Code PO 420

buffmont · Post by **buffmont** » 28 Jan 2016, 14:25

Hello, I have a 99 V70 Non- Turbo, 119,600 miles. Runs very well. Last night the check engine light came on. No overheating rough running or starting or oil lights etc.

Took it to a mechanic he says the CODE is PO420, Cat not running efficiently.

Also said that that code is sometimes in error common on this model and the Cat is probaby allright, no smell or rough running or over heat.

Since new Cats are $1500 and the car is worth $2500 he said just ignore the light , it may go out, and since I dont have to go to emissions until Oct 2017, just live with it and make the decision then.

I saw something on an internet search about adding a spacer for the rear oxy sensor and ...pour lacquer thinner in the gas tank !!!!!!!

Any input will be appreciated , Thanks.

Post by **FLXC90** » 28 Jan 2016, 14:30

I would suggest checking your O2 sensors first. Use a scanner that tracks live data. Or just presume that at 100k plus, the rear sensor is dead.

Post by **rspi** » 28 Jan 2016, 14:37

My car had that code. It also had an aftermarket cat. Kept coming back until I replaced the cat.

Post by **E Showell** » 28 Jan 2016, 15:07

Car's not in Colorado, right? No cannabis smell from the CAT?

Post by **cvergi01** » 28 Jan 2016, 21:26

lol, I was wondering why my car was so sluggish!

Herb Goltz · Post by **Herb Goltz** » 29 Jan 2016, 08:02

P0420 can be a pain. The advice to check the sensor output is sound-- easy enough to do with an ELM327 code reader and the Torque app. Chances are your catalytic converter is toast-- you can use an infrared thermometer to check for temperature differences between the inlet and the outlet of the converter with the car at operating temperature. If the cat is good, you should see about 200 F difference, with the ouput being hotter than the input.

I would also have a look for any other OBD codes that might tell you what did the cat in.

I've had good luck with weld-in Magnaflow converters-- they run around $250 installed around here.

Post by **abscate** » 29 Jan 2016, 09:36

Clear it and see how long it takes to come back. If its more then 200 miles, you can probably get through inspection ok.

My P0455 comes every other 2000 miles .....so I just time my inspections or use my "up to 2 monitors not ready allowed' card here in the US of A.

Post by **cn90** » 29 Jan 2016, 09:45

"Cat" code is usually defective O2 sensor(s), simply b/c the cat itself has no sensor, it relies on upstream and downstream O2 sensor to monitor the cat's performance.

Herb Goltz · Post by **Herb Goltz** » 29 Jan 2016, 10:50

I would say that P0420 in isolation is more likely to be the cat than the sensors, which will throw their own codes (my 2000 V70 NA did). You can infer cat failure from a downstream sensor whose output mirrors the input sensor (both swinging sinusoidally-- the rear sensor shouldn't if the cat is doing its job).

buffmont · Post by **buffmont** » 31 Jan 2016, 10:07

Well , thanks for all the good advice from contributors regarding this post.

Ironically a blurb I saw on the internet while researching something called CATACLEAN, one of the reviewers suggested some full throttle drag race starts to redline to blow out the Cat.

So I did four starts flooring it till 75 and ,duh. The check engine light went out , so far.