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Discussion Starter #1 (Edited)
i have a 2013 dodge challenger sxt 3.5L v6. about a month ago i installed a borla s type cat back exhaust and a k&n hi flo intake. last week i got the p0420 code. brought it to my mechanic and he cleared it to see if it was a glitch. 4 days later it came back. I don't have any of the original parts to swap out to see if the new parts were the issue. the car only has 35,000 miles on it so i am doubting that it is a bad cat. I talked to a couple of my car buddies and they are all saying that the freedom of air flow from the intake and exhaust could be throwing off the computer and causing it to throw the code. they suggested a tuner would fix the problem. are they right? if so i looked into the diablo i3 and diablo trinity. any suggestions there? looking for some guidance. also wouldn't mind the performance upgrade as well. thanks
 

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I just checked my engine a little. i didn't see any visible issues and i also heard no hissing while idoling. when i started my car rpms were at 1200 than dropped into a true idol at 800 rpms and there was no fluctuation. it was very steady. i know i haven't thoroughly checked for vacuum leaks with smoke or spray but usually fluctuation rpms would be a symptom of a vacuum leak
 

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I just checked my engine a little. i didn't see any visible issues and i also heard no hissing while idoling. when i started my car rpms were at 1200 than dropped into a true idol at 800 rpms and there was no fluctuation. it was very steady. i know i haven't thoroughly checked for vacuum leaks with smoke or spray but usually fluctuation rpms would be a symptom of a vacuum leak
General rule when some error or problem appears out of the blue last thing touched is first thing suspected.

Since you just installed an exhaust, check for exhaust system leaks. Any leak can let in outside air which can affect the O2 sensor reading and trigger a P0420 (or P0430 for the other bank) error code.

While you are there be sure the pre-post converter sensors are properly installed -- you didn't leave one loose -- and the wiring connections are all good.

As an aside: Do not clean 02 sensors. Do not touch the tips. Handle with extreme care. Do no use anti-seize. Do not spray any electrical contact cleaner on the electrical contacts (some sensors "breathe" via the connector and this cleaner can ruin the sensor).

The error code esssentially means the converter is not operating up to a suitable efficiency level. Efficiency is measured/determined by the converter's ability to store oxygen. The converter is unable to store oxygen. If it can't store oxygen it can't retain oxygen to have available to react with the exhaust gases.

The guidelines for dealing with the P0420 (and P0430) error code might be different for a Dodge but my experience with dealing with a P0430 for a few years is if the P0420/P0430 error is accompanied by any oxygen sensor codes or if there are any oxygen sensor code pending to replace the sensors indicated by the code(s) and clear the P0420 error code then road test the car.

If the P0420 (or P0430) code comes back replace the indicated converter.
 

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So actually, one day I parked my car at work and when i was done with the day I came back to my car to drive home and the CEL was off!!!! it has stayed off for 1500 miles now so i'm thinking maybe it was just a glitch? could this be possible
 

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I just checked my engine a little. i didn't see any visible issues and i also heard no hissing while idoling. when i started my car rpms were at 1200 than dropped into a true idol at 800 rpms and there was no fluctuation. it was very steady. i know i haven't thoroughly checked for vacuum leaks with smoke or spray but usually fluctuation rpms would be a symptom of a vacuum leak
General rule when some error or problem appears out of the blue last thing touched is first thing suspected.

Since you just installed an exhaust, check for exhaust system leaks. Any leak can let in outside air which can affect the O2 sensor reading and trigger a P0420 (or P0430 for the other bank) error code.

While you are there be sure the pre-post converter sensors are properly installed -- you didn't leave one loose -- and the wiring connections are all good.

As an aside: Do not clean 02 sensors. Do not touch the tips. Handle with extreme care. Do no use anti-seize. Do not spray any electrical contact cleaner on the electrical contacts (some sensors "breathe" via the connector and this cleaner can ruin the sensor).

The error code esssentially means the converter is not operating up to a suitable efficiency level. Efficiency is measured/determined by the converter's ability to store oxygen. The converter is unable to store oxygen. If it can't store oxygen it can't retain oxygen to have available to react with the exhaust gases.

The guidelines for dealing with the P0420 (and P0430) error code might be different for a Dodge but my experience with dealing with a P0430 for a few years is if the P0420/P0430 error is accompanied by any oxygen sensor codes or if there are any oxygen sensor code pending to replace the sensors indicated by the code(s) and clear the P0420 error code then road test the car.

If the P0420 (or P0430) code comes back replace the indicated converter.
So actually, one day I parked my car at work and when i was done with the day I came back to my car to drive home and the CEL was off!!!! it has stayed off for 1500 miles now so i'm thinking maybe it was just a glitch? could this be possible
 

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Probably not a glitch. The auto maker is on the hook for any converter problems the 1st (IIRC) 8 years, 80K miles, courtesy of the federal emission laws.

The auto maker has a lot riding on what the DME reports regarding converter operation so if anything the glitch filter is going to be pretty strong.

Actually this filtering is partially provided for by it takes some time for the DME to decide the converter is not operating up to efficiency. The DME monitors the exhaust gas content being fed to the converters -- via the #1 sensors (located ahead of the converters) -- and monitors the exhaust gas content coming out of the converters.

At idle about once a second the DME varies the engine fuel/air mixture from a little too rich to a little too lean. As a result the #1 O2 sensor readings show a drop in oxygen content in the exhaust gas then an increase in oxygen content in the exhaust gas.

The #2 sensor readings show this too but the reading swings are not nearly as large.

For instance the #1 sensor voltage readings -- for narrow band sensors -- should range from less than 0.1V (a lot of oxygen) to more than 0.7V (little oxygen).

The #2 sensor voltage readings want to remain in the 0.6V to the 0.7V. This shows little oxygen remaining in the exhaust gas from the converter. Because the DME knows -- from the #1 sensors -- the converters are getting an excess of oxygen this is taken as a sign the oxygen is being consumed in the converter in the processing of the exhaust gases.

If the #2 O2 sensor voltage levels drop this is a sign the converter is letting oxygen pass through and if this continues too long the CEL comes on and the P0420 (or P0430) error code is logged.

You modified the intake and the exhaust. The problem with aftermarket exhaust systems is many fold. Granted this doesn't apply to all of them but to enough of them. The flow of exhaust gas from the exhaust port to/past the #1 sensor then through the converter and then past the #2 sensor is critical. O2 sensors need to be hot to work right (as does the converter). O2 sensor working temperatures can be close to 600C. The #1 sensor wants to be in the direct exhaust gas flow to remain hot. The converter wants to remain hot as well. It gets some heat from the exhaust gas but also some heat is generated from the chemical reactions that take place in the converter as it converters the exhaust gases into less harmful compounds.

This generated heat helps keep the #2 sensor hot.

Besides the exhaust gas flow past the sensors the exhaust gas flow through the converter wants to be evenly distributed and there be enough surface area and proper flow to ensure all the exhaust gases come in contact with the working surfaces of the converter, surfaces that have a very thin coating (just atoms thick) of the catalyst metals: Platinum, palladium and rhodium.

These metals are expensive and the layer is as I said above just atoms thick.

Auto makers spend a lot of time and money to ensure these (and other) important items are taken care of. (Might add here that my info is GM and Chrysler have the rep for the best converters, for being very good with a good coating of catalytic metals.)


The car/engine has to pass strict emissions testing and then in the hands of the customer after a few years in some areas of the country the car/engine is subjected to periodic emissions testing. And the EPA randomly obtains used vehicles to run a thorough battery of emissions tests on used vehicle to ensure compliance even in areas that don't have emissions testing laws. If the EPA found an auto maker's cars doing poorly you can be sure there would be repurcussions.

With a change in the exhaust system you may (may) have replaced a very good exhaust system with one that is not so good.

There is too the issue of the intake changes. The factory air intake system is designed to filter out dirt, avoid water intrusion, to name just a couple of things; but to also ensure the air flow past/through the MAF is laminar. If the air flow is not laminar but turbulent this can affect the MAF's abilty to measure air mass and the info it sends to the DME that the DME uses to calculate the amount of fuel to inject will be wrong.

Converters operate very efficiently but to do so require a very precise air/fuel mixture. The periodic switch from a lean to a rich mixture I spoke of above is in reality very very small.

If the modifed/aftermarket air intake system has negatively affected air flow through the MAF this can cause problems with the converters.

Also, you have to be very careful with cold air intakes. While a big old honking naked air filter visible when one opens the hood looks cool, it may not deliver cool air to the engine. It can deliver under the hood air, hot air, to the engine and this can mess up the fueling.

You really can't tell much about the quality of the aftermarket exhaust system. Assuming it is good you have to be very sure there is no exhaust leak.

At the other end of the engine you have to be sure the air filter, if it is an oiled type, is not over oiled. There are some who claim this can affect the MAF. The air filter maker denies this. All I know is the thin film MAF is designed to be less sensitive to contamination and it is it but it is not totally immune. There is a limit. If you have oiled the filter element to the point that limit has been exceeded...

If you are sure the exhaust system is installed properly with no air leaks and you are likewise confident the air intake system is satisfactory then you may have to have the car "tuned". This involves monitoring various engine telemetry and the exhaust gas contents (with a 4 gas exhaust analyzer) to determine if the change in the intake system and exhaust system requires some compensation/customization to get the most out of the changes and eliminate the CEL.

With the CEL or even with the conditions the pending CEL indicates is occurring, the DME will adjust fueling to try to eliminate the error condition. If the DME can't do this the error code means the auto maker has to replace the conveter under warranty. But the DME adjusting fueling can result in a less than optimum fueling of the engine. While engine damage is unlikely -- but the fueling can get so far afield misfires can occur -- peformance can suffer which is just the wrong way you want to go in this regard.
 
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