Engine Code P0432

[Nick B]

For the past few months I have had check engine code P0432 on a 2000 TJ 4L and haven't done anything about it until recently. On the OBDII scanner it says "Main Catalyst Efficiency Below Threshold Bank 2"

The previous owner installed new cats and y pipe about 2 years ago and they only have about 5k miles on them. They also replaced all O2 sensors but not with the correct NTK ones. I replaced the downstream one in bank 2 with a NTK one hoping that would fix the issue. The old one was damaged so I figured this was the problem but about 50 miles later the light came back.

I plan to replace the upstream one also but don't want to keep buying parts if they don't need to be changed out. If anyone else has had this issue and fixed it please chime in. I know that it's not super important to fix but I would just like to turn that yellow glow off the dash.

 

[RubiconSpyder]

For the past few months I have had check engine code P0432 on a 2000 TJ 4L and haven't done anything about it until recently. On the OBDII scanner it says "Main Catalyst Efficiency Below Threshold Bank 2"

The previous owner installed new cats and y pipe about 2 years ago and they only have about 5k miles on them. They also replaced all O2 sensors but not with the correct NTK ones. I replaced the downstream one in bank 2 with a NTK one hoping that would fix the issue. The old one was damaged so I figured this was the problem but about 50 miles later the light came back.

I plan to replace the upstream one also but don't want to keep buying parts if they don't need to be changed out. If anyone else has had this issue and fixed it please chime in. I know that it's not super important to fix but I would just like to turn that yellow glow off the dash.

View attachment 134831

Did you ever get a fix? I’m starting down the rabbit hole with a P0432 code..

 

[sawmillman]

You probably already know this, it's telling you the cat on the back 3 cylinders is not burning the exhaust enough to clean it to standards. Here's what got rid of mine. Go to the Help aisle at Advance auto parts. Get a pack of non-foulers comes in a 2 pack, Dorman 42009. Drill out the center with a .500 bit. Screw it in the sensor bung (the one after the cat) and then screw in the sensor. Some people have had to stack both the non-foulers but using the one worked on mine.

 

[RubiconSpyder]

Did not know that fix...was going to invest in 02 sensors and CAT's...

 

[sawmillman]

It backs the sensor out of the direct exhaust stream. Can't guarantee it will always work but it's only like a $4 investment.

 

[RubiconSpyder]

I see, so root cause is not the cats or the sensor, just position?

 

[sawmillman]

No the root cause is prob the cat. The pre and post sensors compare notes on the exhaust going into and out of the cat. When you move the sensor back it can fool it.

 

[RubiconSpyder]

No the root cause is prob the cat. The pre and post sensors compare notes on the exhaust going into and out of the cat. When you move the sensor back it can fool it.

Gotcha...I appreciate the tip...thanks!

 

[fizzlebottom]

You only replaced 1 of the 4 O2 sensors with the correct one. I really would replace the upstream bank 2 sensor with the correct one and then report back. They act as a "before" and "after" set and report the difference to see if the catalytic converter is doing its job properly. With the wrong O2 sensors, the "before" reading may be completely off. You should make sure all sensors are working properly before trying to trick your computer with non-foulers.

 

[RubiconSpyder]

The fouler is a good workaround, It can get you out of a bind...time to take a deep dive into analyzing the problem..im going to start by testing each sensor ( continuity and OHM's)...if no bad sensors are found, its either a PCM or bad precats...

 

[fizzlebottom]

The fouler is a good workaround, It can get you out of a bind...time to take a deep dive into analyzing the problem..im going to start by testing each sensor ( continuity and OHM's)...if no bad sensors are found, its either a PCM or bad precats...

It has been documented pretty hard on this forum that if you use non-NTK/NGK O2 sensors, you're gonna have a bad time. So even if the incorrect sensors alone seem ok, they're not gonna give the PCM what it is looking for.

 

[RubiconSpyder]

It has been documented pretty hard on this forum that if you use non-NTK/NGK O2 sensors, you're gonna have a bad time. So even if the incorrect sensors alone seem ok, they're not gonna give the PCM what it is looking for.

I’m all over the NTK/NGK sensors...I have no service records on the sensors that are in there now...BTW helped a buddy and a few on the forum with other sensors problems..I either go OEM or better, never low grade..

 

[fizzlebottom]

I’m all over the NTK/NGK sensors...I have no service records on the sensors that are in there now...BTW helped a buddy and a few on the forum with other sensors problems..I either go OEM or better, never low grade..

I only mentioned that because it sounded like you jumped to bad PCM or precats without suggesting making sure all sensors are actually the correct ones needed.

And yeah, if new NTK/NGK sensors aren't solving the problem then it is likely a bad precat. I just went through that myself. Had a low efficiency code. Replaced all cats and all O2 sensors. No more codes, and it runs noticeably smoother.

 

[RubiconSpyder]

It did sound that way...testing the sensors was an intermediate step, I want to document the process for future TJ owners..replacement with NTK/NGK would come next...precuts and finally PCM of all else fails...I appreciate the feedback..

 

[RubiconSpyder]

Fizzle.. what cats did you go with. Eastern, magnaflow or flowmaster?

 

[fizzlebottom]

Fizzle.. what cats did you go with. Eastern, magnaflow or flowmaster?

I went with the Flowmasters. I have a 2005, and I learned that the later model TJs have their precats a few inches closer to the manifold. This, paired with the really big heat shields on the Flowmasters, made getting a few of the bolts in very tricky and uncomfortable. From pics I've seen, the <2004 precats are further down, providing a lot more room to get universal swivel joints in there. The Magnaflow units also look a hell of a lot nicer, but for the price I can't complain.