I like that story. Has come up in just about every war. At least since the Korean war anyway.

 

Check engine light went on the other day so I went and got the code read. P0420. I did some reading and also talked to Justin (Dukie) and it looks like it's either going to be the catalytic converter or the downstream O2 sensor. How do I figure out which one it is?

Jeep just turned 101,000 miles. Original exhaust and O2 sensors.

 

 

The PCM compares switch rates between the front O2 sensors and the downstream catalyst monitors. The catalyst monitors are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exhaust, and how much it is affecting the exhaust. If it sees little or no effect on the exhaust gases that have passed through the cat, then it decides that the cat is not working anymore, and sets a P0420, or a P0430, depending on which bank it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you probably need a catalytic converter.

 

Upgrade exhaust, and change O2 sensors and be done.

 

http://www.urdusa.com/Electronics-Re...170/index.html

 

It's money I didn't want to spend right now to be honest. I was hoping to be able to test it so I could buy just the failing part...the downstream sensor or the cat.

 

If you look at the maintenance list, O2 sensors are a 60k mile replacement part. $60ea

 

Told you how....

 

Brian, lemme know if its the cats (its one piece) i gots a hook-up--


opps, mebbe its not,mine was though, regardless, i gots a hook-up

 

I don't have a scanner with a data stream to test it. Is it possible to test it with a multimeter?

 

I know Autozone rents out other tools, not sure about a scanner. Worth checking out tho

 

You could....you would see the front switching....the the rear staying mostly at -.05v. If you get nothing out of the rear, it is bad...if you get it switching, cat is bad....

Can you go to Advance and borrow one?

 

I know Advance does....they ask to hold your License while you have it.

 

Just did the plugs in new xj,PO had them gapped a .70 is there any reason they were twice what they should've been?