When to Replace O2 Sensors on 4.5L Turbo Model?

[spooltime]

I did a search and couldn't find anything of much use.

 

What's the consensus on when O2 sensors on the turbo engine should be replaced?  Is there a specific mileage requirement, or is it sufficient to rely on the ME 7.1.1's built-in O2 sensor monitoring function and just wait until the "check engine" light illuminates with a corresponding O2 fault code?  The O2 sensors do not appear on either the "minor" or "major" service checklists.  I note that replacement Bosch sensors are supposed to have a service life of approximately 167,500 miles before requiring replacement, but I've always had it in my mind that to maintain optimal performance and fuel efficiency, these ought to be done at about 100,000.  Anyway, my Cayenne has tipped to the north side of 100,000 miles, so hence the questions.  TIA.

 

 

[JFP in PA]

I did a search and couldn't find anything of much use.

 

What's the consensus on when O2 sensors on the turbo engine should be replaced?  Is there a specific mileage requirement, or is it sufficient to rely on the ME 7.1.1's built-in O2 sensor monitoring function and just wait until the "check engine" light illuminates with a corresponding O2 fault code?  The O2 sensors do not appear on either the "minor" or "major" service checklists.  I note that replacement Bosch sensors are supposed to have a service life of approximately 167,500 miles before requiring replacement, but I've always had it in my mind that to maintain optimal performance and fuel efficiency, these ought to be done at about 100,000.  Anyway, my Cayenne has tipped to the north side of 100,000 miles, so hence the questions.  TIA.

 

When the vehicle codes, indicating that the sensor is failing,

[spooltime]

When the vehicle codes, indicating that the sensor is failing,

 

 

So no reason to do preventative maintenance before one of the sensor codes?  I've always understood that as the "pre" sensor wears out, the mixture starts richening up and fuel efficiency declines..  Just trying to stay ahead of the curve.

[ARModen]

There's two per side in series.  Most likely you'll see cat efficiency codes pop up well before you have any significant change in fuel efficiency.

[JFP in PA]

 

When the vehicle codes, indicating that the sensor is failing,

 

 

So no reason to do preventative maintenance before one of the sensor codes?  I've always understood that as the "pre" sensor wears out, the mixture starts richening up and fuel efficiency declines..  Just trying to stay ahead of the curve.

 

 

We have seen some O2 sensors fail in 25K miles, and others still be running fine at 250K miles, so I have no idea what a "preemptive" sweet spot should be.  And long before you would see a measurable mileage change, the car will code; the system is designed to behave that way.  Besides which, O2 sensors are anything but cheap.

[spooltime]

Thanks for the replies.  I'll defer doing this job for the time being.

[RFM]

http://rb-aa.bosch.com/boaa-uk/Product.jsp?prod_id=35&ccat_id=21&language=en-GB&publication=1 This is a recommendation from Bosch.