Help - MOT failure on CO - oxygen sensor? Which one?

[MiniNinjaRob]

Originally Posted by omc 47

Hi NinjaRob,
Yes that is the Lambda sensor in your pickys, I have 2 940's and they are both on the down pipe from the turbo.
I've had issues with the CO readings before now and found the 3 bolts (holding the turbo on the down pipe) needed clamping up a little tighter.
This connection is a dry perfect fit and if not completely sealed fools the ECU into making the mixture richer because the Lambda sensor is sensing too much oxygen in the first part of the pipe after the turbo................

Thanks I'll give that a try. Pity I can't test the CO myself until I get to the MOT test again.

[MiniNinjaRob]

Thanks all for the help. Managed to get the sensor out quite easily with a locking adjustable.

I reckon this might be the original one.



Was very white on the end, cable didn't look very good at all and it looks generally pretty knackered.





Time for a new one I think. At least I am 100% on the one I need now.

One last thing. I have read that the EGR valve might need cleaning out too but I'm not 100% I have one as mine is too new a 940. I assume this bit that is blanked off on the inlet manifold is where the EGR attach to so that means I don't have one. Am I right?

[RollingThunder]

I also bought an NTK Lambda Sensor OZA446-E58, and finally fitted it yesterday! This is the correct part for my 1998 LPT, and I reckon it'll be the right one for your car too. Like yours, my old one looks like it was the original Bosch part and was looking well past its best.

Once the car was up on ramps it took literally under 10 mins to change including getting the part out of the box

BTW Mine also 'hangs' underneath the downpipe, so yours doesn't look original - and there is only the one O2 sensor on our cars. I suspect someone has either replaced your downpipe, or else added a second sensor for an air-fuel ratio gauge?

HTH

[MiniNinjaRob]

My car has a Tony Banks Stainless system on it. I think it must be a full system as the sensor came out really easy and there is no rust at all on the down pipe. The sensor cable seemed ridiculously long so maybe the new location they put it in was located nearer the turbo than standard?

[MiniNinjaRob]

Car doesn't have a AFR gauge and the previous owners didn't do any modifying and weren't the sort of people to do mods anyway.

[Forrest]

The position RollingThunder describes very well is where I was describing very badly that you look. It sounds as though your after-market exhaust has the sensor port in a different place, but it would be worth checking underneath the pipe nearer the turbo to see if there is a blanked off port since the Volvo front pipes usually have two, but on later cars only use the front-most one. It is possible your "front" sensor was reinstalled in the rear port when the exhaust was changed.

That is the Bosch OEM original part number. If the lead length is as issue LSH-06 is an identical sensor with a shorter lead. Personally, I like to have plenty of lead to enable routing well away from hot exhaust parts.

[TonyS9]

You can't tell from the look of it really, its a pretty harsh environment, yours looks fine. The symptom can be caused by exhaust leaks or a faulty sensor.

For EGR you don't have one, but it's not like diesel they don't seem to need attention. It is attached to the left side of the exhaust manifold and the top of the inlet manifold.

[MiniNinjaRob]

I've ordered a NTK sensor as you guys have recommended.

Just like to say thanks for all the help, hopefully this will sort this emissions issue and I will have learnt something new - again! It's a lovely car and had a lot of money spent on it so I think the engine is a good-un - certainly didn't complain one bit as I drove it at 4500rpm for 20 minutes to try and clear the crap out on the way to the MOT.

[Rversteeg]

As far as I know there is only one O2 sensor active and it will ALWAYS be placed upstream of the catalytic converter. This sensor is used by the ECU to determine whether the engine is running too rich or too lean by looking at the exhaust gas content.
If the engine is running rich, the cat will "afterburn" the unburned fuel in the exhaust gas. So if the O2 sensor would have been placed after the cat, it would measure an already treated exhaust gas, so the content information would be useless for the ECU.
On modern cars you see sensor before and after the cat, with the one after the cat for checking the functionality of the cat.

[MiniNinjaRob]

UPDATE.
I had a look round the turbo and the downpipe and could feel a blanked or welded up hole underneath the downpipe a few cm from the turbo - probably the one you guys were talking about. I can't find any others.

The car had the turbo renewed and a whole new exhaust fabricated so I reckon it was repositioned. Good for me as I can replace the sensor from above - result!

I really hope this works as I'm stumped otherwise. Sensor comes on Wednesday.