Jeep liberty O2 sensor help

[mike diesel]

My wife has a 2003 jeep liberty. It is the late 2003 model so it has the 42RLE trans.

Issue I am having is that it is throwing a p0420 code "Catalyst efficiency below threshold bank 1". This has California emissions so it has a cat in each down pipe with an O2 sensor before and after each cat.

Borrowed a scanner from a buddy to monitor O2 sensor operation. 3 of the sensors are reading like this. Switching back and forth between lean and rich, from what I can gather, this is their proper operation.



Sensor 2/2 (post cat bank 2) is reading this...



But the p0420 is corresponding to bank 1. So my question is, is this sensor reading properly? Or is it supposed to read like sensor 1/2 (post cat bank 1), or is sensor 1/2 supposed to read like 2/2 and that's why it is throwing the code?

I am stumped with this. Registration is due last month lol.

 

[mike diesel]

Ok, think I figured it out. Proper operation of the post cat sensor should be a nice flat line like I'm seeing on 2/2. Sensor 1/2 is reading just like the pre cat sensor indictating the cat on driver side is shot and not doing its job.

 

[clrussell]

Ok, think I figured it out. Proper operation of the post cat sensor should be a nice flat line like I'm seeing on 2/2. Sensor 1/2 is reading just like the pre cat sensor indictating the cat on driver side is shot and not doing its job.

Exactly


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[mike diesel]

Driver side cat is all jacked. Lucky me.

 

[Chevy1925]

glad we could help out Mike :rofl:

 

[mike diesel]

 

[THEFERMANATOR]

Theres a cheap fix for this, or you can do the right fix. The cheap fix is to go down and get a pack of spark plug anti-foulers. Drill one out to accept the O2 sensor, then screw that one into the un modified one, and put the minto the O2 bung and screw the O2 into them. This will slow down the O2 reading and stop it from coding. The correct fix is to replace the cat.

 

[Rancelot211]

Did this to an Audi I flipped worked like a charm^ sometimes you need to use two to space it out more

 

[onebaddmaxxx]

Theres a cheap fix for this, or you can do the right fix. The cheap fix is to go down and get a pack of spark plug anti-foulers. Drill one out to accept the O2 sensor, then screw that one into the un modified one, and put the minto the O2 bung and screw the O2 into them. This will slow down the O2 reading and stop it from coding. The correct fix is to replace the cat.

I could see this being an option if the o2 sensor was bad, but if the converter is bad your better off fixing it correct.

Mike you could swap the post o2 sensors and see if the issue stays on the same bank, or follows. If it follows, o2 sensor. If it stays, then converter.

Pre cat will me all over the place, post cat should always be fairly smooth.

 

[bfmine]

Same thing happened to my 03 wrangler. One of the pre cats decintegrated. They wanted like 900$ for that section of exhaust with the 2 cats in it. So I took a holesaw to the bung after the bad cat. Cut it out. Then cut out a hole next to the good cats 02 sensor (after cat) and welded the bung there. So now the side that decintegrated doesn't have an 02 sensor after the cat. And the cat that is still good has 2 o2 sensors behind it.

 

[mike diesel]

I did the correct fix. I replaced the cat. It was trashed. It looked like someone had poured white cement in it. I have no idea how the engine could even push exhaust through it.

The O2 sensor is reading perfect now. Luckily the cat is v-banded in, fairly easy to remove. The cat monitoring system readied itself after a 10 minute drive. Unlike before, it would never ready, then throw the light.

 

[mike diesel]

Sensors 1/2 and 2/2 are both nice flat lines now.

 

[THEFERMANATOR]

I could see this being an option if the o2 sensor was bad, but if the converter is bad your better off fixing it correct.

Mike you could swap the post o2 sensors and see if the issue stays on the same bank, or follows. If it follows, o2 sensor. If it stays, then converter.

Pre cat will me all over the place, post cat should always be fairly smooth.

It won't work with a bad O2 sensor. A bad O2 is a bad O2, nothing you can do except repalce it. Yes you're better off fixxing it, but all you have to do to stop the efficiency code is t oslow the movement of the downstream O2 sensor. The anti-foulers do just this. It's an old trick used so you can rmeove your cat without doing anything to the tuning for the downstream O2 sensors.

 

[THEFERMANATOR]

I did the correct fix. I replaced the cat. It was trashed. It looked like someone had poured white cement in it. I have no idea how the engine could even push exhaust through it.

The O2 sensor is reading perfect now. Luckily the cat is v-banded in, fairly easy to remove. The cat monitoring system readied itself after a 10 minute drive. Unlike before, it would never ready, then throw the light.

The BIG question is WHY did the cat do that? If you don't find the cause, then you're just goign to be doing it again later on. And most cat con warranties won't cover damage like this as it is an induced failure not caused by the cat converter.