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2004 V70 AWD with P0420 code V70-XC70 2004

posted by Marlin Mangels on Fri Oct 9 04:25 CST 2020
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last visit: Tue Oct 21 15:41 CST 2014

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I ran this car for 2 years with a warped head that allowed some coolant into combustion chamber on #3 and slightly lower compression on #4. Head planed, new PCV system, new valves. Car runs great but throws a P0420 code every 400 miles or so. Mileage is good at 27 on the road. Total mileage on car 248K. Runs & idles great. I need help identifying if code is caused by cat or O2 sensor (or some other cause). Thanks for any help.
Marlin

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2004 V70 AWD with P0420 code V70-XC70 2004

posted by KlausC on Fri Oct 9 09:31 CST 2020
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last visit: Fri Oct 24 10:15 CST 2014

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It could be the front O2 sensor. It could be a leak in the exhaust before the cat. If the front O2 sensor is more than 100K miles old, replace it.

My 1995 850 throws a P0420 when I chug along in rush hour traffic at a steady 10mph or less. I have no idea why! Fortunately, I no longer have to drive to work.
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Keeping it running is better than buying new

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2004 V70 AWD with P0420 code V70-XC70 2004

posted by Marlin Mangels on Sat Oct 24 14:52 CST 2020
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last visit: Tue Oct 21 15:41 CST 2014

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How do I disconnect the O2 sensor from the electrical harness? I can see the connector from above, but it's hidden behind the bevel gear from below. Does it just pull apart or is there some sort of latch? The replacement has some sort of mounting bracket that has plastic press-in mounts. Thanks.
Marlin

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2004 V70 AWD with P0420 code V70-XC70 2004

posted by KlausC on Thu Oct 29 13:18 CST 2020
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https://www.youtube.com/watch?v=XPOG5Cs-u5w
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Keeping it running is better than buying new

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2004 V70 AWD with P0420 code V70-XC70 2004

posted by Marlin Mangels on Fri Oct 30 17:18 CST 2020
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last visit: Tue Oct 21 15:41 CST 2014

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Thanks for the video. The O2 sensor did not resolve the error code. Is the next step the catalytic converter?

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2004 V70 AWD with P0420 code V70-XC70 2004

posted by KlausC on Sat Oct 31 10:30 CST 2020
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last visit: Fri Oct 24 10:15 CST 2014

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It depends. If you live in a 'testing' state, you will have a problem. CA only allows OEM converters, quite expensive! Aftermarket cats are reasonably cheap, but only last for a few years. I would call junk yards for a used OEM version with 'low' mileage version.

In states with no inspections, you might want to install a rear O2 sensor extender. That takes the O2 sensor out of the exhaust stream so that the readings do not fluctuate.

It is quite possible that 'burning' antifreeze for 2 years clogged up the cat.
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Keeping it running is better than buying new

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2004 V70 AWD with P0420 code V70-XC70 2004

posted by will rehsper on Fri Oct 9 05:36 CST 2020
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last visit: Tue Jul 3 14:55 CST 2012

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Hiya Marlin, Nice to hear that you resolved your head gasket leak and the V70 is fully back in business!

Sounds like it could be that the cat is inefficient and doesn't want to chase mice anymore, but I wouldn't go replacing it just yet. If it only throws the code at that interval and with that fuel economy (which is excellent for an AWD BTW!), I might try and live with it.

Assess the condition of the O2 sensor(s). Are they original? Worth replacing the front one at least. Perhaps research what repeated washings with coolant will do to one... Then for good measure look things over for an air intake leak (if there is one, it'll be small).

-Will

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XC60 / Odyssey

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2004 V70 AWD with P0420 code V70-XC70 2004

posted by Marlin Mangels on Sat Oct 10 05:42 CST 2020
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last visit: Tue Oct 21 15:41 CST 2014

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Yes, it took me a while to decide to jump into the head rebuild. I was trying to decide if the sleeve was cracked or head gasket problem. Once the shop examined the head, the problem was obvious. Head planed, new valves, gaskets, entire PCV system. $1500 for everything. I didn't think that was bad.

I ordered the front Bosch O2 sensor.

Thanks.
Marlin

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