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Discussion Starter #1
How bad will the bad o2 censer effect My fuel economy in My 05 avalanch 5.3?
I have the part I am just not up to changing it and I have a 12 hour drive on fri.
 

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Yes on the passenger side after the cat.
What Lundbergh said is also true. Downstream O2 doesnt affect mileage/performance.It is only to detect cat converter operation and to set a code when the cat is not performing to a certain specification.It has no affect on performance

A lazy or dead heater circuit on an upstream cat causes the O2 to heat by itself , from exhaust temp. That takes longer, hence the longer period before closed loop operation.

I wasnt sure which O2 you were referring to.pre cat- post cat. etc
 

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Discussion Starter #6
I have a rain day today and a box of o2 censers I have pulled out of GM trucks . I might get off My lazy ass and swap it out for shits and giggles. I should check the beer supply in the shop anyways .
 

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If you have the code return after replacement, check the O2 heater fuses under the hood. Another common issue that will set that code is the harness rubbing on the front driveshaft, cutting through wiring.
 

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GM tech here, ANY problem with Any of the O2 sensors will cause the engine to run is a fixed rate fuel curve that will severely hurt fuel mileage. FYI.

All these responses are wrong.

It is the O2 sensor heater circuit. It wont affect mileage much, if at all. It will warm up slower which may delay closed loop operation a few more minutes.
After the cat won’t affect mileage, it’s basically only there to monitor catalyst efficiency.
What Lundbergh said is also true. Downstream O2 doesnt affect mileage/performance.It is only to detect cat converter operation and to set a code when the cat is not performing to a certain specification.It has no affect on performance

A lazy or dead heater circuit on an upstream cat causes the O2 to heat by itself , from exhaust temp. That takes longer, hence the longer period before closed loop operation.

I wasnt sure which O2 you were referring to.pre cat- post cat. etc
 

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Heck, if you have the part just throw it in. Two tricks I've learned over the years - don't try to crack it loose stone cold. You will rip the threads right off. Get it nice and hot on a decent drive and get under there and crack it loose while the exhaust pipe is still hot. But first... on the day before, soak some penetrating lube into it.

If you're not up to it yet, don't sweat it - drive on. Like mentioned, the pre cat 02s control your fuel trims, the post #2s just monitor cat health. I've never had an issue or noticed any difference driving with a bad post cat 02.

The key to the check engine light is - don't drive if it's flashing. Flashing means things so out of whack damage can occur. Just on steady, means fix it when you get around to it.
 

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GM tech here, ANY problem with Any of the O2 sensors will cause the engine to run is a fixed rate fuel curve that will severely hurt fuel mileage. FYI.

All these responses are wrong.
Do you have any proof that “all these responses are wrong”?
I’m currently an FCA tech but also spent a good part of my career in a private shop. Downstream (post cat) 02 sensors are primarily to monitor catalytic converters efficiency, and will not noticeably affect fuel mileage. The ECM will not calibrate fuel based on post cat readings as those readings will be directly affected by how good the cat is working, that’s why there are pre-cat sensors.
if you don’t believe me you can watch your fuel trim numbers as you disconnect a rear sensor, the numbers still read and change based on the standard parameters.
If you have any better info about this feel free to post it up-I love to learn new things.
 

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GM tech here, ANY problem with Any of the O2 sensors will cause the engine to run is a fixed rate fuel curve that will severely hurt fuel mileage. FYI.

All these responses are wrong.
is the function of the o2 sensors to moniter a/f and adjust all sorts of things, like cam timing and fuel?
do they get all carboned up and not read correctly and foul the tune because of this? just curious how important they are.
 

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Heck, if you have the part just throw it in. Two tricks I've learned over the years - don't try to crack it loose stone cold. You will rip the threads right off. Get it nice and hot on a decent drive and get under there and crack it loose while the exhaust pipe is still hot. But first... on the day before, soak some penetrating lube into it.

If you're not up to it yet, don't sweat it - drive on. Like mentioned, the pre cat 02s control your fuel trims, the post #2s just monitor cat health. I've never had an issue or noticed any difference driving with a bad post cat 02.

The key to the check engine light is - don't drive if it's flashing. Flashing means things so out of whack damage can occur. Just on steady, means fix it when you get around to it.
You can just crack it. Then lube with brake fluid. Worked for years at Toyota and saved many manifold replacements.
 

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You
GM tech here, ANY problem with Any of the O2 sensors will cause the engine to run is a fixed rate fuel curve that will severely hurt fuel mileage. FYI.

All these responses are wrong.
just keep thinking that sonny. Good for you.
 

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is the function of the o2 sensors to moniter a/f and adjust all sorts of things, like cam timing and fuel?
do they get all carboned up and not read correctly and foul the tune because of this? just curious how important they are.
Yes on the A/F ratio. O2 sensor readings adjust the mix.

Also A/F ratio is used by the algorithms of the software, as well as many other sensor readings, in unison to calculate all kinds of settings/parameters to run the engine.

The A/F ratio of the upstream sensor is used to "Trim " or more precisely" tailor" fuel delivery for optimum mileage. An O2 heater that is non functioning can affect fuel mileage some , more so with a cold engine and short trips. On a longer trip or long trips , the engine exhaust heat is sufficient in 98 percent of most cases to keep the sensor reading properly.
They use Heaters to warm the sensor up sooner to obtain closed loop operation earlier during engine operation to help clean up cold start emissions.
 

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Discussion Starter #15
Just to say ! I swapped out all 4 today with ones I had that looked like new. I cleared all codes and moved on to fixing stone chips on the hood and then did a thorough clean on the interior. All the o2 s came out easy no heat needed.
By the time I was done I had done a very good cleaning on the beer fridge so the test drive will have to be tomorrow .
 

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After the cat won’t affect mileage, it’s basically only there to monitor catalyst efficiency.
if op has hptuners he could just turn
Just to say ! I swapped out all 4 today with ones I had that looked like new. I cleared all codes and moved on to fixing stone chips on the hood and then did a thorough clean on the interior. All the o2 s came out easy no heat needed.
By the time I was done I had done a very good cleaning on the beer fridge so the test drive will have to be tomorrow .

right on. I got a Silverado about the same year, I went through and turned off a bunch of that stuff to save the headache. Catalyst, evap,etc. if you keep having trouble lemme know I could send you my tune file if you have Hptuners.
 

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Discussion Starter #18
if op has hptuners he could just turn



right on. I got a Silverado about the same year, I went through and turned off a bunch of that stuff to save the headache. Catalyst, evap,etc. if you keep having trouble lemme know I could send you my tune file if you have Hptuners.
Thanks for the offer! I need to get a new cable to link up with My lap top. I was welding up a trailer last winter and could smell plastic burning and by the time I saw it burning it was to late. took out the cable and fried the lap top .
 

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Discussion Starter #19
If you have the code return after replacement, check the O2 heater fuses under the hood. Another common issue that will set that code is the harness rubbing on the front driveshaft, cutting through wiring.
Nice tip! When I was under the hood today I pulled and cleaned all the connections. All are good to go.
 
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