Wideband O2 sensors, Narrowband O2 sensors and Fuel trim.

[Music] hi everybody and welcome to new episode of diagnosed Dan today we're working on his BMW 330i an e 91 model Wynnum m-52 engine it was brought in from another shop who tried to diagnose it tried to fix it they threw some parts at it I'm not sure what parts well I know for sure it changed out the mass airflow sensor but it didn't fix the car so in the end they caught me and asked me dan are you willing to take a look and of course we will it came with some paperwork from the other shop and they scanned for trouble codes and it actually has a misfire on cylinder number one a misfire on cylinder number two a misfire on cylinder number three and it has a link code for bank 1 downstream o2 sensor this being a 600 in the car the first three cylinders are Bank one and I actually diagnosed this car this afternoon and it has a bet wideband Bank 102 sensor causing a lean condition in the first three cylinders which is causing the misfires basically well I know a lot of you guys are having trouble diagnosing a wideband o2 sensor while it's no more difficult really than a narrow band o2 sensor so I want to take you guys through the steps of diagnosing a wideband o2 sensor and in the meanwhile let's talk about wideband sensors narrowband sensors few trim and their relation now the first sensor I want to talk about is the narrow band o2 sensor to diagnose the sensor we look at the voltage of the signal wire which runs from zero to one volt now when the voltage is high the sensor is reading a rich condition and when the voltage is low the sensor is reading a lean condition this line in the middle is lept that one or a perfect at a few ratio of fourteen point seven to one everything on this side is red and everything on the other side is a lean condition now we call it a narrow band o2 sensor because the sensor can only read at a few ratios from eleven point eight to one up until seventeen point six to one now when we look at the wideband o2 sensor we don't look for voltage on a signal wire but we look for current being measured in milliamps now when there is no current flow there is a perfect air-to-fuel ratio of 14 point 7 to 1 or lambda 1 when there is a negative current flow the sensor is detecting a rich condition and when there is a positive current flow the sensor is detecting a lean condition now you can measure this with a scope but you can also find this in your scan data now the other thing you can find in the scan data is the leptin number for the wideband o2 sensor which makes it very easy to see if it's reading lean or rich now we call it a wideband o2 sensor because the sensor can read a few ratios from five to one up until 20 to one now let's take a look at the fuel trims fuel trims are measured in a percentage it can go negative and positive now let's imagine our o2 sensor is reading a rich condition in this case a fuel trim will go negative by taking away fuel and shortening the period the injector is open and it will try to force the mixture back to the perfect lab that one now let's imagine we've got a lean condition the fuel trim will go positive by adding fuel by opening the injector longer and it will try to force the mixture back to the perfect lab the one now I don't know if the cameras picking this up but the car is running right now and is stalling and backfiring which is very typical for a lean condition now let's take a look at the scan data and let's start with the fuel trims let's take a look at the fuel trims long term and short term I'm back to not a lot going on over there perfectly normal but let's take a look at bank one long term and short term going way negative minus 30 you saw that guys now let's take a look at the board way negative is over here so that would indicate the o2 sensor is reading a rich condition and a fuel trim is compensating for it now the few trips unbent to were perfectly normal but remember with misfires until in the one two and three which are in bank one that a few trips on bank one were way negative so the computer thinks there is a rich condition inside those cylinders and trying to compensate for it but taking away fuel now also remember when a leak code for our downstream Bank 102 sensor which is a normal narrowband sensor so if we want to check it we should look at the voltage so let's compare the downstream put two sensors a big one and bank two now let's take a look at the live bullets of our downstream Oh two sensors these are narrow band o2 sensors so we're looking at a voltage and bank two completely normal but look at bank one very close to zero so that would indicate a lean condition and let's take a look at our board and on our board close to zero bulb means a lean condition now we've got a link o for a downstream co2 sensor on bank one in this detonator we saw that the voltage on the sensor was very very low indicating we've got a lean condition but is the condition really lean or have we got a bet o2 sensor now let's find that by driving the mixture rich by putting some brick lane inside intake manifold and see how the sensor responds now you guys what's the voltage of this downstream no two sensor while I sprayed some braking into the intake and drive the system rich now what we're trying to prove here is this sensor being okay by the voltage going up when the system goes rich so spring some brake clean into the intake right now [Music] [Applause] and actually the engine starts to run better and watch the voltage of the downstream Oh too and we actually drove it rich we saw the voltage coming up so this sensor is confirmed it is okay now we actually confirmed the down stream up to sensor of bank 1 working just fine there is actually a leap condition inside those cylinders now if the data stream of two sensor is seeing it the upstream wideband o2 sensor should pick it up - what does it let's take a look looking at the live data of our upstream bank 102 sensor this data is always available in your scan - in generic mode in OVD mode the upper number being the lepton number which is smaller than 1 indicating a rich mixture which we know is not true the number in the bottom is the current flowing through the signal wire of our upstream o2 sensor and milliamps we see this is negative indicating as we have learned a rich mixture which we know is not true this sensor is not telling us the truth guys and we need to replace it now the downstream o2 sensor of bank 1 being a narrow band o2 sensor showed a very very low voltage indicating a lean mixture and we tested it in fact it was a lean mixture the sensor was right but why was the mixture so lean well the upstream wideband o2 sensor was showing us a negative current indicating a rich condition and the fuel trim was responding by going way negative and taking away the excess fuel but in fact the mixture was never rich and it was only driving the mixture more and more lean causing the engine to stall and to misfire on bank 1 now I'm going to replace this upstream bank 102 sensor for a brand new one now after I did it let's see what changed on bank wants future in the downstream Oh to sensor voltage and the upstream up to sensor current the upstream o2 sensor our wideband sensor for bank 1 replaced now let's take a look at the scan data the one on top a short term fuel trim the second a long term fuel trim all normal the third our downstream o2 sensor voltage no longer lean the next to let that number for the o2 sensor all normal and the last being the current flow of our upstream o to sensor switching from positive to negative again diagnosing o2 sensors is easy right well at least nowadays we are looking at narrow band o2 sensors DISA look at the voltage when the voltage is low the system is lean when the fault is high the system is rich when you're looking at wideband o2 sensors just look at the current flow when the current flow is negative the system was rich and the current flow is positive the system is lean if you want to remember this just think about few trims when the fuel trims are negative you're taking away fuel because the system was rich when the current flow is negative the system is also rich now if the current flow is positive the system is lean if your fuel trim is positive you're adding fuel because the system was lean now if you liked this video and if you want to learn more please subscribe to my channel you will get a notification each time I post a new video and diagnose then fixed it again a little bonus material for you guys I want to prove to you guys you cannot drive the system lean by creating a vacuum leak inside this intake manifold of this BMW there's no vacuum I'm gonna prove it by removing the map sensor and there is some airflow but no vacuum is one of you guys no sinuses please explain it to the rest in the comment section below see you next time guys [Music]

Channel: DiagnoseDan

Views: 145,535

Rating: 4.9707551 out of 5

Keywords: A/f ratio, educational, diagnosedan, fuel trim, explained, bmw, Wideband O2 sensor, Air/fuel ratio, gmto, lambda, A/f sensor, O2 sensor, diagnose, Premiere_Elements_15, gmto scope, narrowband O2 sensor

Id: Dwij_fuceUo

Length: 13min 52sec (832 seconds)

Published: Mon Feb 19 2018