二次空气系统诊断
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Secondary air system
The performance of the secondary air system was previously tested via the lambda control value. This means that the voltage present at the probe before the catalyst must indicate a lean mixture during secondary air discharge (l>1) although the engine control unit is running the engine on a rich mixture.
Flow rate diagnosis
Since the introduction of the broadband lambda probe, the signal from the probe before the catalyst is used for diagnosis purposes, because the broadband lambda probe supplies more detailed measurement results than the step type lambda probe for example. The actual air mass flow is calculated and checked on the basis of the lambda differential (lambda value before and during secondary air discharge).
— “Euro On-Board Diagnostic System For petrol engines Self-Study Programme 231″, © VOLKSWAGEN AG, Wolfsburg
