S2 ECU

The system works by continually monitoring the outputs from all of the sensors that are used to control the engine emissions (throttle position, MAP, O₂ (pre and post Catalyst), crankshaft position, coolant temperature sensor, etc) and compares the outputs with pre-defined, acceptable ranges, for given engine speed and load. If any sensor moves outside these ranges the system will assume there is a fault and will illuminate the light. The system monitors other factors such as vehicle acceleration (through rate of change of engine speed) and if any of these go outside normal limits again the light will illuminate. Changing any components which affect the performance or emissions of the car (air cleaner, catalyst, wheel/tyre size, etc.) may put the sensor readings out of normal range and the lamp will illuminate. Lotus approved tune up parts will be fully tested to ensure they do not make the lamp illuminate or will be sold as off road/track parts only. The latter will cause the lamp to illuminate and you will not be able to legally drive on the road.

There are a number of safeguards built in which will prevent false illumination of the light in the event of a momentary false reading etc. The number of events necessary to illuminate the lamp depends on the sensor/system being monitored and the amount of the deviation from normal. The system only functions when the engine is running, so a flat battery will not cause the light to illuminate. Once illuminated the light will however stay on, as long as the fault is present. If/when the physical fault is no longer present and the appropriate built-in OBD check has been passed on three consecutive trips, then the MIL will go off. The fault's associated code will still be stored, until the appropriate OBD check has been passed on forty consecutive trips.

Because the system is fully integrated with the engine management system and uses all of the sensors that are needed to run the engine, it is not possible to bypass the MIL. The only method would be to totally replace the engine management system with another non-OBD system. This equates to breaking the law, if then used on the public road, as the car would no longer comply with it's type approval.

The engine management system has been specified to include memory which Lotus intend to use for a future upgrade that will provide a data-logging facility for use on the track. At present this memory is used to gather data needed to onward develop the OBD system. There is also a 'snap-shot' logging facility which records the sensor outputs at the moment a fault is triggered to aid diagnosis by a dealer. There is no 'black-box' system for accident investigation but, the data captured can be used by Lotus to check on how the car has been used during it's life. This information could be used to decide whether a warranty claim is justified or not. The data recorded includes the percentage of time spent at each of five throttle opening bands, five engine speed bands, five wheel speed bands and five manifold pressure bands. Further data on time spent at various coolant and oil temperature bands is also collected. Additionally it records data on the maximum engine speeds attained at certain coolant temperatures, the five highest vehicle speeds recorded total engine running time and the fastest and latest 0-100 kmh and 0-160 kmh times. The system also recognises and records the number of full load standing starts performed. The data is not linked to any real-time system and cannot therefore be used by other authorities as it is not possible to determine when or where any of the data was recorded. No customer details are recorded in accordance with the data protection act. It is not possible to clear the memory. The data can be accessed by the dealer using an interrogation tool, and copies are returned to Lotus. It was not intended that this data be shared with the customers, but there's no reason why your dealer can't let you have a look.

All this has massive implications for the tuning companies and is one reason why Lotus are unable to announce precisely what engine upgrades will be offered in the near future. In the UK, Single Vehicle Approval (SVA) cars appear to be exempt at present. After market accessories have to be tested to see if they trigger the MIL and replacement of the K4 ECU is not legally allowed under the new legislation. This effectively means that third parties are very limited in what they can offer unless they work with Lotus to reprogram the ECU.

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