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Discussion Starter · #1 ·
About two days ago my wife said the engine on our 2012 Wrangler Unlimited sounded louder than normal and the check engine light came on. We had the code read and found it's P0432 Bank 1. She drove it yesterday and for part of the day the check engine light was still on. She said yesterday the light went off but the engine or fan still sounds a bit louder than normal although she said she hasn't noticed any difference in performance the whole time. Today she said the engine still sounded loud and the light was still off, but she felt like the heater wasn't running consistently. Anyone have any ideas? If the check engine light went off I'm not sure that the catalytic converter is having any issues.
Thanks
 

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:welcome: to the Forum..:wavey:

Congrats on owning a Wrangler!

The P0432 code means that your catalytic converter for bank 2 of your engine is performing below what it should be. Generally, this is a sign that the converter has failed, but the problem may be related to an oxygen sensor
 

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About two days ago my wife said the engine on our 2012 Wrangler Unlimited sounded louder than normal and the check engine light came on. We had the code read and found it's P0432 Bank 1. She drove it yesterday and for part of the day the check engine light was still on. She said yesterday the light went off but the engine or fan still sounds a bit louder than normal although she said she hasn't noticed any difference in performance the whole time. Today she said the engine still sounded loud and the light was still off, but she felt like the heater wasn't running consistently. Anyone have any ideas? If the check engine light went off I'm not sure that the catalytic converter is having any issues.
Thanks
Hi LUNCHBOX111,
We're sorry to hear about your experience. Are you considering having your dealer take a closer look? If so, please keep us updated. If additional assistance is needed, feel free to send our team a private message.
Alex
JeepCares
 

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Discussion Starter · #4 ·
I apologize, the error code was a P0420. I’ve seen a whole lot of different posts about what could cause this code to trip and wanted to start with the cheapest thing to check first; especially with the holidays approaching anyone have any suggestions?
 

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PO420 is a failing Catalytic converter, but the interesting part is your heat.


If for any reason your temp sensor isn't sending a correct temp reading you could end up with a p0420 since the senors use coolant heat as a comparison.


Is your coolant low?


What do you mean "loud".... fan running on high all the time or loud exhaust system?
 

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If for any reason your temp sensor isn't sending a correct temp reading you could end up with a p0420 since the senors use coolant heat as a comparison.
I have never heard that. Looking at a factory service manual for the 3.6 and nothing about the temp sensor for a P0420.

The P0420 is usually always the catalytic converter. There is the corner case where there is an air leak in the exhaust tube or something wrong with the o2 sensor but it's one of the few codes that points to a specific part.

When checking these, you look at the o2 sensors and see if they report a lean condition when pulling a vacuum tube or a rich condition when doing a snap throttle. Then you look for to see if downstream mirrors the upstread sensors too closely. If all that checks out, it's time for new Cats.
 

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I have never heard that. Looking at a factory service manual for the 3.6 and nothing about the temp sensor for a P0420.

......
P0420 Catalyst System Efficiency Below Threshold (Bank 1)



A code P0420 may mean that one or more of the following has happened:

- Leaded fuel was used where unleaded was called for (unlikely)
- A damaged or failed oxygen / O2 sensor
- Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
- The engine coolant temperature sensor is not working properly
- Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe Failed or
underperforming catalytic converter (likely)
- Retarded spark timing The oxygen sensors in front and behind the converter are reporting
too similar of readings
- Leaking fuel injector or high fuel pressure Cylinder misfire Oil contamination
 

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Where did you pull that from? I have never heard that. This vehicle or others. From what I understand (so I am curious your source), is the PCM compares upstream and downstream o2s and looking for the downstream to oscillate less or not at all. That is why functioning o2 sensors are important. The only reason I can possibly think that engine temp is important is engines are more efficient (emissions wise) with a hotter temp. In a sense a hot engine is necessary to get a Cat hot, however, the PCM will see issues at both O2 sensors. The FSM I have says that the engine temp is necessary to monitor the CATs, otherwise it won't monitor for cat efficiency and it won't set the P0420. It will probably set a different code.


Here is from my 2014 Factory Service Manual that covers 3.6L.



Possible Causes

O2 SENSOR 1/1 RETURN CIRCUIT SHORTED TO GROUND
O2 SENSOR 1/2 RETURN CIRCUIT SHORTED TO GROUND
O2 SENSOR 1/1 RETURN CIRCUIT OPEN
O2 SENSOR 1/2 RETURN CIRCUIT OPEN
EXHAUST LEAK
ENGINE MECHANICAL CONDITION
AGING O2 SENSOR
CATALYTIC CONVERTER
 

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Where did you pull that from? I have never heard that. This vehicle or others. From what I understand (so I am curious your source), is the PCM compares upstream and downstream o2s and looking for the downstream to oscillate less or not at all. That is why functioning o2 sensors are important. The only reason I can possibly think that engine temp is important is engines are more efficient (emissions wise) with a hotter temp. In a sense a hot engine is necessary to get a Cat hot, however, the PCM will see issues at both O2 sensors. The FSM I have says that the engine temp is necessary to monitor the CATs, otherwise it won't monitor for cat efficiency and it won't set the P0420. It will probably set a different code.


Here is from my 2014 Factory Service Manual that covers 3.6L.



Possible Causes

O2 SENSOR 1/1 RETURN CIRCUIT SHORTED TO GROUND
O2 SENSOR 1/2 RETURN CIRCUIT SHORTED TO GROUND
O2 SENSOR 1/1 RETURN CIRCUIT OPEN
O2 SENSOR 1/2 RETURN CIRCUIT OPEN
EXHAUST LEAK
ENGINE MECHANICAL CONDITION
AGING O2 SENSOR
CATALYTIC CONVERTER

Google is your friend:


Causes & Symptoms

Aside from a bad catalytic converter, there are other causes of P0420. For instance, your vehicle may have exhaust pipe leaks, exhaust manifold leaks, engine misfiring, catalytic converter oil contamination, bad oxygen sensor, bad engine coolant temperature sensor, fuel injector leak, high fuel pressure, and bad oxygen sensor connectors. Sometimes even putting the wrong type of fuel in your gas tank can make trouble code P0420 occur.
https://cartreatments.com/p0420/


Less Common Causes


  • Retarded Spark Timing
  • Leaded Gasoline Used
  • Leaking Exhaust System
  • Malfunctioning CAT
  • Weak or Poor Spark
  • Coolant Temperature Sensor
Check Engine Code P0420 Explained - Causes and Fixes


Possible Causes


  • Leaded fuel used when unleaded is recommended
  • A broken or disconnected oxygen (o2) sensor
  • A broken or disconnected engine coolant temperature sensor
  • exhaust manifold leaks
  • Worn or damaged catalytic converter
  • exhaust piping leaks
  • Retarded/Improper spark timing
  • Leaking fuel injector
  • High fuel pressure
  • Cylinder misfire
  • Oil contamination
https://howtune.com/articles/182-diagnose-a-p0420-check-engine-code-on-a-odb2-car


https://www.obd-codes.com/p0420


What causes the P0420 code?


  • Damaged muffler or leaks in the muffler
  • Damaged exhaust manifold or leaks in the exhaust manifold
  • Damaged exhaust pipe or exhaust pipe leaks
  • A misfire in the engine
  • Oil contamination in catalytic converter
  • Faulty catalytic converter (most common)
  • Faulty engine coolant temperature sensor
  • Faulty front oxygen sensor
  • Faulty rear oxygen sensor
  • Damaged oxygen sensor wiring
  • Oxygen sensor wiring that is not properly connected
  • Damaged oxygen sensor connectors
  • A fuel injector that is leaking
  • Fuel pressure that is high
  • Use of the wrong kind of fuel (using leaded fuel instead of unleaded fuel)
https://www.autoblog.com/2016/04/06/p0420-obd-ii-trouble-code-catalyst-system-efficiency-below-thre/


Q: My car shows a P0420 code and the engine coolant temperature reading (via torque pro app and elm327 Bluetooth reader) stayed at 84.2 degrees




A: Hi there - "boundary measured engine temperature," or the lowest temp reading a sensor can transmit, can be different based on each temperature sensor. The issue here is what is the true engine temperature? Is the thermostat getting the engine up to its design temperature (something near 205 degrees Fahrenheit/100 Centigrade). Can you cross-check the engine temperature with a laser thermometer, cockpit temperature gauge (middle of the gauge usually), or other measuring device? If the engine is truly coming up to 200 degrees (F) or so, then yes, the ECT can read "low" to the computer, causing rich mixture running. This could cause a low catalytic converter efficiency problem if the engine has run rich for a while.
https://www.yourmechanic.com/questi...th-reader-stayed-at-84-2-degrees-by-timothy-s


How To Correct P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Here are some ways with the help of which you will be able to correct the OBD Code P0420:


  • Replacing the damaged muffler or repairing the leaks in the muffler
  • Repairing the leaks or damages in the exhaust manifold
  • Rectifying the leaks or repairing the damages in the exhaust pipe
  • A most common reason – replacing the damaged catalytic converter
  • Changing the damaged engine coolant temperature sensor
  • Substituting with a good front and rear oxygen sensor connectors
  • Replacing or repairing the leaky fuel injectors
  • Diagnosing the damaged parts and problems due to misfire
  • Checking and rectifying the other trouble codes which are stored by the Powertrain Control Module (PCM)
https://partsavatar.ca/p0420-obd-ii...below-threshold-bank-1-solution-oxygen-sensor
 

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Google is your friend:
I can google, but I always take those type of sites with a grain of salt. Many times I look at them the description isn't close to what is in the factory service manual. Not sure where they get their info.

In this case, I will stick with the FSM.

I will click some of your links cause I am curious when someone says check an ECT, I'd like to know what they are thinking. In the case of 3.6L JK, the FSM clearly shows that the monitor won't run if it's below 158.
 

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I can google, but I always take those type of sites with a grain of salt. Many times I look at them the description isn't close to what is in the factory service manual. Not sure where they get their info.

In this case, I will stick with the FSM.

I will click some of your links cause I am curious when someone says check an ECT, I'd like to know what they are thinking. In the case of 3.6L JK, the FSM clearly shows that the monitor won't run if it's below 158.

It's not just jk. It's all of them. Of course the minimum temps differ a little fromm vehicle to vehicle but it's all the same. All vehicles run open loop till a particular temp is hit. Nothing new or different with jk


BTW... what "FSM" are you speaking of? That service manual on disc? If that's the one you're talking about.... I have it (for a 2017) and it sucks. I can't remember what I paid for it, but I sure do remember feeling utterly disappointed and ripped off when it came and I had a look at it.
 

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It's not just jk. It's all of them. Of course the minimum temps differ a little fromm vehicle to vehicle but it's all the same. All vehicles run open loop till a particular temp is hit. Nothing new or different with jk
Understand but this is kind of my point with the ECT affecting a P0420. It won't even monitor it as an issue unless the engine was at temp. If the ECT is not sending a signal, it will flag a code for that. If the temp takes too long to get hot, the PCM will flag a thermostat rationality code. The computers have a good amount of certainty that the cats are bad before the code gets set in my opinion.


BTW... what "FSM" are you speaking of? That service manual on disc? If that's the one you're talking about.... I have it (for a 2017) and it sucks. I can't remember what I paid for it, but I sure do remember feeling utterly disappointed and ripped off when it came and I had a look at it.
I ordered the official FSM off techauthority. I really like it. Curious what you don't like about it. Are you looking in the right spots for info? The reason I ask is I have noticed the good nuggets of info are sometimes in random places. Sometimes it's in description/operation, while other times it's in the diagnosis section, or in wiring diagrams.

My only complaint other than cost is that some of their diagrams aren't the best when looking to find how something is installed. The OEMs are getting better cause at least now their graphics have different colors or shades for different parts. When it was just black and white 10 years ago, that made it tough to understand what I was looking at.

I do like the wiring diagrams, many of their descriptions on how systems work is good. For example the evap system has pretty good detail. It's strange that it's in the diag section next to the p04xx codes. Also like the fact that it doesn't have some of the misleading info that I find in forums or OBD type websites. The wiring connector info is impressive along with the routing of harness and location of connectors.
 

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Understand but this is kind of my point with the ECT affecting a P0420. It won't even monitor it as an issue unless the engine was at temp. If the ECT is not sending a signal, it will flag a code for that. If the temp takes too long to get hot, the PCM will flag a thermostat rationality code. The computers have a good amount of certainty that the cats are bad before the code gets set in my opinion.
If the system is jumping back and forth between open loop and closed because of a faulty temp sensor.......





I ordered the official FSM off techauthority. I really like it. Curious what you don't like about it. Are you looking in the right spots for info? The reason I ask is I have noticed the good nuggets of info are sometimes in random places. Sometimes it's in description/operation, while other times it's in the diagnosis section, or in wiring diagrams.

My only complaint other than cost is that some of their diagrams aren't the best when looking to find how something is installed. The OEMs are getting better cause at least now their graphics have different colors or shades for different parts. When it was just black and white 10 years ago, that made it tough to understand what I was looking at.

I do like the wiring diagrams, many of their descriptions on how systems work is good. For example the evap system has pretty good detail. It's strange that it's in the diag section next to the p04xx codes. Also like the fact that it doesn't have some of the misleading info that I find in forums or OBD type websites. The wiring connector info is impressive along with the routing of harness and location of connectors.

I find it EXTREMELY lacking in any kind of detail all over the place.


Here's my factory manual from my previous vehicle... 2 volumes... over 7000 pages. That tech authority disc is an embarrassment by comparison.
You wanna know how to do gears or similar... youtube is a better bet than that disc!
20170923-120131.jpg






I think BBB industries has changed slightly now but up until about 8 months ago you could get more complete wiring diagrams through them... free of charge , no less.
 

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If the system is jumping back and forth between open loop and closed because of a faulty temp sensor.......








I find it EXTREMELY lacking in any kind of detail all over the place.


Here's my factory manual from my previous vehicle... 2 volumes... over 7000 pages. That tech authority disc is an embarrassment by comparison.
You wanna know how to do gears or similar... youtube is a better bet than that disc!
View attachment 4185477






I think BBB industries has changed slightly now but up until about 8 months ago you could get more complete wiring diagrams through them... free of charge , no less.

I think we have had this argument before...
 

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I think we have had this argument before...

Could be.
It's not the first time I have expressed utter disappointment in that disc. If its price tag was more along the lines of a haynes paper back service manual then I would expect the crappy hand drawn imagery and lack of detail. But for a "professional" service manual with a professional price tag, there is no excuse.
 

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I agree that P0420 mainly means that the catalytic converter or several parts of it stopped working the way they should. also this can happen due to a lot of reasons.
The oxygen sensor or both of them have failed or have been damaged.
One of the sensors isn’t connected properly so there’s a problem with the wiring.
The temperature sensor on the engine isn’t working properly.
 

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Welcome to the Forum!
 
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