P0420 infiniti code

How to diagnose code P0420 on a Infiniti QX80. Typically, you'll find out about P0420 because your malfunction indicator lamp or "check engine light" turned on & you or a mechanic diagnosed the problem with an OBD II code scanner like this one from Bluedriver. You may experience a very slight reduction in engine power from reduced exhaust flow ...

Our in-house experts dive into this OBD code issue so that you can best address the problem. Car Values. Price New/Used; ... P0420 - Catalyst System Efficiency Below Threshold Bank 1.A P0420 code is set when the upstream sensor and the downstream oxygen sensor sense the catalytic converter is not doing its job. Basically, the amount of oxygen going into the converter is not being burned, and it detects it through the downstream sensor. Oxygen is the key here. Modern Engine Management Systems leave a little bit of extra ...When the P0133 code is set, it means that the O2 sensor isn’t altering the voltage output as it should when the air-fuel ratio changes. For that reason, it’s categorized as having a slower response than normal. This code indicates trouble with oxygen sensor #1 on bank #1, which is on the same side of the engine as cylinder #1.The code is logged once a potential airflow issue is detected in the secondary air system. The P0411 code will cause engine performance problems like rough running and lack of acceleration. It can also cause backfiring. It can also cause a rich running condition that can cause poor fuel economy and a noticeable rotten egg smell.Code P0420 means "Catalyst system efficiency below threshold (Bank 1)." Driving long-term with this code can cause engine and exhaust system damage. The most common cause of P0420 is a bad catalytic converter, but it can also be caused by other issues, such as a faulty oxygen sensor, a rich or lean running condition, or misfires.Code Tech Notes. As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be ...scr38. 5213 posts · Joined 2004. #2 · Dec 5, 2016. Right primary cat or O2 sensor is bad. The cat is part of the manifold assembly, and is very expensive to change. Check the sensor first. You could switch the right and left O2 sensors Get the code cleared; if the 430 code comes back you have a bad right cat, if you get a 420 code the sensor ...

Re: 08 G35X P0420 cat low efficiency. Post by Piotr93 » Wed Jun 15, 2016 1:49 pm. audtatious wrote: First thing to do is make sure you do not have an exhaust leak which could trigger this code. For HFC's I'm running Invidia on my coupe and it's been issue-free for 6+ years. I've heard good things about Kinetix and a lot of people run Berk.We would like to show you a description here but the site won't allow us.The P0420 code in Ford Focus specifically relates to the Bank 1 catalytic converter, which is the one located before the engine’s cylinder head. ... Revamping INFINITI FX37: Airbag Control Module Replacement Guide. 2009 GMC Yukon XL 1500: Addressing Problems and Complaints.Top 4 Reasons Why You Replaced O2 Sensor and Still Have Code. The most common codes that people will see in this particular situation are P0134, 0138, and 0139, though you are probably seeing P0420. These codes do not point out to a specific issue but they can help hint at the root cause of the issue. Here are a couple of the parts to take a ...Home Forums > Infiniti QX70 FX Forums > FX Forums (2003-2008) > FX (03-08) - Engine & Drivetrain > FX35 OBD code P0037 - Oxygen Sensor Discussion in 'FX (03-08) - Engine & Drivetrain' started by FoX35, Jul 20, 2012. Jul 20 ... Now, I'm getting code P0037 - which I know can be a few things related to the O2 sensors. ...If the efficiency is lower than it should be, the ECU will store OBD-II code P0420. The definition of the OBD-II P0420 code is " Catalyst System Efficiency Below Threshold (Bank 1) ". When the ECU stores this code, it means that the catalytic converter is not operating at maximum efficiency and may need replacement. Car fault code: P0420.Le code défaut P0420 est enclenché en cas de dysfonctionnement d’un ou plusieurs composants du pot catalytique. Cela peut comprendre : un défaut sur un ou plusieurs …Re: 2008 Infiniti G35 Sport Fault Codes. Post by audtatious » Thu May 29, 2014 7:58 pm. The C* codes are related to tire pressure sensors. The others _could_ be triggered from an electrical issue I guess. Have the owner fix the charging issue, clear the codes, see if the come back.

MIL “ON” with DTC P0420 and/or P0430. A. 1. 2. IM. You MUST closely follow the . entire. SERVICE PROCEDURE as it contains information that is essential to . successfully completing this repair. Infiniti Bulletins are intended for use by qualified technicians, not 'do-it-yourselfers'. Qualified technicians are properly trained Infiniti. Code: P0420. Definition: Catalyst System Efficiency Below Threshhold (Includes Hybrid Models) Description: HYBRID MODELS CAUTION: Hybrid systems use very high-voltage battery systems. Before starting any service work involving the battery system, turn the ignition switch OFF and then remove the service plug from pocket in the trunk ... Published: Jan 22, 2010. Before replacing an OBD II converter, always check the diagnostic memory for converter-related DTCs, such as a P0420. Also, make sure that the vehicle has exceeded its emissions warranty. If not, the vehicle must be referred to the closest dealership for warranty services. OBD II monitors include the catalyst heater ...1999 to 2016 Super Duty - BOTH P0420 AND P0430 CODES - Hello all. I'm a new member. I just purchased a 2006 f-250 4x4 extended cab with a 5.4 triton. I bought this truck from the chicago area which is about 175 mile north of my home. After I bought the truck I got about 100 miles down the road and the check engine...

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The Infiniti Mechanic will be able to provide you with the specific O2 sensors that may need to be replaced to address these codes in your 2013 QX 56 4WD. Have you noticed any other issues or issues with your vehicle besides the check engine light and the P0430 and P0420 codes? No. It is a daily driver and still runs fine.2012 infiniti qx56, getting codes p0174 p0420 p0430. Check engine light, runs rough, rough idle, loss of power, limp mode? ...P0420 is a diagnostic trouble code (DTC) for "Catalyst System Efficiency Below Threshold (Bank 1)". 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 ...The cost to diagnose the P0420 2005 Nissan Pathfinder code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type.The P0150 code is triggered when the Engine Control Module (ECM) fails to properly detect activity from the O2 sensor. The O2 sensor transmits a voltage in relation to the amount of oxygen in the exhaust. This voltage is indicated by a value typically between .1 to .9 volts. The value of .1 means the engine is "running lean" and has too ...

The Marvel film will surpass the billion dollar marker 11 days after its release and faster than any movie in history. By clicking "TRY IT", I agree to receive newsletters and prom...16K subscribers in the G37 community. All about Infiniti's G37Code p0420. Just purchase the vehicle 240 miles ago with 135751 miles on it. Seems very suspicious, P0420. I have not - Answered by a verified Infiniti Mechanic. We use cookies to give you the best possible experience on our website. ... I recently got two codes on my infiniti. P0420 and P0430. I.So here is the deal. I get a CES every now and then with a P0420, the catalytic converter inefficient. Truck drives fine no even a burp. So I clear the code ( i know its not a fix lol). Drive about 400 to 1000 and it comes up again. Still no issues. Clear the code (see above). Within the last 10,000 miles 3 times with a code.Code P0420. Post by jsando2 » Sun Oct 17, 2021 7:38 pm. Okay! I replaced all my (4) upstream downstream 02 sensors, both catalysts converters, spark plugs, three coil packs all the exhaust is new and Im still getting Code P0420. Also Im getting the code for the fuel sensor but here is where my question comes into place. I’ve cured many a car with P0420 and P0430 with a tune up. Sometimes it has been spark plug coils which gets a little more expensive, but new spark plugs is the best place to start. The list of things that can cause P0420 to become active is everything from a dirty MAF sensor to an exhaust leak and everything in between. The Galaxy S8 isn’t just a gorgeous Samsung phone — it’s the best-looking phone ever built. Most of that is because of the curved display, which covers over 80% of the phone’s face...Home Forums > Infiniti QX70 FX Forums > FX Forums (2003-2008) > FX (03-08) - Engine & Drivetrain > FX35 OBD code P0037 - Oxygen Sensor Discussion in 'FX (03-08) - Engine & Drivetrain' started by FoX35, Jul 20, 2012. Jul 20 ... Now, I'm getting code P0037 - which I know can be a few things related to the O2 sensors. ...The cost to diagnose the P0420 2007 Nissan Maxima code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type.

Detailed information on the P0420 dtc trouble code. Includes why it happens and how to fix your car. Trouble Code - P0420 Catalyst System Efficiency Below Threshold (Bank 1) ... 1999 INFINITI QX4 (SUV) I have a 1999 Infiniti QX4,engine light on,overall test result:failed and shows codes P0420 and P0430 Catalyst System Efficienc,Bellow …

Code P0420 2006 Toyota Prius Tech Notes. As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the ...Jun 23, 2022 · Check Engine Light and P0420 and P0430 Codes. So, your Check Engine light is on, and you’ve got either a P0420 or P0430 code, on your OBD-II scanner. This “Catalyst system efficiency below threshold” code is triggered when your car’s computer (the powertrain or engine control module (PCM or ECM)) detects a catalytic converter issue. 1A ... Common Reason: Code P0420 is often related to a bad catalytic converter. P0420 means the catalytic converter is not efficiently removing pollutants from the exhaust. Your car won't pass an emissions test. A bad catalytic converter isn't a hazard to the driver but it can overheat and destroy engine components.The cost to diagnose the P0420 2006 Infiniti G35 code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto …Demi Adejuyigbe has written for The Good Place and James Corden, co-hosted the podcasts Punch Up the Jam and Gilmore Guys, and turned the 21st of September into an internet holiday...primoV8. 2029 posts · Joined 2006. #4 · Oct 18, 2022. This particular P0420 DTC is a headache for the first gen trucks. It can be an exhaust leak from either the manifold gasket or the notorious cracked manifold (s). It could also be the catalyst materials inside the cat-converter are no longer doing its job but either way, it requires ...For MORE great Auto Repair Videos, visit us at www.OnlineAutoRepairVideos.com Video on diagnosing and explaining dtc p0430, catalyst efficiency below thresho...A code P0430 Infiniti may mean that one or more of the following has happened: The catalytic converter is no longer functioning properly An oxygen sensor is not reading (functioning) properly There is an exhaust leak ... Related Codes. P0420 Infiniti P0421 Infiniti P0422 Infiniti P0423 Infiniti P0424 Infiniti P0425 Infiniti P0426 Infiniti P0427 ...This mansion Ubud Airbnb has infinity pools, a formal dining room, and sleeps 16,. Perfect for a group of friends or a large family. In Bali, the town of Ubud is known as the islan...P0420. So I’m getting the code P0420 and this is coming maybe two weeks after a new exhaust. The code reads catalyst bank system which usually means that something is wrong with the cats, but I also replaced my cats to brand new high flows a few months back. Anyone have experience with this code after HFC. 2.

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Tech Notes. As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be ...Understanding the P0420 OBD2 Code: What Does It Mean? A Deep Dive into OBD-II Codes. OBD-II codes are a unified diagnostic system that is used in all cars made in the United States after 1996. Before the OBD system attempts were to make car diagnostics easy, but only after this system came to life, did it become possible.What is the Cost to Diagnose the Code P0420 2004 Infiniti G35? Labor: 1.0. The cost to diagnose the P0420 2004 Infiniti G35 code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type.Common Causes of the P0420 Code. There are several common causes for the P0420 code in a Dodge Caravan. These include a faulty catalytic converter, oxygen sensor malfunction, exhaust leaks, and engine misfires. One of the most common causes is a failing catalytic converter due to age, wear and tear, or contamination from oil or coolant leaks.Post by VStar650CL » Wed Oct 11, 2023 8:14 pm. P0420 with A/F or HO2S codes is a different story than P0420 by itself. With no other codes, P0420 practically always means a dying cat. However, most ECM's (including most Nissans) cross-check the wideband sensors in front against the HO2S's in the rear.The P0150 code is triggered when the Engine Control Module (ECM) fails to properly detect activity from the O2 sensor. The O2 sensor transmits a voltage in relation to the amount of oxygen in the exhaust. This voltage is indicated by a value typically between .1 to .9 volts. The value of .1 means the engine is "running lean" and has too ...Interpreting the P0420 Code. If the O2 sensors detect similar results, then something is not right. The values of oxygen have to be different upstream and downstream from the converter. If not, the O2 sensor sends this information to the ECU, which signals the P0420 code. Common Symptoms of a P0420 CodeA P2A00 code means that the powertrain control module (PCM) has detected a voltage reading from the oxygen (O2) sensor for engine bank 1 that is outside of normal parameters. “Sensor 1” denotes a sensor located before the catalytic converter in the exhaust stream, and “Bank 1” refers to the engine bank on a V-style engine that contains ...P0420 NISSAN - Catalyst System Efficiency Below Threshold Bank 1; P0430 NISSAN - Catalyst System Efficiency Below Threshold Bank 2; The Fix. You can eliminate the codes by using a spark plug non-fouler which tricks your engine computer to think that everything is working fine.scr38. 5212 posts · Joined 2004. #2 · Jan 22, 2011. Codes 420 and 430 are low catalyst efficiency. This is usually a sign that the converters that are welded to the manifolds are going bad, the O2 sensors are bad or cracked exhaust manifolds. t. These items are covered by the 8 year/80,000 mile emissions warranty. ….

The P0420 code (Catalyst System Efficiency Below Threshold (Bank 1)) means that the ECU has detected that the catalytic converter downstream of the first bank of cylinders is underperforming. In cars with two cylinder banks (V6, V8), the P0420 code refers to the bank with the first cylinder. An inline-six engine will use this code for the first ...30 Oct 2016 ... We have a good lesson here in this video to not automatically condemn the catalytic converter(s) when you get that dreaded Catalyst ...Apache/2.4 Server at autocodes.com Port 80=====Claim your FREE engine code eraser 👉 https://free.nonda.co 👈=====Engine Code P0420 Saving Repair Parts:C...To diagnose the P0300 Infiniti code, it typically requires 1.0 hour of labor. The specific diagnosis time and labor rates at auto repair shops can differ based on factors such as the location, make and model of the vehicle, and even the engine type. It is common for most auto repair shops to charge between $75 and $150 per hour.Nissanclub.com Nissan - Infiniti Enthusiast Forums. NISSAN ALTIMA FORUMS. 2007-2012 Nissan Altima Discussion (2.5 & 3.5) 2010 Nissan Altima coupe 2.5s/ P0420 ... My code says P0420 Catalytic converter system, bank 1-efficiency below threshold. Catalytic converter, wiring, H02S 2The P0057 code is set when the ECM detects that the HO2S2 on bank 2 has a malfunctioning heater element. The heater in the oxygen sensor helps get the sensor up to operating temperature faster in order to improve fuel economy and emissions. This O2 sensor is located after the catalytic converter and monitors the catalytic converter's efficiency. What is the Cost to Diagnose the Code P0420 2004 Infiniti G35? Labor: 1.0. The cost to diagnose the P0420 2004 Infiniti G35 code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. P0420 infiniti code, Q: Codes P0420 and P0171 appearing. I took my car to the dealership to have it checked out. Two codes were found: PO420 and PO171. They told me that the P0420 is a problem with the actuator (part number 17230-21010), and the 2nd one has to do with the Mass Air Flow (22204-21010). Both of these makes my check engine light continually appear and ..., P0420: Catalyst Efficiency Below Threshold. Related Vehicles: 2012-2018 Veloster 1.6L GDI. Notes/Hints: Check the downstream O2 sensor. If the sensors signal is dropping when it shouldn't, or reading low voltage during WOT, replace it first, clear code (s) and recheck before condemning the catalytic converter., 2011 - 2012 QX56; MIL "ON" WITH DTC P0420 AND/OR P0430 . APPLIED VEHICLES: 2011 - 2012 QX56 (Z62) IF. YOU CONFIRM (Three Way Catalyst Function), CTION: ... Infiniti Bulletins are intended for use by qualified technicians, not 'do-it-yourselfers'. ... Do NOT claim any Diagnostic Op Codes with this claim., P0300 Infiniti Code - Cylinder Misfire Detected Random Cylinders - Code Popularity: 98,733 Views - Repair Importance Level: 3/3 - Repair Difficulty Level: 3/3. Table of contents. Created and updated by William Orellana on Jul 20, 2022. Possible Causes; Tech Notes;, A place for Infiniti owners and fans to hang out and chat about the cars, brand, modding, and more. Similar Nissan cars, like the 350z, 370z, Skyline, etc, are welcome here ... the latest is the check engine light showing up for something in the cats. Has anybody had p0420 and p0320 codes show up? How did you solve this? Also any ..., Nissanclub.com Nissan - Infiniti Enthusiast Forums. NISSAN ALTIMA FORUMS. Engine Performance (2002-2006) P0420 code on 03 Altima 3.5 118k miles. Jump to Latest Follow 15K ... SES light came on yesterday - drove straight to Auto Zone and got the P0420 code printout. I've spent a few hours searching the forums and have a couple of questions for ..., 3. Test for exhaust leaks: Conduct a thorough examination of the exhaust system for any leaks before the catalytic converter. See also Acura RSX: Unveiling All Answers in Q&A. 4. Check for software updates: Sometimes, a software update from the manufacturer can resolve false P0420 code readings., Tech Notes. As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be ..., The P0404 diagnostic trouble code means that the Exhaust Gas Recirculation Circuit Range/Performance fault has occurred. This generic trouble code comes from the powertrain control module ( PCM) and indicates that the Exhaust Gas Recirculation (EGR) valve is not functioning correctly. Normally, this code indicates that the parameters aren't ..., What are the Common Symptoms of the P0420 Code? Illuminated check engine light; Failed emissions test; Rotten egg smell from the exhaust pipe; Reduced …, What Does Code P0430 Mean? P0430 definition: Catalyst system efficiency below threshold (Bank 2).; Issue Severity: MODERATE– Extended driving with this code can cause internal engine damage. Repair Urgency: Get this code fixed as soon as possible. Diagnosis: It is important to complete the entire diagnostic process when …, Infiniti G35 P0420 P0430. Hello mechanics, yesterday I was driving my month-old 196k mile 2005 G35 down the freeway when my Money Light came on. I parked at the nearest sketch gas station and pulled the pending codes using my scanner and got P0420 and P0430, and checked the stored codes to find that only P0420 came up., Image Credits: Mighty Bear Games The runaway success of Axie Infinity and StepN has convinced a flurry of entrepreneurs that web3 gaming, where the ownership of in-game assets is i..., The Golden Girls will set sail in February 2020 on the Celebrity Infinity on a special cruise themed entirely around the iconic television show. The TV show that won four Golden Gl..., There are several potential causes of a P0420 fault code, including: Oxygen sensor issues: A faulty oxygen sensor can cause incorrect readings and trigger a P0420 code. This can happen if the oxygen sensor is dirty or contaminated or if it's simply worn out. Failed catalytic converter: This is the most common cause of a P0420 code., This defouler is not a permanent solution, but it successfully stops the check engine light without having to manually erase codes., Sometimes I allow myself to have full-blown, elaborate fantasies about resort vacations. I’M A LITTLE STUBBORN about roughing it. I have friends who can’t comprehend my willingness..., The fix is quite simple: Trick the ECU into thinking everything is normal with the cat.Engine Code Background:The P0420 code "Catalyst System (bank 1) Efficiency Below Threshold" basically means the front O2 and rear O2 sensors readings are similar, which is bad. Why? Because the catalytic converter is supposed to change the exhaust gases., To diagnose and troubleshoot code P0420 in a Honda CRV, follow these steps: 1. Check for other fault codes: Before focusing solely on the catalytic converter, ensure there are no additional fault codes related to the oxygen sensors, fuel system, or engine misfire. See also Unlocking Your Ford's Door: The Essential Door Code Card Guide. 2., 2012 infiniti qx56, getting codes p0174 p0420 p0430. Check engine light, runs rough, rough idle, loss of power, limp mode? Mechanic's Assistant: That code indicates a problem with the catalytic converter Is the check engine light blinking or flashing, or is it solid? When did you first notice it? Solid., Code Tech Notes. As the code description implies, the P0420 code means that the vehicle's Powertrain Control Module (PCM) has detected that the Three-way Catalyst Converter is not working properly (it is not as efficient as the factory expects). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases, the Three-way ..., P0420: Catalyst Efficiency Below Threshold. Related Vehicles: 2012-2018 Veloster 1.6L GDI. Notes/Hints: Check the downstream O2 sensor. If the sensors signal is dropping when it shouldn't, or reading low voltage during WOT, replace it first, clear code (s) and recheck before condemning the catalytic converter., Engine-Codes.com, Here's a good P0420 diagnostic order for the Mitsubishi Outlander: 1. Check for Other Codes. The first thing you want to do when trying to fix P0420 in the Outlander is to verify there aren't any other trouble codes. Three types of codes can give clues as to what's going on with your vehicle. Misfire Codes., How to diagnose code P0420 on a Infiniti QX50. Typically, you'll find out about P0420 because your malfunction indicator lamp or "check engine light" turned on & you or a mechanic diagnosed the problem with an OBD II code scanner like this one from Bluedriver. You may experience a very slight reduction in engine power from reduced exhaust flow ..., The most common fix for P0420 in the Jeep Patriot is a new catalytic converter, followed by an O2 sensor replacement. Before taking your Patriot into an exhaust shop for an (expensive) new catalytic converter, let's ensure that's what you need. Here's a good P0420 diagnostic order for the Jeep Patriot: 1. Check for Other Codes., Code Number Code Description Related Codes; P0420: Catalyst System Efficiency Below Threshold (Bank 1) P0430 - Catalyst System Efficiency Below Threshold (Bank 2), Nissanclub.com Nissan - Infiniti Enthusiast Forums. NISSAN SENTRA / 200SX / SE-R FORUMS. B15 2000-2006 Nissan Sentra Discussion (SE-R / Spe ... Yeah I know offhand P0420 is cat code, prob broken down so that's why o2 isn't reading correctly since cat isn't doing the job., So I bought an analyser and retrieved a code P0420. Light is now extinguished. Altima, 2005, 2.5 Catalytic converter/exhaust manifold? Right? ... New car: 2010 Infiniti G37S Sedan 6MT Tein-S lowering springs, Taketa Cold Air Intake, Invidia Q300 Catback, slotted rotors, 20" STR Racing 607 20x9 F/20x10.5 R., What is the Cost to Diagnose the Code P0420 2003 Infiniti G35? Labor: 1.0. To diagnose the P0420 2003 Infiniti G35 code, it typically requires 1.0 hour of labor. The specific diagnosis time and labor rates at auto repair shops can differ based on factors such as the location, make and model of the vehicle, and even the engine type., I had my solenoid valve and my BC manifold cat, as well as. I had my solenoid valve and my BC manifold cat, as well as my Gasket-man exhaust five days ago. The check engine light is back on and my. Anthony. High school. 600 satisfied customers. Multiple codes p0430. P0420. P0300., Code P0420 2009 Nissan Sentra Tech Notes. As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the ..., Code P0420 2007 Toyota Camry Description. The ECM uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency. The first sensor, the Air-Fuel Ratio (A/F) sensor, sends pre-catalyst information to the ECM. The second sensor, the Heated Oxygen (HO2) sensor, sends post-catalyst information to the ECM.