Why does the engine need both pre and post cat O2 sensors? AFAIK the pre ones talk to the ecu and help keep the air/fuel ratio in check, what are the after cat ones for then?
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Why does the engine need both pre and post cat O2 sensors? AFAIK the pre ones talk to the ecu and help keep the air/fuel ratio in check, what are the after cat ones for then?
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The front two monitor the AFR for the DME and the rears monitor the CATS.
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What do you think of the notion that they should be changed at 100k?
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Mine were gone at 80.
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If I remember correctly I got bosch sensors for an m3 at an okish price from euro car parts. I would imagine they would be the same sensor. Plenty of crud on the old ones so I could see why new ones would be a benefit.
I did the same, bought Bosch units on amazon for mine and they were a fraction of the price of OE
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Notice much of a difference after?
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Just a smoother and cleaner power delivery, emissions were much better too.
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Had you lights on the dash before?
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No, but it failed the NCT and the readings seemed out on INPA
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