S70 Catalytic converter or O2 sensor

boynamedsue · Post by **boynamedsue** » 03 Feb 2010, 05:07

Had the CL light come on recently, and went to a chain auto parts store where they said it was a bad O2 sensor. I then went to a mechanic who yesterday said it was a bad cat and quoted me a $750 price tag. Is anyone familiar enough with codes to know what I should do? I will get the code today and post it. Sorry if there is already a thread out there about this, I didnt have time to search...
Thanks for any help though
1998 S70

Post by **jblackburn** » 03 Feb 2010, 07:20

Very rarely do converters actually go bad, unless they're flooded with water or your car has been running rich for a long time.

Smack the converter with your hand a couple times. If it sounds like loose pebbles or something in there, then it probably does actually need to be replaced.

I'm thinking you're getting a code for 'reduced cat efficiency' or something of that sort, but definitely post the code when you get it. The problem is probably actually just an old O2 sensor.

boynamedsue · Post by **boynamedsue** » 03 Feb 2010, 07:40

The code is P0422

Post by **boosted5cyl** » 03 Feb 2010, 08:03

Code: Select all

P0422 - Main catalyst efficiency below threshold (bank 1)

Could be cat, could be O2. Good news is that the code itself shouldn't affect peformance or economy. If the cats are clogged however that will noticably hurt economy and peformance. Cats can go bad before they break down or clog up. You could choose to ignore the code, however if further codes come up you will not be aware if them.

You never mentioned if your motor is a turbo or not....

From http://www.volvo-forums.com/t19926-p042 ... -light.htm

fromleftfield wrote:I have been chasing a P0422 on my 2000 XC70 (140K miles) for a few months.

I may have finally resolved it in the past week.

It was an obtuse, but inexpensive problem to fix.

My approach was to eliminate all the places where un-metered air could get into the intake manifold.... clean and clamp the vacuum hoses; etc.

After checking and rechecking everything, and making some significant improvements in the performance and economy along the way, I still got an occasional P0422 under specific driving conditions.

One more check last week and I discovered that one of the two plastic clips on the intake air temperature sensor was broken off.

I bought a new one from volvo for about $20. It took 2 minutes to replace.

With only one plastic clip, the sensor will work fine at highway speed and a good vacuum in the intake. At suburban driving, the seal is not so good, and a positive pressure in the intake (like when you let you foot off the gas), might even push the sensor partially out.

IMHO, the only way that sensor got broken was when it was in the dealer for service. From the looks of the break, it has been broken for a while.

I think that this solution to P0422 would more likely apply to turbo vehicles, as the non-turbo's would not have the positive pressure in the intake.

Good luck !

boynamedsue · Post by **boynamedsue** » 03 Feb 2010, 08:28

It's a non turbo with 295,000 miles
thanks for the info so far

Post by **boosted5cyl** » 03 Feb 2010, 09:01

boynamedsue wrote:It's a non turbo with 295,000 miles
thanks for the info so far

With 295K id be inclined to lean towards a cat replacement, or removal depending on your state

. You could start with the O2 I guess but 300K is a good run for a cat.

Post by **SilverS70** » 03 Feb 2010, 10:13

at 295k I'd guess it was the cat too. But check for exhaust leaks first because cats are expensive. Let us know how you resolve it.

boynamedsue · Post by **boynamedsue** » 03 Feb 2010, 11:28

after looking on different parts sites, there is a big fluctuation in the prices for cat converters. Anyone know the difference between the $175 and the ones over $600. They both say new, granted some are generic brands. Are there some to stay away from?

Post by **Pauloil** » 03 Feb 2010, 11:47

how is the car's performance? like boosted said "If the cats are clogged however that will noticably hurt economy and peformance"

it is poss to check cat. by removing O2 and checking the back pressure, most likely at a dealership

Your car has a lot of miles and you did not say it was not running well.
driving a car often and getting it hot is good for it and the cat.

larryh · Post by **larryh** » 03 Feb 2010, 19:30

on a car with that many miles. i'd go for a used cat from eirie vovo. they're guaranteed for life , and they're original equipment, which will be better than a brand new generic cat..