Error code advice - pre-cat lambda sensor

[miniyazz]

I'm considering a new (old) car, namely a Jag S-type 4.2L n/a
So torn between spending (much) more and getting a better one or spending less and getting one needing a bit of work. The cheapskate in me says the latter; realistically the difference in cost is a couple of grand.

Now the car I'm looking at has a few cosmetic issues none of which are particularly major (bits of missing trim, that sort of thing) but also has a check engine light and a check of the fault codes have revealed an issue with the bank 1 sensor 1 O2 sensor. The car also has an irregular idle. It seems to drive fine without any obvious gearbox issues.

So I suppose my question is, how much is it likely to set me back to sort out the pre-cat O2 sensor? My local garage muttered something about £2-300 and advised me to steer clear

 

[miniyazz]

Yeah well that's the question really, whether the lambda is the cause or just a symptom. Is it feasible for a pre-cat lambda to be causing a dodgy idle?

It's a 2006 so should be more reliable than the earlier models. I'm not under any illusions that it'll be as cheap to run as a golf though.


As a side note, the garage confused me by suggesting that there would be 6 lambda sensors on a car like this - one on the manifold, one pre-cat and one post-cat (x2 as two banks). Is that right? I thought there would just be four..

 

[miniyazz]

Alright thanks. The other question is whether the lambda sensor causing a dodgy idle could cause problems with the cat - if there's a misfire this is obviously a concern - but there wasn't a code for an impending error relating to misfiring, which I thought came up pretty quickly with a misfire.

 

[miniyazz]

TBH it wasn't even that noticeable from inside the car, it was simply that I could see the idle speed fluctuating on the rev counter between ~6-900rpm. Apparently it's been on for about a year because they got it checked out and were told it was nothing more serious than a dodgy sensor and because the car still drove fine

This business about having 6 lambda sensors is confusing me though, why would there be three sensors per bank? Or was my mechanic talking rubbish?

 

[miniyazz]

Nahh there's 2 Lambdas before the cats and 2 after the cats on each bank (4 total), the ones after the cats rarely fail and wouldn't cause a idling problem, just high emissions which btw your car will also have.

But post-cat O2 sensors failing wouldn't cause high emissions. All they do is monitor the cat efficiency (and trip if they think the cat is faulty), the car doesn't act on any data from them except to trip a fault code.

 

[miniyazz]

I'm going to have another look at it. Realistically it's unlikely to cost me the difference between it and a car potentially without these issues and once you factor in the spec which is quite rare with e.g. adaptive cruise control I think I probably will go for it yes but will probably try to knock a little more off.