sigma150 cat bypass

[Turbot1]

Daft question but if I use the cat bypass pipe what happens to the lambda sensor? How does that impact the fuel injection? And obviously performance

[mharris]

The cat bypass pipe has a threaded boss for the lambda sensor exactly the same as the catalyst.

In my experience the lambda sensor doesn't do that much. Mine was broken (and therefore being ignored by the ECU) for some time, and it wasn't until I saw the error code in Easimap that I replaced it. The car ran exactly the same with both broken and new lambda sensor. The car even passed its MOT emissions test with the broken sensor.