A4 Mk1
Checking lambda control
Function of lambda control
The lambda probes compare the oxygen content in the air with the residual oxygen content in the exhaust gas and send a voltage signal to the control unit. The voltage signal for "Mixture rich" (low level of residual oxygen) is between about 0.5 and 1.0 V (in relation to reference earth). The voltage signal for "Mixture weak" (high residual oxygen) is between about 0...0.5 V (in relation to reference earth). During the transition from "rich" to "lean" and vice versa (λ = 1.0), there is a voltage jump from 0.5...1.0 V to 0...0.5 V or vice versa. Because of the sharp voltage jump the lambda control cannot maintain a constant ideal mixture composition of λ = 1.0. The system fluctuates continuously between "slightly too lean" and "slightly too rich". If the voltage does not change or only changes slowly the following faults are possible:
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