Replacing an downstream oxygen sensor

Xcellor

My BMW 520D is throwing an error which points to the post catalyst o2 sensor having a problem. Ive noticed when the engine is warm there is an intermittent rev even when the car is in park. Nothing drastic but not as smooth as it should be. Slight twitching. There is no engine light on.

Anyone have experience changing a sensor. I'm assuming its under the belly of the car. Any tips?

biko

Have a look on youtube for videos of how to diagnose it and then change it (or just clean it)
https://www.youtube.com/results?search_query=oxygen+sensor+symptoms

Steamed Clams

I presume you've an F10 520d, I don't believe the E60 has a downstream lambda even with the N47.



No. 16 in the diagram above, screwed in just below the cat/DPF. I think it's visible without removing the engine or transmission cover underneath, but I don't know if there's enough access to swing a spanner or get to the connector with the covers in place.

It's unlikely to cause any engine running problems though, no. 12 is the primary lambda sensor that's used in the feedback loop. The downstream lambda is generally only present to monitor the cat efficiency, and to throw the EML if there isn't a significant increase in O2 post cat. The error probably relates to the heater element in the sensor, or an open circuit, rather than the function of it? I'd expect you'd have an EML otherwise.

Since you don't have an EML on, I'd suggest looking at the condition of the swirl flaps and intake manifold for coking. Partially coked and clogged swirl flaps don't throw an EML, but can cause very similar idle problems. I had very similar idle issues on my 530d, idle dropping intermittently by ~100 RPM and quickly back up was causing a twitch at idle. I threw the very carbon-y and seized swirl flaps in the bin, flushed the manifold and problem solved

Xcellor

It is indeed an F10.

I've reviewed the following video
https://www.youtube.com/watch?v=O-UNkev5HWM

ANd I had live data obdc plugged in yesterday and the sensor in question was not moving despite revving the engine. The other sensor did read different values so something must be up with it?

Should I locate remove / clean first and check again before purchasing replacement. Looks like ~ 100 euro mark. Car is over 100,000 miles so suspect it has reached end of its life...

Xcellor

Steamed Clams wrote: »

I presume you've an F10 520d, I don't believe the E60 has a downstream lambda even with the N47.



No. 16 in the diagram above, screwed in just below the cat/DPF. I think it's visible without removing the engine or transmission cover underneath, but I don't know if there's enough access to swing a spanner or get to the connector with the covers in place.

It's unlikely to cause any engine running problems though, no. 12 is the primary lambda sensor that's used in the feedback loop. The downstream lambda is generally only present to monitor the cat efficiency, and to throw the EML if there isn't a significant increase in O2 post cat. The error probably relates to the heater element in the sensor, or an open circuit, rather than the function of it? I'd expect you'd have an EML otherwise.

Since you don't have an EML on, I'd suggest looking at the condition of the swirl flaps and intake manifold for coking. Partially coked and clogged swirl flaps don't throw an EML, but can cause very similar idle problems. I had very similar idle issues on my 530d, idle dropping intermittently by ~100 RPM and quickly back up was causing a twitch at idle. I threw the very carbon-y and seized swirl flaps in the bin, flushed the manifold and problem solved

Yes I wouldn't have expected it to be the downstream causing an issue but it is very subtle. Literally I can be driving around fine then stop and I'll feel a slight rev maybe 25 + rpms. But more often than not I dont perceive anything.

You mention

"swirl flaps and intake manifold for coking" WHat and where are these? Any spray type things that can be used or am I best just replacing?

Since the sensor is not showing signs of life I reckon I should start there first process of elimination and all and it appears to be DIYable...

One thing. Tools for removing? SPecial spanner needed right??

Xcellor

Just to give an update.

I replaced #16 the post cat o2 lambda sensor to get access I needed to remove the cover underneath the car, good few screws but fairly easy.

I didn't have a huge amount of space but the part is quite exposed so was able to get a spanner in and loosen and replace. Very straightforward.

Fired up the car again and checked the voltage of the sensor and it was showing voltage and was changing if i put accelerator down. So the obvious fault was fixed.

Using Torque pro the fault was still showing though and despite clearing (weith Torque pro) wasn't going away. So I downloaded ISTA+ (Needs ENET cable) which is the dealer software and ran a scan. The tool is VERY good gives much more information and provides info on what to do when the fault occurs.

So it said to check cables etc and then replace the sensor and after replacing sensor delete customization on one of the ECUs apparently over time the car learns stuff and this needs to be reset if the part is replaced. I did this and then used the the same tool to clear the fault and sure enough now it's gone.

One thing that ISTA+ is warning is that the DPF is approaching it's limit. I believe this is just a predetermined fault which will come based on the mileage alone. I've no interest in replacing DPF is there any maintenance I can do like addictive to fuel? The car is driven 1 hour each day at 80-100kph so getting up to good temperatures.