see some evidence of it (carbon build up). The air pump has no connection with the intake side other than to pull air from just after the air filter. I suppose exhaust could be blowing by the SAS, through your air pump and then ingesting it through the intake. While enough of it would definitly make the engine sick and likely upset the cat, it dosen't seem likely.

What say the forum gurus?