Downstream O2 sensor fault (check engine)

[blackmax]

So I go to have my truck smogged today. But the guy said that with the check engine light on.....it will automatically fail. He pulls the code and says it's left side (I think) downstream o2 sensor. I figure, no problem, I'll just get a sensor and install....see you tomorrow. He then told me he thought it would be really, really difficult to DIY....and that I might want to take it to my mechanic.

Is there something about an O2 sensor on the V6 that would be troublesome, in terms of pulling the old one out and screwing the new one in?? Why would he think that it could be hard for a guy with tools to DIY??

Any reason why I can't perform this fix in 10 minutes?? :wtf:

 

[pearlj10]

I did the downstream o2on right side. Piece of cake. Look at rockauto or other online sites for part if you have time. Local parts stores were almost twice as exp??ensive.

 

[pearlj10]

o2

I did the downstream o2on right side. Piece of cake. Look at rockauto or other online sites for part if you have time. Local parts stores were almost twice as expensive.

 

[ronsta]

How many O2 sensors are there on the 4G v6 ?

 

[Belovian]

How many O2 sensors are there on the 4G v6 ?

Either three or four. But 4 I believe. I know the 4.7's have four. One for each bank upstream (before the converters) and one for each bank downstream (after the converters).

If you can find out what the code is it'll tell you which side needs to be changed.

Jess

 

[ronsta]

Thing is im gonna get them all and change them all out, its why i need to know how many..

 

[lilengine]

There is 2 upstream air fuel sensors and 2 down stream o2 sensors.. but be careful just because there is a code for an o2 sensor does not mean that that is the problem. Alot of times the Air fuel sensor will fault causing a false reading on the 02 sensor and setting a check engine light for a o2 sensor. Also dont forget that you cant just clear the light after replacing the part.. You have to let the pcm set the readiness monitors to set..

 

[ronsta]

I'm not getting any CEL, just suspect that the O2 sensors may be the reason why my truck is chugging gas.

The front O2 (upstream) sensors are aka the air/fuel sensor right?

 

[Belovian]

I'm not getting any CEL, just suspect that the O2 sensors may be the reason why my truck is chugging gas.

The front O2 (upstream) sensors are aka the air/fuel sensor right?

Correct the two upstream sensors measure the air/fuel (actually the amount of oxygen in the mixture) coming from the engine before the converters. the 2 downstream sensors also measure oxygen levels in the air stream, the difference is that the downstream sensors are just watchdogs, they're checking both the upstream and the converters, and are not used to adjust fuel mixture.

Although it is "possible" that a faulty upstream could give a bad reading on a downstream, it is very unlikely that it would happen without setting the CEL. More often than not you would come in with several codes. We would erase all and see what resets first to get a place to start.

jesse

 

[ronsta]

Correct the two upstream sensors measure the air/fuel (actually the amount of oxygen in the mixture) coming from the engine before the converters. the 2 downstream sensors also measure oxygen levels in the air stream, the difference is that the downstream sensors are just watchdogs, they're checking both the upstream and the converters, and are not used to adjust fuel mixture.

Although it is "possible" that a faulty upstream could give a bad reading on a downstream, it is very unlikely that it would happen without setting the CEL. More often than not you would come in with several codes. We would erase all and see what resets first to get a place to start.

jesse

I'm not really understanding the autotech lingo but I ordered all 4 sensors. Would it hurt to change them all out? I would love for my mechanic to only change out the ones that need changing but that might take up a lot of his time (no good) and eventually the old ones would need to be changed out too, no?

 

[Belovian]

I'm not really understanding the autotech lingo but I ordered all 4 sensors. Would it hurt to change them all out? I would love for my mechanic to only change out the ones that need changing but that might take up a lot of his time (no good) and eventually the old ones would need to be changed out too, no?

I can't hurt to change them all. However checking them really isn't all that difficult. It usually involves hooking up a scanner and driving around watching O2 data. but again changing them all can only help.

Ronsta, if you can try and get some fuel economy measurements before and after The O2 replacements, it would give us something concrete for other members.

 

[ronsta]

Cool, they're on the way via amazon, great prices. $40 lower (each) for the 2 upstream ones. Hopefully this will fix all our MPG issues. I know a lot of you on here are suffering from bad MPGs, maybe you just don't know it yet just like a certain mechanic I know who i only recently convinced that he has a problem with his 4G 4R. If it's not that hard then I might give it a shot.

I don't have a scanner right now, would the scangauge 2 work?

Best case scenario would be a before picture showing the 320 mile range on a full tank of gas, the after picture would show 400+!!

I seriously hope this is it b/c I plan on driving to Canada soon.

Oh Yea I changed my gas cap last night to one that locks. I changed it mainly b/c i don't hear the hiss anymore so thought that was kinda funny. No immediate results from that yet but it was a cheap test to rule out.

 

[Sungod]

I'm not really understanding the autotech lingo but I ordered all 4 sensors. Would it hurt to change them all out? I would love for my mechanic to only change out the ones that need changing but that might take up a lot of his time (no good) and eventually the old ones would need to be changed out too, no?

That will be expensive if you stick to dealer parts, which you should for sensors. Aftermarket sensors are a huge risk.

From what I have read on the sensor, they are passive and merely sense faults and there are no adjustments made to the fuel mix based off of their sensing. So you are not going to see any kind of improvement in mileage by replacing them.

 

[ronsta]

All Denso right? What part # and how many of each ? Includes air fuel sensor too ?

 

[Belovian]

That will be expensive if you stick to dealer parts, which you should for sensors. Aftermarket sensors are a huge risk.

From what I have read on the sensor, they are passive and merely sense faults and there are no adjustments made to the fuel mix based off of their sensing. So you are not going to see any kind of improvement in mileage by replacing them.

What you read is wrong, or you misread. The upstream O2 sensor is probably the most important sensor in determining the amount of fuel being injected. without getting into a lesson plan on exactly how the Pcm determines injector pulse times, the O2 sensors, Coolant temp, air temp, throttle position, and air flow (maf) all combined with an algorithm are how it's done.

jesse

 

[jimithing]

I'm not getting any CEL, just suspect that the O2 sensors may be the reason why my truck is chugging gas.

The front O2 (upstream) sensors are aka the air/fuel sensor right?

I'm not really experiencing bad mileage in my V6 but I'm curious if this helps mileage at all. Do you have a place where you've kept good records of your mileage? Be nice to see some graphs before and after the change to see what effect changing the sensors has.

BTW, I use this site if you don't already have one.

http://www.fuelly.com

 

[Sungod]

What you read is wrong, or you misread. The upstream O2 sensor is probably the most important sensor in determining the amount of fuel being injected. without getting into a lesson plan on exactly how the Pcm determines injector pulse times, the O2 sensors, Coolant temp, air temp, throttle position, and air flow (maf) all combined with an algorithm are how it's done.

jesse

The topic is the 'downstream' sensor meaning past the catalytic converter. These are passive sensors. The sensor before the converter functions in the manner of what you described.

 

[Belovian]

The topic is the 'downstream' sensor meaning past the catalytic converter. These are passive sensors. The sensor before the converter functions in the manner of what you described.

I mentioned it because In your first post, you make no mention of upstream or downstream. You say "sensor" and them go on to say you"ll see no improvement if you replace "them". Also If you read my earlier Post in this thread I explain the differences between upstream and downstream.

Lastly, suggesting to someone to not replace a defective part especially one you don't seem real familiar as to the function is a bit weak.

jesse

 

[ronsta]

I'm not really experiencing bad mileage in my V6 but I'm curious if this helps mileage at all. Do you have a place where you've kept good records of your mileage? Be nice to see some graphs before and after the change to see what effect changing the sensors has.
BTW, I use this site if you don't already have one.
http://www.fuelly.com

You say you’re not really experiencing bad mileage, I’m sure mine has gone downhill gradually but it only hit me a little over a year ago that, “ damn I used to get over 400 miles to the tank & now I barely get 300!”. So that’s what really prompted me to find the cure. A lot of ppl I speak to face to face have the same issues. I have no qualms about knocking on someone’s window, introducing myself and talking to them. So far everyone I’ve spoken with face to face would want it fixed –within reasonable cost of course.
2 mechanics I spoke with adamantly say if O2 sensors go bad they go bad, nothing in between and it’ll definitely trip a CEL. Doing a google search yields a few promising results which support my theory & goes against what the mechanics said:
http://www.ehow.com/video_4754022_change-o2-sensor.html
http://www.autohausaz.com/html/emissions-oxygen_sensors.html
http://autoparts.lifetips.com/cat/61714/oxygen-sensors/index.html
btw I use Fuel Log app for android, been using it for the past 5 fillups
Can someone answer my question?
Is the air fuel sensor a separate animal than the 4 (2up/2down) O2 sensors?

 

[Sungod]

I mentioned it because In your first post, you make no mention of upstream or downstream. You say "sensor" and them go on to say you"ll see no improvement if you replace "them". Also If you read my earlier Post in this thread I explain the differences between upstream and downstream.

Lastly, suggesting to someone to not replace a defective part especially one you don't seem real familiar as to the function is a bit weak.

jesse

Who said anything about not replacing a defective part? The OP said that he was going to replace parts that had not failed. There is no point in replacing working parts. How is his mileage going to improve by replacing a downstream sensor that is passive and then replacing upstream that haven't failed? That is a bit weak.