P0420 OBD II Code

jfreg · 04:28 PM

Check engine light in my '97 328i came on today. Code PO 420, "catalyst system below efficiency," came up on my tester. I've read that O2 sensor problems or leaks in the exhaust could cause that code to come up, even when catalytic converter is OK. Besides looking for leaks, and maybe inspecting the O2 sensors for major corrosion, what can be done to pinpoint the problem? The car has 102K miles, so I'd imagine the sensors are about due for replacement. Really hoping it's not the cat itself.

jfreg · 12-11-2007, 01:36 PM

Anyone?.....Anyone????

Jeron · Jeron's Garage

Theres a lot of good info on the web but it sounds like you've read some of it.

If it were me I'd:
1) clear the code and see if it comes back
2) probe the O2 two post cat sensors and see which one is reading low
3) clean the low O2 sensor
4) replace the low O2 sensor with a generic(cheaper) one
5) drive the car really hard to get the cats good and hot (this one wouldn't do any good for me because I do it all the time but maybe it could help you )
6) get an aftermarket cat

Jeron · Jeron's Garage

Oh and is P0420 not PO 420. I'm gonna fix your title. That may help your search for info too.

whosyadadie01 · 12-11-2007, 10:09 PM

Quote:

Originally Posted by Jeron

Theres a lot of good info on the web but it sounds like you've read some of it.

If it were me I'd:
1) clear the code and see if it comes back
2) probe the O2 two post cat sensors and see which one is reading low
3) clean the low O2 sensor
4) replace the low O2 sensor with a generic(cheaper) one
5) drive the car really hard to get the cats good and hot (this one wouldn't do any good for me because I do it all the time but maybe it could help you )
6) get an aftermarket cat

DO NOT use generic o2 sensors, use only origional sensors sold on this site or from a dealership... i did the whole cheap sesnsor thing and it caused so many problems i regret it. cause misfires on 3 cylendars and ****ed up my tranny

jfreg · 12-12-2007, 08:13 AM

Thanks for the advice. I'll let you know how it turns out. I've spent more time under this car since I got it last month than actually driving it.

whosyadadie01 · 12-12-2007, 09:02 AM

yea me to but it was more time trying to figure out what was wrong then actually driving

jfreg · 12-20-2007, 02:45 PM

Here's an update: It's been more than a week since I took step one of Jeron's advice, and cleared the trouble code on the OBD. The Check Engine light hasn't come back on, so I may be in the clear. The car is running well...knock on wood. Thanks all.

Jeron · Jeron's Garage

It'll probably show up when the weather changes, although I would think the cold would be the worst.

m3lar · m3lar's Garage

this just happened on my wife's 328i and I had two shops confirm it was the cat. One was a muffler shop that could read the codes and I wasn't convinced so I had a "tuning" BMW specialist shop read the code and they confirmed it for me. The Muffler shop was able to put in a universal cat and it cost $470 out the door. Sorry to hear about the problem and I hope this helps.

Larry

m3lar · m3lar's Garage

this just happened on my wife's 328i and I had two shops confirm it was the cat. One was a muffler shop that could read the codes and I wasn't convinced so I had a "tuning" BMW specialist shop read the code and they confirmed it for me. The Muffler shop was able to put in a universal cat and it cost $470 out the door. Sorry to hear about the problem and I hope this helps.

Larry