Lambda

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Oxygen sensor

Upstream (Before Cat) oxygen sensors is used to regulate the AFR by sensing the amount of exhaust oxygen. while the downstream (After cat) oxygen sensors are used by the PCM to measure catalytic conversion effeciency. Below are healthy values at idle for a N52 engine.

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# Before Catalytic After Catalytic Lambda
Bank 1 2.00V ~ 2.04V 0.70V ~ 0.80V 1.00
Bank 2 2.00V ~ 2.04V 0.70V ~ 0.80V 1.00
A lambda value less than 1.0 means the engine is running rich, while a value greater than 1.00 implies a lean mixture.
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