All you need to know about Toyota Oxygen sensors and AF sensors

hello and welcome to the car care nut channel in today's video i'm going to continue my series on how toyota engine controls work today we're going to be covering oxygen sensors and air fuel ratio sensors but before we get started if you're new to the channel welcome consider subscribing check out some of my other videos if you're a returning subscriber thank you so much for watching another one of my videos and without further ado let's dig right into it let's talk about oxygen sensors first this one is as the name says here's an example of an oxygen sensor it's a sensor that measures the amount of oxygen in the exhaust let's talk about that a little bit so you remember in previous videos of this series we talked about a lean condition and a rich condition and how the engine computer is trying to keep the mixture at that perfect square metric whatever word we talked about so the oxygen sensor is another input to the computer to kinda after the whole mess happened the oxygen sensor will tell the computer what happened what's the result of your all the meetings and all the mess that you had to make that stoichiometric so the oxygen sensor will measure oxygen content in the exhaust when you have more oxygen that means that combustion is lean you have less gasoline more oxygen a lot of that oxygen didn't get used in the combustion so it came out of the exhaust if you have a lot less oxygen that means the conditioner is rich that means all the oxygen or a lot more oxygen got used up and more raw fuel came out because the the combustion is rich that's the very basic operation of this or not operation but the idea of this sensor these oxygen sensors they don't work when they're very cold they don't they just don't respond very well so they have a heater built into them and that's about how far we're going to go into their construction so speaking about oxygen sensors let's talk from what really matters in the real world about them their voltage reading these oxygen sensors they they introduce a voltage reading to the engine computer for review if you would remember this is also an input the computer has no way of commanding this sensor to do anything other than just receive the reading that it gives so the sense this sensor ranges from 0.1 volts all the way to 1 volt or actually just under 1 volt 0.9 0.95 very close to 1 volt the middle is the perfect medium when the voltage starts going low we go into the lean side when the voltage rises all the way to 0.9 or closer to 1 volt the computer will understand that we're running too rich and we're going to cover in a little bit in this video towards the end what does that mean for our whole operation but right now let's just focus on the o2 sensor so we understand it now having said that i want to bring it to your attention to one thing with toyota toyota doesn't use only oxygen sensors and you might have heard the term air fuel ratio sensors and people often wonder well what is that this is actually an air fuel ratio sensor in front of me yes i did tell you it's an oxygen sensor because to our eyes when they are sitting next to each other on a table they look identical they have the same number of wires they look the same but they operate completely different which takes us to air fuel ratio sensors people are often confused by them they don't know the difference between it and a regular o2 sensor and let me start from the beginning airfield ratio sensors are used in toyotas for a very long time i don't remember the last toyota that had a regular o2 sensor and you will know to closer to the end of this video we'll talk about where they are positioned and how they're arranged in the car but now let's focus on the air fuel ratio sensor we talked about the o2 sensor low voltage lean high voltage is bridge the airfield ratio sensor it is often called in the aftermarket world wide band o2 sensor and that's basically what it is it just has more range it gives a very much for more precise voltage so the computer can make these micro adjustments not only make big adjustments it can make those micro adjustments and know okay are we rich or lean that's what the ro2 sensor would say but an af sensor would tell it how rich and how lean are we are we just a little bit lean or too much or middle or three quarters or one quarter where are we exactly lean and where are we exactly rich so the voltage reading and this is what matters here we're talking doing this for diagnosis purposes so you guys with diy mechanics and everybody watching this video you'd understand how these cars work because you can't fix these you can't diagnose these if you don't understand how they work so the air fuel ratio sensor normal voltage is around 3.3 volts it can go up to 5 volts it could drop to 0. let's talk about that for a bit so the air fuel ratio sensor up voltages react the opposite of oxygen sensors so the higher the voltage the more lean it is and the lower the voltage the more rich the reading is that's where it gets confusing because they're reversed oxygen sensors are the opposite of air fuel ratio sensors when it comes to voltage reading now the air fuel ratio sensor also has a heater to heat it up make it actually work these sensors don't work they're not very accurate when things are cold they need that heater to heat them up quick so they can start reading so now we understand the difference between an oxygen sensor and the air fuel ratio sensor you just need to understand the voltages and what they mean now airflow ratio sensors anything over 4 volts we're starting to get into a territory that the computer doesn't like anything under two and a half two volts the computer doesn't like that so it needs to stay in within a specific range so keep that in mind when we get to one day get to a video of advanced diagnosis where this will all come into play but for now let's keep things very simple now we know how what the differences are between those two let's talk about how they actually mount in the car and how they're distributed so you will hear the terms bank 1 bank 2 bank 1 sensor 1 bank 1 sensor 2 and all this mess or upstream sensor downstream sensor left and right and and all these confusing terms well let's dig into this and talk about how these sensors are distributed engines have banks they're identified as banks where the control of the computer is divided so in case of a v6 one side of the cylinders three cylinders on one side are bank one and one side is bank two so the engine is split in half typically on all toyota engines four cylinders are one bank the only exception is 2001 to 2005 rav4 it had two banks two four cylinder engine two banks bank one was two cylinders and bank two was two cylinders the most confusing engine to work on because any other engine would be one bank that's a four cylinder but let's let's talk about what makes bank one bank one bank one always contains cylinder number one in the engine whether it's a v8 v6 whatever the case may be bank one contains cylinder one and that actually applies to all cars not just toyotas but we're going to keep a toyota focused here having said that every bank will have two sensors now some cars will have three we'll talk about that in a bit every every bank will have an af sensor and an oxygen sensor the af sensor is directly after the exhaust exits out of the engine out of the exhaust valve into the exhaust manifold sensor is the main input to the computer of what happened in the combustion well i put this much gas we had this much air and i think i got everything right but was it that af sensor tells the computer the gives it like the report card hey buddy here's how you did you did horrible you did great or whatever the case may be the report card of the combustion here's what i see so that is the primary sensor and it is actually a vital sensor to the correct operation in the car and it is directly after the exhaust exits before the catalytic converter or upstream of the catalytic converter so now we know bank one or bank whatever bank sensor one is always the sensor right after the exhaust exits the engine immediately before the catalytic converter upstream of the catalytic converter bank one sensor two is always an oxygen sensor not an af sensor and it is used for a completely different purpose that sensor downstream of the catalytic converter or sensor 2 after the catalytic converter and all that sensor does is give the computer the results again another report card of how the catalog converter is doing we will cover that in depth for the catalog converter in an upcoming episode of this series but for now let's get back to our banks so in a case of a v6 we have bank one sensor one that will be an af sensor on bank one at the top right after the exhaust exit sensor bank two sensor 1 that's on bank 2 on the other bank of the v as soon as exhaust exits bank 1 sensor 2 is behind the catalytic converter after the catalytic converter downstream of the catalytic converter and then same on the other side so that's the basic layout of these oxygen sensors one car that i know of has three a toyota 2002 to 2006 camry 4-cylinder california emissions not all of them some of them will have a third oxygen sensor because it had two cats they needed for some emissions reading for some emission requirement in california we all know california can be special with emissions they had a third sensor to monitor the second catalytic converter that's one unicorn if you would so we're not going to cover too much on that it basically does the same thing we'll cover that more when we talk about catalytic converters so having said all that let's talk about the most important thing with all this mess this is the most important part of this video how does this little sensor is used or its voice is heard by the computer and it makes a significant difference to how the engine runs well when the engine starts cold we all know a reminder you might have heard that engines run rich well the reason for that is cold fuel doesn't ignite as good and it just tends to linger and doesn't really work as much as warm fuel or warm combustion chamber or warm everything for that matter so when the engine starts you're in something called open loop and the loop is the computer listening to the oxygen sensor input when it's open loop it ignores this guy it sometimes even ignores the mass airflow sensor which we talked about in the previous video all it does is it goes by a pre-programmed program that we're going to put this much fuel until the engine reaches this temperature but in reality what it's trying to do is it's trying to give this guy time to warm up so the input from the af sensor air fuel ratio sensor i will abbreviate it as af sensor so the input from the af sensor is accurate and it's trying to warm up the catalytic converter it's trying to warm everything up and you notice toyotas when you start them the rpm will rise and the reason it rises most people wonder why does it why does toyota ride like rise their rpm when they're cold isn't that bad because it's gonna run the engine higher and the oil is trying to circulate well that rise in rpm does so many things first one is it helps circulate that oil faster the second thing and the most important it's trying to warm up the engine the o2 sensor even though it has a the heater is going to still try to blast it as much hot air as possible to warm it up and the most important thing to warm up the catalytic converter catalytic converters don't work very well when they're cold more on that on that episode this the minute this sensor reaches the temperature that the computer is happy with and it now it can the signal is coming out of it is plausible that's another term you will hear it switches to closed loop operation your rpm drops down and that doesn't mean that the engine is fully warmed up to operating temperature no over the years this has been a race between auto manufacturers who can get into close loop the faster the faster you get into closed loop with engine control the better emissions or the less harmful emissions you will get out of the car when it's an open loop operation now there are times while the engine is running it'll go into open loop momentarily and will come back that is normal but for the most time it will try to stay in closed loop operation so let's talk about closed loop here's what happens in closed loop the computer cannot control how much air is coming in because that's based on the mechanical part on your throttle input what it can do though is change the injection volume you remember we talked about fuel injectors it can open that injector for a longer duration more milliseconds equal more fuel sprayed that is can control but how does it know exactly how much to put it's looking at the input from this guy now comes the tango dance if you would here's how the computer is going to have a dance with the air fuel ratio sensor and the injection volume or the direction of the injectors and follow me closely here because this is going to get slightly not simple but complicated the computer will put a specific amount of fuel based on the input that it gets from the mass airflow i have this much air i want to put this much fuel to get to my 14.7 to 1 stykometric that perfect ratio between the two is going to put that in the engine it's going to do the cycle the exhaust comes out this sensor says this sensor just sitting like this very upset too rich you put too much fuel the computer will go in the frenzy no no no let's cut the fuel it's going to cut the fuel keep cutting slowly slowly remember the engine is turning at a high revolution this happens in milliseconds it's going to cut the fuel back just keep cutting the fuel it's waiting for this guy to say yep we're good but guess what this guy never say it's good because that ratio is so such a narrow window that it'll never exactly be there and hold it okay everybody go drink your coffee and we're done no it's gonna say this guy's gonna say their fuel ratio is gonna say too rich the computer will say okay well let's cut the fuel back it cuts the fuel back and then this guy all of a sudden says nope we're too lean now because you cut too much it's going to go okay well let's start adding and then until this cycle keeps going back forth back forth and they just keep chasing themselves after that as you are in your drive-through of mcdonald's getting a dollar menu burger this these guys are doing all this while you're just sitting in your car driving not thinking anything is going on it just keeps adding fuel until this guy says it's too much cuts back add cut back add cut back what it's trying to do is it's swinging back and forth around point the perfect one it can never keep it perfectly there because of the mechanical nature of the engine it's trying to just swing back and forth so here's fourteen point seven two one it's gonna hit it go away hit it come back so when you look at the signal of these o2 sensors you'll see that it's up down up down up down it just keeps going up down up down and the injection volume if you really dig into it it's also doing the same thing it's just going rich lean rich lean rich clean too much fuel too too little fuel too much fuel it just keeps going like that all day long as long as the engine is running it's doing that dance that tango dance back for it back forth so that is essential to your diagnosis because there is a moment when we have problems look when the cars are running great if if your car never has a problem ever why are we having all this why do i have a job and why are you working on your own car at some point something is going to go south and you are greeted by the warmth glow of the second july so i want you to understand the basics let's say you're driving a mouse came under the hood chewed up a vacuum line here's what's going to happen you have a vacuum leak now now the engine is always running lean here's what's going to happen the engine will okay we're getting this much air i put this much fuel the the angry guy the air fuel ratio sensor says nope you're too lean okay well let's add more fuel it's expecting it to say okay now you went too rich so we can go back but we're going we're adding more fuel to compensate for that lean nope this guy says we're still lean keep adding nope we're still lean keep adding nope we're still leaning then the computer says whoa whoa hold on i don't like what's going on here my mass airflow is saying one thing and you're saying something else you guys need to come and have us sit down and let's talk because i don't like what's going on here even though the computer is doing all this dances because of these two guys but he's still the boss he's going to tell them hey guys i don't think you guys are on the same page here stop this whole operation go back to open loop i don't like you guys loose not behind the wheel gets a warm glow of the check engine light that's how this works and it could be the opposite way where you have a leaking injector that's just spraying all the time and same thing the computer cuts back cuts back cuts back and this guy keeps saying we're rich we're rich we're rich and then the computer says okay i don't like this we're going to throw a code so to summarize all this i want you to take the following from this the air fuel ratio sensor it's a viral input to the computer it is basically the report card of how the computer is doing from the other input it gets the stuff from the input from the mass airflow this is how much air we're getting this is how much fuel we're adding but when the air fuel ratio says oh no you're going too rich the computer will react we'll ignore the mass airflow and say yeah you'll be fine let's just cut the fuel a little bit because we're this guy says we're too rich and then all of a sudden this guy says oh we're too lean now okay well let's go the other way just keep back forth back i just want you to visualize that that it's going back forth up down up down all the time because it's trying to keep us in that stoichiometric let's talk about some diy stuff things that you will not find in a book things that i learn as we go and i'm going to share with you did you know that all oxygen sensors are actually 22 millimeter size that to take them off so most people will go oh you need that special socket that has the cutouts or the wire we go through it and this and that and there are cases where you do and some people will say you have to be that cool mechanic that has that special socket even though it's five dollars on amazon but if you have in certain scenarios where the sensor is just sitting there you can take a 22 millimeter wrench put it over the sensor break it loose that as simple as that you don't need any you you're going to use a 22 millimeter wrench on a car on a toyota a lot alignments suspension stuff it's a good wrench size to have especially in an open end and a box in so here is one that will really be useful if you're working with a semi-older car let's say 2000s mid-2000s to late 2000s even into the tent you go to replace an o2 sensor by the way common stuff for toyotas are heater coats the heater just fails what makes these heaters fail usually is if you spray them with brake cleaner for some reason brake cleaner damages the heater in here and the heater is done you get a heater coat you check all your wiring wiring is good you're getting the voltages when you start the car cold but you still have the heater code because the heater is damaged you replace the sensor now you go to take the sensor out and you turn it it turns a little bit then stops it gets real tight you start turning and it's just it's it's a struggle well what happens with these and is common is the threads get locked to the manifold or the exhaust where you're taking them out of here is a trick that you'll never find in any book and actually might not find unless you work at a toyota dealership with older mechanics when this happens to you you loosen and it stops stop right there soak the threads whatever is exposed of the threads with brake fluid not brake clean not pb blaster or some wd-40 whatever brake fluid just soak this guy up and let it sit for five minutes come back in tighten it a little bit and loosen it will come right out now it might come out with like thrash from the old thread on the exhaust you need a thread chaser find the right size if they're everywhere just o2 sensor thread chaser and clean the thread a little bit and install your new sensor all these new sensors when they come in they come with a little cap especially the af sensors they come with a little cap and nic's on them keep that analyses don't take it out because that's why they started doing this older ones didn't have that so they seize up like that and that nics is not any nics do not go using any nics if you take this off for whatever reason use any nics that's a special high temperature nic's leave it on there and the most important thing about diy repairs you will not buy an aftermarket o2 sensor or worse af sensors i have seen so many o2 sensors installed where an af sensor should be folks these these don't work the same they look the same and just because it fits it doesn't mean it ships that's not how this works whatever sensor you get that comes with four wires hanging off of it and you make your own fit your own fits every single car that's the one that doesn't work it needs to be designed for this car and especially af sensors o2 sensors a lot more forgiving af sensors always buy the original or buy a denzo a known brand but always have a way back because you it's very common that i see that you install this aftermarket sensor or whatever you got it it doesn't work flat out of the box not because it's a bad part but because it's not for this car just thought you'd need to know this and don't forget the brake fluid trick and i will cover a lot more in-depth diagnosis and tricks and tips and all this stuff in an upcoming video which we will cover advanced diagnosis so having said all that in the following video of this series we're going to stop learning and we're going to go into a different mode of learning we're actually going to be looking at live data on the car so we talked about all these different sensors and how they're reacting how they're doing everything now the next video we're going to take a step back and get a car we're going to look at some data live data through a scan tool so we can so you can see with your own eyes how these sensors are reacting and then i will create some problems or start changing things and i want you to see rich and lean how the computer reacts and how it starts adjusting things until we get to that video i hope you like this one i hope you learned something new if you did consider giving a thumbs up if you're not a subscriber consider subscribing to the channel check out some of my other videos and until the next part of this series may the lord bless you and keep you and you have a wonderful day

Channel: The Car Care Nut

Views: 94,117

Keywords: all you need to know about toyota oxygen sensors, oxygen sensor explained, air fuel ratio sensor explained, toyota oxygen sensor, how to test o2 sensor, how to test af sensor, o2 sensor tips and tricks, o2 sensor readings explained, how o2 sensor works, how af sensor works, seized o2 sensor, how engine control work, how engine control unit works, toyota engine computer, toyota technology, toyota obd2, toyota catalytic converter, how to diagnose cars, how to fix oxygen sensor

Id: eiY1fHcDqu0

Length: 26min 57sec (1617 seconds)

Published: Sat Feb 27 2021