Help -Oxygen sensor warning light (E85, 2.5 SE)

[Mike6]

Help.
Only last week did I resolve other warning lights (front wheel sensors) than an old friend has come back to haunt me just before MOT time.
Yes its the yellow engine light which using my new and brilliant scanner is telling me the heater element in bank 2 downstream (post cat)oxygen sensor is failing.
Not good a climbing under cars these day (blood pressure issues) I asked my trusted MOT station if they could replace it and they said yes with parts they get from Styners. So I google the cost of genuine BMW sensors and they seem staggeringly expensive around £270 each.
Going to do it myself but would be grateful for advice following searches on this site which suggest all manner of actions needed to access these lower sensors.
Do I:
remove undertray
Jack up car and remove road wheel
remove supporting bracket for exhaust
Access sensor using special tool or spanner
or is it more complicated?

Also oxygen sensors seem widely available ranging from about £20 on ebay up to aound £100 for Bosch or a bit less using DENSO. Which ones are recommended.
Thanks for any advice

[BumpyZ4]

Nope it's that easy. If you are limber you can forego removing the under tray and still get to both downstream sensors. I always use Bosch, reasonably priced and are usually bullet proof.

[bigwinn]

Pre cats are fairly easy to get at with the removal tool- not a biggie

The lower ones are not great unless you remove the heat shield

Where you based?

[patriot66]

Hi Mike. I took this reference photo earlier this year with my car up on axle stands whilst installing my supercharger. My Z4 is a '03 M54 2.5i You can just make out one of the lambda sensors.

Exhaust.jpg (161.14 KiB) Viewed 640 times

You will need to drop the exhaust from the front two flanges backwards and the studs and bolts on these are notorious for corroding very badly so that they need cutting/grinding/drilling to remove them I had them removed with a plasma cutter. Once you get to the stage shown in the photo then access is VERY tight but probably manageable

[Mike6]

I am still confused . Some earlier posts suggested you needed to take apart this notorious exhaust joint whilst others said you only need to remove the exhaust support bracket which does seem logical.
Similar with these helpful posts but no way am I going to start breaking exhaust joints with car just jacked up.
Is there a definitive answer.
I live in East grinstead, West Sussex

[bigwinn]

I am still confused . Some earlier posts suggested you needed to take apart this notorious exhaust joint whilst others said you only need to remove the exhaust support bracket which does seem logical.
Similar with these helpful posts but no way am I going to start breaking exhaust joints with car just jacked up.
Is there a definitive answer.
I live in East grinstead, West Sussex

Mike

I’ll defer to others

However when I took the last part off the car I was scrapping last night which was the heat shield, John and I could both see straight down into the space where we could have easily attached the tool and popped them out

The caveat is that to remove the heat shield you have several awkward bolts on that and you’d have to disconnect the steering shaft

I guess either way you have pain to do it, exhaust route or shield route…

[BumpyZ4]

I am still confused . Some earlier posts suggested you needed to take apart this notorious exhaust joint whilst others said you only need to remove the exhaust support bracket which does seem logical.
Similar with these helpful posts but no way am I going to start breaking exhaust joints with car just jacked up.
Is there a definitive answer.
I live in East grinstead, West Sussex

I've got a M54 3.0 and i just changed both downstream O2 sensors without removing the under tray or exhaust. Just jacked it up, removed the wheel because it was in the way of my belly and replaced the sensors. One is very easy to change with a spanner but the other one you have to be a little more creative with a O2 sensor socket and extensions. The hardest part for me was routing the sensor cables!

[patriot66]

I am still confused . Some earlier posts suggested you needed to take apart this notorious exhaust joint whilst others said you only need to remove the exhaust support bracket which does seem logical.
Similar with these helpful posts but no way am I going to start breaking exhaust joints with car just jacked up.
Is there a definitive answer.
I live in East grinstead, West Sussex

Unfortunately the exhaust support bracket is secured by the same corroded studs and bolts on the exhaust flanges. Slightly fuzzy photo but this was the state mine were in Also doubt just removing that bracket will get you any more access to the lambdas.

20200623_154323.jpg (139.28 KiB) Viewed 591 times

Intrigued by what Stu BigWinn said about access from above I went out to my car just now and took a few photos looking down the back corner of the engine and with some illumination you can see both lambdas...just.

20220720_184459.jpg (167.82 KiB) Viewed 591 times

20220720_184400.jpg (93.27 KiB) Viewed 591 times

20220720_184705.jpg (73.46 KiB) Viewed 591 times

Having now had a good look I agree with Stu that they could be changed from above BUT the heat shield and steering shaft would have to be removed

[patriot66]

I am still confused . Some earlier posts suggested you needed to take apart this notorious exhaust joint whilst others said you only need to remove the exhaust support bracket which does seem logical.
Similar with these helpful posts but no way am I going to start breaking exhaust joints with car just jacked up.
Is there a definitive answer.
I live in East grinstead, West Sussex

I've got a M54 3.0 and i just changed both downstream O2 sensors without removing the under tray or exhaust. Just jacked it up, removed the wheel because it was in the way of my belly and replaced the sensors. One is very easy to change with a spanner but the other one you have to be a little more creative with a O2 sensor socket and extensions. The hardest part for me was routing the sensor cables!

Fair play to you sir ! You must be VERY flexible !

[bigwinn]

I am still confused . Some earlier posts suggested you needed to take apart this notorious exhaust joint whilst others said you only need to remove the exhaust support bracket which does seem logical.
Similar with these helpful posts but no way am I going to start breaking exhaust joints with car just jacked up.
Is there a definitive answer.
I live in East grinstead, West Sussex

I've got a M54 3.0 and i just changed both downstream O2 sensors without removing the under tray or exhaust. Just jacked it up, removed the wheel because it was in the way of my belly and replaced the sensors. One is very easy to change with a spanner but the other one you have to be a little more creative with a O2 sensor socket and extensions. The hardest part for me was routing the sensor cables!

Fair play to you sir ! You must be VERY flexible !

Or double jointed!

Skills!

[Mike6]

Thank you for advice. Think the way forward when childminding duties permit is to jack car up and get under there for a dummy or exploratory run before buying the sensor. Come to think of it the twin grandkids are 3 years old so could send them under to do the job.

[Mike6]

Managed to get time to jack car up on one side and using a light and mirror I can easily see one sensor right where the exhaust join is and sandwiched between the two pipes. Is this sensor2 on bank1. Mine is sensor 2 on bank 2 and from the looks of the pics on previous post this looks like it is slightly higher up the header towards the cat.
Can anyone confirm this for me please as the last thing i want to do is rupture myself replacing the wrong one.
Thanks