[Rolebama]

I've been told my car needs a new exhaust knock sensor. Searched on Bosch website and found brilliant description of what it does. My question is: What are they made of? I have known the guy that owns/manages the workshop for over 30yrs, and I don't think for one moment ha is ripping me off, but he told me the last one of the type my car needs cost over £500! Why - are they a gold case filled with diamonds or something? Anybody any ideas. Thanks.

[Rolebama]

(Hides behind curtain stage left to hide embarrassment). NMNeill, you are quite right, it was a misunderstanding. I have now spoken to him again and got him to spell 'knock', to which he of course replied 'N - O - X'. Makes a lot more sense.

[NMNeil]

There's no such thing as an exhaust knock sensor.
The knock sensor, normally a piezo crystal, is mounted to the engine block.
If you advance the ignition to a certain point the fuel/air mix will detonate, rather than burning in a controlled fashion. For maximum performance and efficiency the engine should run with the timing set so the engine is just below the knock threshold, so the PCM will 'listen' for the knock sensor and keep advancing the ignition until it detects a knock, it will then retard the ignition to keep it just under that threshold. All done in well under a microsecond.
The exhaust has an O2 or Lambda sensor which, as the name implies senses how much oxygen is in the exhaust gas and adjusts the injector timing to give the perfect 14.7 to 1 air fuel ratios, again for optimum performance and efficiency.
They don't go together, one is for fuel mixture the other is for spark timing.
(It was on the test I took a very very long time ago)
https://www.ase.com/uploads/L1Studyguide2021_210112_141625.pdf

As for costing 500 quid🤣
https://www.autozone.com/engine-mana...357/577503_0_0

[NMNeil]

But the 500 quid still doesn't make much sense.
https://www.oreillyauto.com/detail/c...d-taurus?pos=0
And that's for a genuine Bosch sensor

[Rolebama]

NMNeill, could be a translation error, but that is what we call a Lambda sensor. This is what I believe is the part they are on about. (This page is from a generic parts dealer, not necessarily a genuine BMW part.)
https://www.eurocarparts.com/search/...SABEgJNrvD_BwE

[NMNeil]

Originally Posted by Rolebama

NMNeill, could be a translation error, but that is what we call a Lambda sensor. This is what I believe is the part they are on about. (This page is from a generic parts dealer, not necessarily a genuine BMW part.)

They are one in the same.
https://en.wikipedia.org/wiki/Oxygen_sensor
But I still say that 500 quid is excessive.

[Rolebama]

There seems to be a huge price difference for stuff bought in the US and UK. Years ago I had a friend who was a Flight Engineer with British Airways. I asked him to price up a Minolta 3xi camera body only for me. A dealer in New York wanted $300 (around £250 at the time) for a complete kit with lens, case etc. The best price here was £300 for a secondhand body. We are completely ripped off here for just about everything. Current 'excuses' for stupid price hikes include fuel costs, Brexit, Covid and the World Trade Organization charging for imports.