| The lambda probe compares the oxygen content of the air with the residual oxygen in the exhaust gas and supplies a voltage signal to the engine control unit. |
| The voltage signal “mixture rich ” (little residual oxygen) is at approx. 0.7..1.0 V (related to reference mass). |
| The voltage signal “mixture lean” (high level of residual oxygen) is at approx. 0.0...0.3 V (related to reference mass). |
| During the transition from “mixture rich” to “mixture lean” and vice versa there is a voltage jump from 0.7 to 1.0 V to 0.0 to 0.3 V or vice versa. |
| In view of the steep voltage jump the lambda control is not able to maintain constant the ideal mixture composition which corresponds to the l = 1.0. |
| A so-called reference voltage of approx. 0.4 to 0.5 V has been programmed into the engine control unit to analyse the lambda probe signal. The control constantly fluctuates back and forward between the “slightly too lean” and “slightly too rich” states. |
| At idling speed and with a warm engine, the control must operate at least 30 times per minute. |
| If the voltage change does not occur, or if it is too slow, the following faults may have occurred: |
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| The slots or holes in the lambda proble head are clogged up. |
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| The ventilation hole on the probe -near the connecting cable - is closed. |
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| The probe was overheated. |
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| The probe was damaged by leaded fuel. |
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| Transition resistance in the signal line. |
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| The probe too cold, the lambe probe heater does not operate. |
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| The lambda control is switch off (engine control unit has detected a fault at the injection system, interrogate fault memory → Chapteras well as read measured value block, display group 021 → Chapter). |
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| Probe damaged by contact spray or similar (because of the thermal fluctuations and the capillary effect the contact spray is sucked into the probe via the fine hollow spaces in the electrical lines). |
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| The probe damaged by silicone vapours. (When using silicone sealants traces of silicone particles are sucked into the engine. These silicone particles are not combusted and damage the lambda probe). |
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| The probe was damaged by oil particles escaping from the crankcase housing ventilation or by engine leaks. |
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