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Lotus Service Notes Section EMN
Page 15
EMN.12 - OXYGEN (O2) SENSOR
The MEMS system operates a 'closed loop' fuel control system whereby the output signal from an oxygen
sensor in the exhaust system is monitored by the ECM, which constantly adjusts the air/fuel ratio to that
providing the most efficient conversion of gases by the catalyst. A lean air/fuel ratio causes a high exhaust
oxygen content, which reduces the sensor output voltage to the ECM. The air/fuel ratio is then adjusted to be
richer, resulting in reduced exhaust oxygen and a higher sensor output voltage. In this way the mixture
strength constantly sways either side of the ideal setting.
The sensor is equipped with an integral heating element to ensure that it reaches operating temperature
soon after a cold start. The heater element supply is controlled by the ECM via a relay in the relay module.
Using the 'Lotus Check' tool, 'O2 VOLTAGE' shows the voltage across the sensor as read by the ECM.
Once the engine is fully warm, and during most idle and driving conditions, this voltage will switch rapidly
between 0.7 V - 1.0 V. The 'FEEDBACK' display indicates the current feedback fuelling correction. This is
shown as a percentage of the mapped (open loop) value. This percentage is continuously updated by the ECM
whenever the conditions for closed loop fuelling are present. At other times, the feedback value will show
100% indicating that the system is running open loop. High values of feedback (e.g. 120%) indicate that
feedback is attempting to compensage for fuelling being too lean, and low values (e.g. 80%) for fuelling being
too rich. Note: misfire conditions will be shown as high values as feedback will be fooled into compensating for
a system running too lean.
The sensor is mounted on the inner side of the exhaust manifold just upstream of the downpipe flange.
To remove the sensor, unplug and free the electrical connector, and use a 22 mm crows foot spanner to release
the sensor from the manifold. Fit a new sealing washer to the sensor before tightening to 55 Nm and mating
the electrical connector plug.
Oxygen
(O2 ) sensor
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