Preventive o2 sensor replacement

[wander2039]

The back story on this.. replaced the o2 on Bank 2 upper last year due to code for the heater. On this trip a rodent a rodent in Laramie found whatever Chevy uses on the protective sleeve tasty and chewed through the wires on Bank 1 upper. All sorts of bad things happen when the signal wires short out. Made it to Wells Nevada and had to wait till the next day for a Denso but they ordered the wrong one. Spliced the wires and made it to Sacramento where Oreillys had it in stock.

Would you go ahead and replace the down streams? In my mind their only their to monitor and the cats and not as important. I could be wrong on the Chevy 6.0. My wife wants me to change.. and she's typically right lol. FYI I only use Denso's..

 

[slacktide_bitog]

The downstream is still worth replacing, especially if the job is easy on it

 

[spasm3]

I replace my upstream o2 sensors at the 75-90k mark. I've never replaced downstream, never had one go bad. But if its easy. Unless the newer software is different, the down streams just monitor the cat effectiveness. The upstream and downstream should not match, if the do, the trip the bad cat codes.

 

[Timmastertech]

Downstream sensors do far more than monitor the cat. The newer you get the more the downstreams do. The downstream sensors do have an affect on fuel control. How much depends on the manufacturer and the vehicle. I have had failed downstream sensors cause strange driveability issues. You have to remember that one of the primary functions of the engine management system is to keep tailpipe out emissions low. In order to do this, it needs to control feed gases into the converter. OEMs have moved towards controlling the feed in by looking at what comes out. This is a bit of a simplification. To cover everything my company teaches as far as air/fuel management and o2/Af sensors is 16 hours of instructor led class 2 with 2 prerequisite classes of 4 hrs each. 4 hours of that time is solely spent on oxygen and af sensors. This is a far more complex topic that most DIYers and even many professionals realize

 

[spasm3]

Downstream sensors do far more than monitor the cat. The newer you get the more the downstreams do. The downstream sensors do have an affect on fuel control. How much depends on the manufacturer and the vehicle. I have had failed downstream sensors cause strange driveability issues. You have to remember that one of the primary functions of the engine management system is to keep tailpipe out emissions low. In order to do this, it needs to control feed gases into the converter. OEMs have moved towards controlling the feed in by looking at what comes out. This is a bit of a simplification. To cover everything my company teaches as far as air/fuel management and o2/Af sensors is 16 hours of instructor led class 2 with 2 prerequisite classes of 4 hrs each. 4 hours of that time is solely spent on oxygen and af sensors. This is a far more complex topic that most DIYers and even many professionals realize

Thanks for the info! Looks like the downstreams are in fact more involved in the fuel management than in the '90s. Good to know!

 

[Timmastertech]

yes and no, The first downstream sensors actually appeared in the 80s from Toyota and Saab and were the primary fuel control or possibly the only fuel control feedback. The reason being is that after the gases go through the cat you get a more homogeneous mixture and a better picture of the operating conditions of the engine. The trend from the OEMs has been moving the upstream sensor closer and closer to the cylinder head for faster warmup. Lots of newer engine designs have the exhaust manifold integrated into the cylinder head with the cat close coupled to the head with the upstream sensor right at the flange. This is awesome for sensor and converter warmup but because of the close proximity of the sensor to the exhaust ports the sensor sees more of a cylinder by cylinder picture instead of an overall. We can use this to our advantage, however. Starting in 2011 model year the regulations required the OEMs to be able to detect a cylinder to cylinder A/f ratio imbalance. This is done by comparing upstream and downstream and knowing what cylinder was contributing exhaust at what time. All of this allows lower tailpipe out emissions, better fuel economy and longer converter life. Manufacturers starting implementing the AF imbalance monitor in the mid to late 2000s.

 

[wander2039]

I've watched a lot of Eric O and Pine Hollow so I know o2 sensors on some engines can be complex... just wasn't sure on the Chevy 6.0. The fuel trims look acceptable now, when it was messing up -25. The more I think about probably ought to change them due to the sleeve, they'll probably get eaten before they fail. Have 2k miles left on trip but have a 8k trip to Alaska next year. 81k on it right now.

 

[Wolf359]

yes and no, The first downstream sensors actually appeared in the 80s from Toyota and Saab and were the primary fuel control or possibly the only fuel control feedback. The reason being is that after the gases go through the cat you get a more homogeneous mixture and a better picture of the operating conditions of the engine. The trend from the OEMs has been moving the upstream sensor closer and closer to the cylinder head for faster warmup. Lots of newer engine designs have the exhaust manifold integrated into the cylinder head with the cat close coupled to the head with the upstream sensor right at the flange. This is awesome for sensor and converter warmup but because of the close proximity of the sensor to the exhaust ports the sensor sees more of a cylinder by cylinder picture instead of an overall. We can use this to our advantage, however. Starting in 2011 model year the regulations required the OEMs to be able to detect a cylinder to cylinder A/f ratio imbalance. This is done by comparing upstream and downstream and knowing what cylinder was contributing exhaust at what time. All of this allows lower tailpipe out emissions, better fuel economy and longer converter life. Manufacturers starting implementing the AF imbalance monitor in the mid to late 2000s.

But do they really wear out? I thought the advantage of changing out the upstream ones is that they get exposed to more of the raw exhaust and wear out or get lazy. The downstream ones don't switch that much and they're looking at a clean exhaust so don't really wear out. That's why I haven't had to change the downstream ones even with over 200k on a car.

 

[Timmastertech]

But do they really wear out? I thought the advantage of changing out the upstream ones is that they get exposed to more of the raw exhaust and wear out or get lazy. The downstream ones don't switch that much and they're looking at a clean exhaust so don't really wear out. That's why I haven't had to change the downstream ones even with over 200k on a car.

There isnt anything inside an oxygen sensor to wear. Its a chemical reaction that occurs inside the sensor that produces the output voltage you see. A simplification we use to help people think about is it to think of it as a miniature battery producing voltage based on a chemical reaction. Just like a battery eventually breaks down so too does any oxygen sensor.

 

[Wolf359]

There isnt anything inside an oxygen sensor to wear. Its a chemical reaction that occurs inside the sensor that produces the output voltage you see. A simplification we use to help people think about is it to think of it as a miniature battery producing voltage based on a chemical reaction. Just like a battery eventually breaks down so too does any oxygen sensor.

Then would you say that the upstream ones will wear out faster than the downstream or do they wear at the same interval? Basically I've had upstream ones throw a code when they wore out, but the downstream ones even at over 200k never threw a code.

 

[Timmastertech]

Then would you say that the upstream ones will wear out faster than the downstream or do they wear at the same interval? Basically I've had upstream ones throw a code when they wore out, but the downstream ones even at over 200k never threw a code.

not necessarily

 

[2EHA]

as stated by tim some older cars do infact use the upstreams as the monitor and downstreams for primary control