Yes, you will need a specialized λ-sensor spanner. £26 is not that bad, but if you are sufficiently friendly with a mechanic you can maybe borrow one?
Also, remove one bolt from the top engine stabiliser bar so you can tilt the engine forward to give you more space and get ot it from the top.
It is s pig of a job, but can be done in situ.

 

Not going to tilt the engine myself!

The specialist I go to would probably do it for me for a low price but buying the weird wrench would be cheaper. Just concerned it won't fit in there which would be a waste of money...

At least the heat shield and pre cats are gone so there's actually prospect of doing it!

 

Not going to tilt the engine myself!

not much to it, you just have to push it just a couple of cm to allow access. It is going nowhere by itself. I can't remeber if you have to undo the exhaust flexis too.

 

I use this set...

Pardon our interruption...

 

It should turn with a 22mm spanner, I've changed a few in the last couple of weeks and they all just cracked off and wound out. If its not turning with a good length 22mm spanner, I hope the threads haven't crossed or seized between the boss and the sensor.

 

Are you doing it on your back or from standing with the car above you?

 

It's up on drive on ramps so on my back.

That open sided socket @Fruity pasted didn't work for me. Not enough clearance to even get it in, let alone something else to turn it with.

Shouldn't be cross threaded or seized as it hasn't been screwed into the manifold that long.

The front of the exhaust and the bits around the sensor make it a squeeze. I've ordered that funny 22mm bent socket and will find out after the weekend whether it fits!

 

If it hasn't been in long it should be ok- possibly unless copper grease was applied to the threads. I find it really doesn't help on O2 sensors. It got me wondering why new sensors come with a silver looking grease. I think it is nickel based but the Bostik and Loctite varieties seem to be no longer available probably because they are so hazardous.

 

Yeah I noticed the weird locking grey stuff on the new sensor.

I changed the front one a few months ago, took minutes. I literally can't turn a regular head spanner because it's so tightly packed in there. The idea of a pre cat in there blows my mind but that's the Busso in a FWD setup...

Have read suggestions that stainless manifolds/front decat will often smoke the O2 sensors.

 

Finally fitted... Annoyingly that weird bent 22mm open socket didn't even seem like it was needed. As soon as it was on there was little to no resistance and it just started to turn.

What did take a long time was twisting it off by hand. Didn't help the wire obviously twisted and needed to be unwound constantly.

The new one spun on fine, reset the codes and hopefully the saga is finally over.

My specialist claimed to have cleaned the old sensor but it looked pretty gummed to me. Little white lie? Although it may get caked fairly fast down there....

 

If anyone is looking for anti seize products...Cromwell online shop

 

Bumping this post.

I need to replace the rear bank sensor on my GTA and access from the top seems very tight. I also have the CF3 precats still in place so I'm guessing this makes things even more difficult? Any tips, my local garage did the front but didn't want to touch the rear one for lack of access!

 

Bumping this post.

I need to replace the rear bank sensor on my GTA and access from the top seems very tight. I also have the CF3 precats still in place so I'm guessing this makes things even more difficult? Any tips, my local garage did the front but didn't want to touch the rear one for lack of access!

It's not a very pleasant job. Getting the heatshield off and back on is probably the worst of it. If the lambda sensor is too tight to crack off or it strips the threads you might need to remove the manifold. It's easiest to unbolt with the engine in its normal position, but to actually get the manifold out you need the subframe off, or maybe it's do-able if you get something under the engine and undo all the engine mounts so it can be pulled forward a bit - I've never tried it that way as doing it on a ramp, its easy enough to take the subframe off. There are some good lambda sensor removal tools you can buy to help, I got a set like this one from Euro Car Parts: Laser 3750 7 Piece Lambda Sensor Socket Kit - Machine Mart - Machine Mart