Pre-Cat O2 sensors

bmwhitman · 05-18-2016, 04:47 PM

What are peoples thoughts about changing O2 sensors preventatively at 150,000 km (100,000 miles)? Any benefits?

KNS · 05-19-2016, 01:26 PM

At around 100,000 miles the sensors start to get "lazy" even though they're still working.

I changed the pre cat O2 sensors on my E46 at around 90,000 miles even though I had no indication they were failing. At 205,000 miles I got a SES light (service engine soon with lean codes). I replaced the pre cat O2 sensors and the light has stayed off.

So, just based on my experience with my E46, 100K has been a good benchmark and I always replace the O2 sensor on any car I own when it hits 100K miles.

bmwhitman · 05-19-2016, 05:34 PM

Quote:

Originally Posted by KNS

At around 100,000 miles the sensors start to get "lazy" even though they're still working.

I changed the pre cat O2 sensors on my E46 at around 90,000 miles even though I had no indication they were failing. At 205,000 miles I got a SES light (service engine soon with lean codes). I replaced the pre cat O2 sensors and the light has stayed off.

So, just based on my experience with my E46, 100K has been a good benchmark and I always replace the O2 sensor on any car I own when it hits 100K miles.

Good to know I'll put on my summer to do. Is this an easy DIY?

KNS · 05-19-2016, 05:51 PM

I haven't done the pre cat sensors on my 128i (similar to your 330) but they look accessible so hopefully not too hard.

Efthreeoh · 05-21-2016, 08:35 AM

On my '06 325i E90 I lost the Bank 2, Sensor 1 at 126,000 miles. The other three original sensors have remained in the car, which is now at 302,000. I've not noticed any drivability issues and I keep strict fuel mileage records. I have seen a small drop in average MPG of less than 0.5 MPG from the car's early life until now. I use the car as a DD (obviously) and my commute is almost "laboratory" consistent. I'll take the drop in MPG as due to age.

Other experience I've had with O2 sensors is my 1999 F-150 (sold it a year ago). Around 100,000 miles I lost the Bank 2 Sensor 1 on the F150. Being the sensors are not that expensive for the F150, I bought both the upstream and down stream sensors for both banks of cylinders. The sensors were Bosch (OEM) aftermarket. I installed all 4 sensors and right after the Bank 1 catalytic converter came up defective. So I reinstalled the old sensors on the Bank 1 side and the bad catalytic code cleared and remained cleared. This is the reason I've left the O2 sensors alone in the E90.

My 2 cents.

Efthreeoh · 05-21-2016, 08:48 AM

Quote:

Originally Posted by bmwhitman

Good to know I'll put on my summer to do. Is this an easy DIY?

O2 sensors can really be a pain in the ass. But if you use a good amount of penetrating oil, take time, and have the right tools, they can come out pretty easily.

mlifxs · 05-22-2016, 05:21 PM

thanks for the views here.

i've got 155k miles on my orig sensors. my mpg might be lower, but I could be driving it harder.

over the last year, I started getting fuel mixture errors, and a couple misfires, even after changing all coils and plugs. resetting adaptations appears to cure the misfires and mixture errors, usually for a month or two.

so, I'm interested in exploring the o2 sensor angle and hope to do some data logging on sensor voltage.

any thoughts or suggestions are appreciated.

mweisdorfer · 05-22-2016, 06:54 PM

There is a video on YouTube regarding how to change the down pipes on a 335i. Anyways about 7-8 min in, he shows you how to take out the O2 sensors on a 335i.

The pre-cat O2 sensors on a 335i will run about $225.00 for the set.

It's not worth changing the post-cat O2 sensors unless they go bad. It's my understanding that all they do is check to see that the pre-cat O2 sensors are working correctly.

05-18-2016, 04:47 PM	#1
bmwhitman Private First Class 46 Rep 177 Posts Drives: E90 Join Date: Aug 2011 Location: Toronto iTrader: (0) Garage List 2006 BMW 330i (E90) [0.00]	Pre-Cat O2 sensors What are peoples thoughts about changing O2 sensors preventatively at 150,000 km (100,000 miles)? Any benefits?
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05-19-2016, 01:26 PM	#2
KNS Lieutenant 137 Rep 439 Posts Drives: 128i and Porsche Join Date: Dec 2014 Location: Arizona iTrader: (0)	At around 100,000 miles the sensors start to get "lazy" even though they're still working. I changed the pre cat O2 sensors on my E46 at around 90,000 miles even though I had no indication they were failing. At 205,000 miles I got a SES light (service engine soon with lean codes). I replaced the pre cat O2 sensors and the light has stayed off. So, just based on my experience with my E46, 100K has been a good benchmark and I always replace the O2 sensor on any car I own when it hits 100K miles.
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05-19-2016, 05:51 PM	#4
KNS Lieutenant 137 Rep 439 Posts Drives: 128i and Porsche Join Date: Dec 2014 Location: Arizona iTrader: (0)	I haven't done the pre cat sensors on my 128i (similar to your 330) but they look accessible so hopefully not too hard.
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05-21-2016, 08:35 AM	#5
Efthreeoh General 17303 Rep 18,727 Posts Drives: The E90 + Z4 Coupe & Z3 R'ster Join Date: May 2012 Location: Virginia iTrader: (0)	On my '06 325i E90 I lost the Bank 2, Sensor 1 at 126,000 miles. The other three original sensors have remained in the car, which is now at 302,000. I've not noticed any drivability issues and I keep strict fuel mileage records. I have seen a small drop in average MPG of less than 0.5 MPG from the car's early life until now. I use the car as a DD (obviously) and my commute is almost "laboratory" consistent. I'll take the drop in MPG as due to age. Other experience I've had with O2 sensors is my 1999 F-150 (sold it a year ago). Around 100,000 miles I lost the Bank 2 Sensor 1 on the F150. Being the sensors are not that expensive for the F150, I bought both the upstream and down stream sensors for both banks of cylinders. The sensors were Bosch (OEM) aftermarket. I installed all 4 sensors and right after the Bank 1 catalytic converter came up defective. So I reinstalled the old sensors on the Bank 1 side and the bad catalytic code cleared and remained cleared. This is the reason I've left the O2 sensors alone in the E90. My 2 cents. __________________ A manual transmission can be set to "comfort", "sport", and "track" modes simply by the technique and speed at which you shift it; it doesn't need "modes", modes are for manumatics that try to behave like a real 3-pedal manual transmission. If you can money-shift it, it's a manual transmission. "Yeah, but NO ONE puts an automatic trans shift knob on a manual transmission."
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05-22-2016, 05:21 PM	#7
mlifxs Diamond Geezer 212 Rep 2,385 Posts Drives: Jet Black 2007 328i Saloon Join Date: Nov 2007 Location: Florida iTrader: (6) Garage List 2016 VW Golf Sportw ... [10.00]	thanks for the views here. i've got 155k miles on my orig sensors. my mpg might be lower, but I could be driving it harder. over the last year, I started getting fuel mixture errors, and a couple misfires, even after changing all coils and plugs. resetting adaptations appears to cure the misfires and mixture errors, usually for a month or two. so, I'm interested in exploring the o2 sensor angle and hope to do some data logging on sensor voltage. any thoughts or suggestions are appreciated.
	Appreciate 0 Quote

05-22-2016, 06:54 PM	#8
mweisdorfer Major General 1903 Rep 6,968 Posts Drives: 2007 Black/Black 335i e90 Join Date: Apr 2011 Location: Holly, MI iTrader: (0) Garage List 2007 BMW E90 335i [0.00] 2008 bmw x5 [0.00]	There is a video on YouTube regarding how to change the down pipes on a 335i. Anyways about 7-8 min in, he shows you how to take out the O2 sensors on a 335i. The pre-cat O2 sensors on a 335i will run about $225.00 for the set. It's not worth changing the post-cat O2 sensors unless they go bad. It's my understanding that all they do is check to see that the pre-cat O2 sensors are working correctly.
	Appreciate 0 Quote