What the code is telling you is that the catalytic converter has failed an efficiency test. In However, I see questions all the time on auto forums asking if a new oxygen sensor will fix the problem.
The answer is—almost never. Well, kinda. You could just throw a new upstream or downstream oxygen sensor in and see if it works. VE determines how well the engine is breathing. You also need to determine if a misfire caused the cats to go bad so you can fix the underlying problem and not damage the new catalytic converters. This is really simple: misfires kill catalytic converters. So the first thing to check if for current and history misfire codes P through P Locate the parameter I.
If you find misfires, correct the misfire problem before you go any further. Fuel trims is the addition or subtraction of fuel made by the ECM in order to achieve proper emissions. You must check them in all modes of operation. So take the vehicle for a test drive and watch fuel trims when accelerating, cruising, highway speeds and declaration.
So the upstream oxygen sensor will change rapidly from rich to lean. The downstream oxygen sensor, on the other hand, should show very little movement. During a P readiness monitor test, the ECM will purposely and rapidly command a very rich and very lean mixture to force the downstream sensor to read the excess fuel or oxygen. If it sees that behavior, it knows the catalytic converter and the oxygen sensors are operating properly.
The same applies to the upstream sensor. An exhaust system leak really screws up the P testing routing. An exhaust leak near the upstream sensor can cause the downstream sensor to read a steady lean condition. The ECM would interpret that as a bad catalytic converter.
You can add propane fuel to the exhaust to force the reading up to prove that the downstream sensor is good. A properly operating catalytic converter and muffler system and an engine with good fuel trims and no misfires should have good acceleration at wide open throttle. So take the vehicle to a safe area and put the pedal to the metal.
If you notice a lack of performance, you should suspect exhaust obstruction. Starting from a slow roll put the pedal to the metal until the vehicle makes the shift. Then head home and enter the peak values into a volumetric efficiency calculator. Intake air temperature should decrease during acceleration.
An increase in intake air temperature during acceleration is automatically a sign of a plugged catalytic converter or muffler, regardless of the VE calculator results.
Enter the data on a volumetric efficiency calculator like this. A low reading indicates an engine breathing problem.
A P and a breathing problem is a dead ringer for a bad catalytic converter. Unlike the cheaper Haynes and Chilton manuals that cover multiple year models, leaving the exact information you need to fix your car, these professional manuals cover your exact year, make, model.
Plus, they contain full trouble code descriptions and troubleshooting instructions. Pricing: Eautorepair.Repair Information for P Honda code. Verify that the fuel trims on both banks are good at idle and when driving the vehicle. If the rear O2 sensor is switching rich to lean, the catalytic converter is not storing oxygen correctly. When the catalytic converter functions correctly, the rear O2 sensor should not switch.
If the rear O2 sensor switches at a steady cruise while driving, the catalytic converters are failing. On the vehicle in the video, The only reason the cat was replaced on this car was due to rust and it set the p the day after.
And here is the follow-up video to the first on. A complete guide to diagnosing a p on a Honda CRV. CATS have no moving parts and no consumable components, so they should last the life of the vehicle; if a CAT fails there is always some kind of external cause involved. This can be physical damage from an impact or vibration, poisoning with a foreign substance such as fuel system cleaners or oil additives, or from an engine burning oil or coolant.
A very common cause of CAT failure is fuel contamination from a misfire condition or an engine that is constantly running rich; any unburned fuel exiting the engine hits the CAT and burns there, which raises temperatures inside the CAT high enough to melt and damage the internal ceramic honeycomb causing it to crumble apart. This is usually visible if you look inside the old cat when it is removed.
That is probably what is happening in the car in the video. The sensor is alive and operational, when he snaps the throttle open you can see the voltage spike low momentarily from all the extra air entering the engine when the throttle is opened.
That engine is dumping unburned fuel down the exhaust, and that is the likely cause of both of the converter failures although the mechanic in the video does not mention nor check it. Odds are if he installs a third one it too will be back with a P failure in a few weeks. That engine probably has high fuel pressure, a dripping injector, a vacuum leak which drops MAP so the ECM thinks the engine is under loada faulty thermostat causing the engine to run too cold, or an out of calibration intake air temp or coolant temp sensor causing the rich fuel mixture, or engine misfire that is killing the CATs.
Nissan Murano P0420: Catalyst System Efficiency → Below Threshold → Bank 1
From my understanding, they work much differently. If you have any insight on how these work that would be helpful. The only reason the cat was replaced on this car was due to rust and it set the p the day after. So, this is your original content? I was looking at your scan PIDs in the video and noticed that one was front O2 and it was hanging at mv; that must be a calculated value in the scan tool itself then.
It might be interesting to look at the fuel trims to see if the PCM is commanding a lean correction in response to a rich mixture. If your trims are centered then there probably is not a mixture problem, but if fuel trims are maxed out lean I think I would investigate a little to find out why. The output voltage from the sensor varies above and below that median lambda.This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation.
Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. A P code indicates a problem with the catalytic converter. The purpose of the catalytic converter is to break down harmful pollutants created during the combustion cycle. By using fine platinum and gold meshes to filter exhaust fumes, the catalytic converter is able to reduce the emissions expelled from the exhaust pipe.
The catalytic converter has two oxygen sensors. One oxygen sensor is positioned in front upstream of the catalytic converter and the other O2 sensor is positioned at the rear downstream. If the upstream oxygen sensor is working properly, its readings should fluctuate from when the car is at operating temperature and when running in a closed loop.
If the downstream oxygen sensor is working properly, and there isn't an issue with the catalytic converter, its readings should remain steady. When the oxygen sensors have similar readings to each other, it indicates that the catalytic converter is not working as intended. If the voltage of the downstream oxygen sensor decreases and begins to fluctuate like the upstream oxygen sensor, it means the oxygen levels are too high and the Powertrain Control Module PCM will store the P trouble code and turn on the check engine light.
Though there are often no noticeable symptoms of a failure within the catalyst system, including drivability problems, there are 4 common indicators of the P code:. Check Engine Light is on. Many things can trigger the check engine light to turn on.
A mechanic will need to use a diagnostic tool to read the code and pinpoint the exact cause of the problem. Lack of power after vehicle warms up. The engine will not run as well and may not provide enough power for acceleration. Speed of vehicle may not exceed mph. This may cause issues when driving along highways and freeways with higher speed limits, though you may not notice the symptom if you drive slower through mostly-residential areas.
Rotten egg smell coming from the exhaust pipe. This smell occurs from the incorrect amount of oxygen in the catalytic converter, which leads to excess sulfur in the fuel tank, creating the odor from the exhaust system. The most common mistake is replacing the oxygen sensors before completing the diagnostic process. If another component is causing the P trouble code, replacing the oxygen sensors will not fix the problem.
It is common for a driver to experience no driveability problems when the P trouble code is present. Other than the Check Engine Light being on, the symptoms of this trouble code may go unnoticed. However, if the vehicle is left in error without addressing the problem, serious damage could occur to other components.
Because there are no driveability symptoms associated with the P trouble code, it is not considered serious or dangerous to the driver. However, if the code is not addressed in a timely manner, the catalytic converter could be seriously damaged.
Because the catalytic converter is expensive to repair, it is vital the P trouble code is diagnosed and repaired as soon as possible. Problems with the ignition system, fuel system, air intake, and misfires can damage a catalytic converter if they are not addressed quickly.
These components are most the common causes of the P trouble code. When replacing a catalytic converter, is it a good idea to replace it with an OEM unit or an oxygen sensor replacement that is of high quality. It is common for aftermarket oxygen sensors to fail, and when they do, the P trouble code may return again. It is also a good idea to contact the manufacturer to see if your vehicle has a manufacturer warranty on parts that are related to emissions.
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I feel like the misfires are being caused by the corroded rotor but I have no clue about the P Any help would be appreciated. Staff member. Registered VIP. Registered OG.
If you aren't mechanically inclined, I would suggest taking it to a mechanic to diagnos. Once they give you the answer, you can decide weather you want to replace what is wrong. I would NOT suggest throwing parts at it without finding out what is wrong first. The main thing people do with a P code is throw an o2 sensor at the problem which is wasting money if you are unlucky and it doesn't fix it.
Last edited: Jan 31, RonJ Banned. After you do a full ignition system tune up plugs, wires, cap, rotorreset the ECU and run the engine to see whether any codes return. If P returns, you'll need to replace the cat. Can the car start at the moment?
Most times if there are codes for misfire and a P cat code it is most likely due to the cat. Do you currently have any performance or driving issues? Like maybe low power, loss of power, can't get to certain speeds?
If the code P stays on long enough it may cause a clogged cat causing your exhaust system to not be able to get rid of all your exhaust produced from the engine.
It then backfires it into the engine causing those misfires. Easiest thing to determine this is to put a vacuum gauge on the intake manifold and see what kind of vacuums you have at idle and at about rpm or rpm in neutral. If you don't have a vacuum gauge and the car can't start or has very low power to move even with the throttle to the floor, I would remove the front O2 sensor and see if the engine can breathe.
With the O2 out of the way the exhaust can escape and engine will run better. Not like it should but better if the cat is clogged because the opening for the O2 is very small compared to the size of the factory exhaust.I wrote a much more detailed explanation of how an emission system works and what causes these codes.
Read this post and then refer to this more detailed post. The oxygen sensor in front of the catalytic converter switches back and forth between rich and lean as the computer constantly changes air fuel mixture.
P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1)
But after the exhaust leaves the converter, the next oxygen sensor should not switch between rich and lean. If it does, that means the catalytic converter is NOT doing its job and the computer turn on the check engine light and set code P Catalytic converters generally do NOT fail on their own. They usually fail because of misfires that have not been repaired.
That allows the engine to dump excess gas into the converter. The excess gas is burned off in the converter and causes internal core temperature to rise to the point of destroying the converter. All the precious metals melt. If you replace the catalytic converter but do NOT fix the underlying cause, you will be replacing the converter again and again.
Also, if you buy a cheap aftermarket converter, you are fooling yourself. Most of the cheap universal converters are missing Cerium, a metal that stores and releases oxygen. That will cause the converter to malfunction.
Unlike the cheaper Haynes and Chilton manuals that cover multiple year models, leaving the exact information you need to fix your car, these professional manuals cover your exact year, make, model. Plus, they contain full trouble code descriptions and troubleshooting instructions. Pricing: Eautorepair. So you have to refer to the factory legends to learn the identification symbols and then refer back to circuit diagrams to find the splice and ground locations.
However, Alldatadiy. If you need to dig into your doors, dash or console, Alldatadiy. Find this article useful?
Share it! Categories Generic non-manufacturer-specific P code definitions. Tags catalytic converter check engine Code P P Prominent words catalytic catalytic converter code p computer converters detailed engine excess excess gas exhaust means the catalytic means the catalytic converter oxygen oxygen sensor rich and lean sensor system.When attach a trouble code reader and come up with a P, your first assumption may be that you need a new catalytic converter, simply because the words catalytic converter are mentioned in the code.
After the tests you may indeed discover that the catalytic converter is bad. If the readings shows the exhaust is rich, the PCM will cut back on fuel.
That sounds easy, right? If the PCM overshoots and provides too much fuel, that extra fuel gets burned off in the catalytic converter. If the catalytic converter is doing its job properly, the downstream O2 sensor, located AFTER the cat converter, should rarely switch between rich and lean. If it does toggle between rich and lean, the sweep should be fairly mild.
Catalytic converters have a ceramic honeycomb inside and the surfaces contain a coating of precious metals like platinum, Palladium, Rhodium, and other non-precious metals.
Cat Converter showing honeycomb in good condition. However, if too much unburned fuel enters the cat converter, the oxidation process creates too much heat and the converter starts a runaway reaction. If that continues, it causes a meltdown. Melted ceramic honeycomb. This is a destroyed converter caused by ignoring engine problems. Once that happens, the cat converter is toast. Excess fuel, bad valve stem seals that leak oil into the combustion chamber, coolant leaks that send coolant into the exhaust stream—all of those engine problems can kill a cat converter.
So shut up and stop complaining about how you have to buy a scan tool.
P0420 Honda Fit
Depending on your vehicle, you may be able to monitor both short and long-term fuel trim. In an ideal world with a brand new engine, the short term fuel trim should be 0. When the PCM exceeds that, it starts boosting long-term fuel trim, so check both. The number one villain is a vacuum leak after the MAF sensor has measured how much air is coming into the engine. That causes the upstream O2 sensor to see a continually lean exhaust and it adds fuel to compensate.
Plugged fuel injectors, a bad fuel pressure regulator, and a bad fuel pump can also cause a lean condition. If the fuel trims are in the normal range, next check the upstream O2 sensors. A healthy O2 sensor should switch between rich and lean at least times in 10 seconds. That metric actually does the counting for you. Professionals use a scope to check for cross counts. That causes the PCM to react too slowly, forcing the cat converter to see too much fuel, then nothing.
That causes the downstream sensor to switch between rich and lean and cause a P or P code. Ignore the problem and the cat converter WILL go bad from all the extra fuel. So replace the lazy upstream sensors, clear the codes, and complete another drive cycle. Click here to understand drive cycles.Forums New posts Search forums. What's new New posts New profile posts Latest activity.
I keep throwing a P code says "catalyst system efficiency below threshold bank 1" my car hesitates sometimes when shifting its rare though and I read that it could be a bad cat causing the tranny to slip.
I have inspection next month and I need to get rid of the engine light. I tried the 02 sensor spacer on bank 1 not 2 and the light came back on. Im trying to find out a way to not spend money on a new cat. Any suggestions? New sensor? If I were to replace the 02 sensor since the code is saying bank 1, which is the upstream 02 sensor, would it only be that sensor and definitely not bank 2 sensor?
Yes that is how the OB2 identifies one from the other. At this moment i can't remember the location of bank1. I know the 02 sensor thats right after the headers kind of before the cat is for air fuel ration is that the bank 1 sensor? Sorry i cant be of much help at the moment My book is at the house. This might help. XpL0d3r I had a Civic once. Staff member. Registered VIP. Registered OG. The first sensor takes an emissions reading of the exiting exhaust gases.
The gases go through the cat, reducing emissions. Then the secondary sensor reads the gases again to ensure the cat did it's job. If the readings are too similar, P pops up.
It's likely that the issue is with the catalytic convertor.
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