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Discussion Starter #1
So I am having trouble with my car, a dodge charger rt v8 5.7 police package. The car gives me a code, P0420. Which is bank 1 catalytic converter not working right. I changed the catalytic converter and O2 sensor downstream (O2 sensor #2 bank 1). That took care of the code. So I thought. Recently the code came on again. Same one, P0420.
So I used a Bluetooth scanner and monitored the O2 sensors for both banks, 1 and 2. And again O2 sensor #2 bank 1 was jumping all over. So I was thinking that it has to be something else, like a vacuum leak somewhere in the exhaust pipe or a gasket. It could not be the catalytic converter that i changed a few months ago. So I took it to a mechanic shop today to get a profesional diagnosis. And at the end of the day they told me it's the catalytic converter, but the one in the other side (passenger side ) that i need to change. I asked them if they checked them both. They said they did some tests on them and the passenger side one didn't very good. Then I asked them, which side is bank 1 and which side is bank 2? They said bank 1 is the driver's side and bank 2 is the passenger's side. So if the code is for bank 1 why they are saying is the catalytic converter from bank 2. I asked if bank 2 would give me a different code or both use the same code. They said each bank has its own code. It doesn't make sense to me. They want to change the catalytic converter from bank 2 and the code is for bank 1 (the one that i changed before) changing that part will be like $600 they said. But if I change it and that wasn't the problem, I might just waste the money on it. Am I right? Bank 1 is the driver's side and bank 2 is the passenger's side. The engine is a hemi v8 5.7
So who's wrong? Me or the mechanics? Why they want to change a part that doesn't match with the code that I have? I asked them if the visually inspected the catalytic converters to see inside... they said they didn't. When I changed the catalytic converter from the driver's side I looked inside of it and it was all pieces. So I know for sure that was the right one to change. But now that is giving me the same code (p0420) and they want to change the passenger's side catalytic converter it doesn't make sense to me. Who's right? Me or the mechanics? The o2 sensor reading looks good for bank 2 and does not look good for bank 1. The code is for bank 1 and they want to change bank 2 catalytic converter. Any ideas of what is going on?
 

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Bank-1 is the driver side and Bank-2 is the passenger side for the 5.7L Hemi V8. Bank-1 is the exhaust bank with the number one cylinder and Bank-2 is exhaust bank with the number two cylinder. The 5.7L Hemi cylinders are numbered from front to rear; 1, 3, 5, 7 on the left bank (driver) and 2, 4, 6, 8 on the right bank (passenger).
P0420 is a code for Catalyst 1/1 Efficiency (driver side). As catalyst efficiency deteriorates, the switch rate of the downstream O2 sensor approaches that of the upstream O2 sensor. P0420 gets logged when the switch ratio between the two O2 sensors reaches a predetermined value.
Since you're logging live data on the O2 sensor PIDs you are able to see the values of the sensors. Are you able to see the upstream and downstream sensors or just Bank-1/Bank-2? You replaced the Cat and rear (downstream) sensor but a new rear O2 Sensor along with an aging front O2 Sensor may cause P0420 to get logged. An exhaust leak can also cause P0420 to get logged.
I would focus on Bank-1 (driver side). Check for exhaust leaks and if the front (upstream) O2 sensor is the original ... I would replace it. What O2 sensor brand are you using? Some aftermarket brands don't work as well as the Mopar OEM sensors.
You said "recently the code came on again". How much time has gone by since you replaced the Cat and O2 sensor?
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Discussion Starter #3
Bank-1 is the driver side and Bank-2 is the passenger side for the 5.7L Hemi V8. Bank-1 is the exhaust bank with the number one cylinder and Bank-2 is exhaust bank with the number two cylinder. The 5.7L Hemi cylinders are numbered from front to rear; 1, 3, 5, 7 on the left bank (driver) and 2, 4, 6, 8 on the right bank (passenger).
P0420 is a code for Catalyst 1/1 Efficiency (driver side). As catalyst efficiency deteriorates, the switch rate of the downstream O2 sensor approaches that of the upstream O2 sensor. P0420 gets logged when the switch ratio between the two O2 sensors reaches a predetermined value.
Since you're logging live data on the O2 sensor PIDs you are able to see the values of the sensors. Are you able to see the upstream and downstream sensors or just Bank-1/Bank-2? You replaced the Cat and rear (downstream) sensor but a new rear O2 Sensor along with an aging front O2 Sensor may cause P0420 to get logged. An exhaust leak can also cause P0420 to get logged.
I would focus on Bank-1 (driver side). Check for exhaust leaks and if the front (upstream) O2 sensor is the original ... I would replace it. What O2 sensor brand are you using? Some aftermarket brands don't work as well as the Mopar OEM sensors.
You said "recently the code came on again". How much time has gone by since you replaced the Cat and O2 sensor?
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It came like after 5 or 6 months that I changed those parts. I didn't changed the upstream sensor. I just did the catalytic converter and downstream sensor. I used one thai got from O'Reillys ... my question is that the code is for the driver's side, which is bank1 but the mechanics said that side it is working fine. The passenger's side isn't working right, which is bank2. And they want to change that catalytic converter. But the passenger's side isn't giving me any code. So why they want to change that if I don't have any code for it? And why they say that bank1 is fine if I have a code for it (p0420)
I think they didn't look for any vacuum leaks.
 

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Check for exhaust leaks between the engine and the O2 Sensors. Which brand Cat did you install? Local exhaust shop told me that some of the inexpensive high-flow Cats only last about six months before they start failing and causing codes to get logged.
I can't explain the discrepancy between the P0420 (Bank-1) and the mechanic's diagnosis of the problem being Bank-2. The mechanic has the advantage of being hands-on the vehicle and I can only go by the code that is logged by the car's onboard diagnostics.
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Discussion Starter #5
I think I'm going to take it to another mechanic shop for a 2nd diagnosis.
 

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Yes. But will still having performance issues and gas too.
I want to fix it right. Thanks for the advice.
Are you having issues besides the codes as this clears up the downstream codes and has no effect on performance or gas issues?

Griz
 

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Discussion Starter #9
Due to the code i noticed the power isn't like before. The engine has lost some power and gas mileage got worse...
 

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Due to the code i noticed the power isn't like before. The engine has lost some power and gas mileage got worse...
Might be another problem as lots of folks using headers do this and I've been running them on my 09 5.7L R/T for quite a while and lots of miles with no noticeable change. 25-27 MPG with the MDS working running 70 on the highway.

Griz
 

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Discussion Starter #11
I'm not sure... but I'll get another mechanic diagnosis to see if they can find something else.
 
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