Routine O2 oxygen sensor replacement?

[tomjonesBT33]

I was reading through the service manual last night and saw that BMW recommends that the O2 sensors be replaced every 100K miles in order to maintain emissions performance and improved gas mileage.

My car is at 219K and they have never been replaced. No codes. Just passed emissions and safety in January. I also tend to average about 23mpg commuter mileage (mix of highway speed and stop and go). Pure highway mileage is 31-32 mpg.

Just wondering if you folks with higher mileage cars change the sensors as a matter of routine per the BMW recommendation.

Thoughts or experiences?

[pokeybritches]

Originally Posted by tomjones20194

I was reading through the service manual last night and saw that BMW recommends that the O2 sensors be replaced every 100K miles in order to maintain emissions performance and improved gas mileage.

My car is at 219K and they have never been replaced. No codes. Just passed emissions and safety in January. I also tend to average about 23mpg commuter mileage (mix of highway speed and stop and go). Pure highway mileage is 31-32 mpg.

Just wondering if you folks with higher mileage cars change the sensors as a matter of routine per the BMW recommendation.

Thoughts or experiences?

I used to be a believer in casualty maintenance for the O2 sensors, but in the past few years I've started to lean towards preventative maintenance. Whether you need them depends on the number of cold starts and time spent at high load with rich mixtures that foul O2 sensors over time. The ECU runs routine diagnostics where it periodically measures O2 sensor response time and signal amplitude, all as part of OBD. At your mileage, I would replace the primary O2 sensors and leave the secondaries alone unless you start getting codes.

[tomjonesBT33]

Thanks pokey. I’ll add this to my maintenance list.

[3002 tii]

What pokey said, my car was running like shit for a little while before the actual CEL appeared for o2’s. Even the rear o2’s affect fuel trim levels slightly I believe, which is why so many folks who run catless without tunes sometimes report rough idling.

[pokeybritches]

Originally Posted by 3002 tii

What pokey said, my car was running like shit for a little while before the actual CEL appeared for o2's. Even the rear o2's affect fuel trim levels slightly I believe, which is why so many folks who run catless without tunes sometimes report rough idling.

Some cars do use "rear O2 control", where rear O2 sensor readings are incorporated into fuel trims. Post-cat narrowband readings tend to be more stable than pre-cat narrowband readings. Rear O2 control is less common on cars with wideband sensors.

I haven't confirmed whether some of the older models with narrowband sensors use rear O2 control, but I wouldn't be surprised. It's certainly possible to delete it with a tune. The MS45 and MSS70 ECUs both have options to enable "self learning" with 4 O2 sensors (2 per bank), or reduce all the way down to a single O2 sensor for 6-1 setups (not sure if this works since no one has tried it to my knowledge). To figure out what "self learning" means would require digging into the ECU further than I have gone *ahem* terra *ahem*