A3 Mk1
Testing lambda control
Operation of lambda control
Notes: The lambda probe compares the oxygen content in the air with the residual oxygen content in the exhaust gas and sends a voltage signal to the control unit. The voltage signal for "Mixture too rich" (low residual oxygen) is between about 0.7 and 1.1 V (based on reference earth). The voltage signal for "Mixture too lean" (high residual oxygen) is between about 0.0 and +0.3 V. The transition from "rich" to "lean" is accompanied by a voltage jump from between 0.7 and 1.0 V to between 0.0 and +0.3 V, and vice versa (λ = 1.0). 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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