There are many modes where the ECU will do something to keep the engine running, when something is not proper.. It's often referred as Safety Mode, Or Limp Mode.. I hate both terms.. If the Water Temp Sensor is missing a Sig, the ECU will 'Assume' a Temperature Profile based upon how long the Engine has been running, and 'Fake' a Water Temp for the ECU Calculations.. Generally this is not a 'Serious' ECU Error... And you might not even know its doing it.. If the O2 Sensor is not giving a reliable Reading, the ECU will just use the previous Fuel Trim to do it's Calculations.. This COULD be a major problem ( Or Not ) depending on the Driving Conditions and the 'Quality' of the Sensor Data before it went Tits Up.. If the ECU can not find any Valid ROM Data, it will fall back to some 'Air Flow' or TPS Position VS fuel Delevery, to allow you to get your car off the road and on to a Flat Bed.. You will know when this happens.. as the car runs like Krap.. There are other conditions that the ECU will have programmed into it to allow you to Move/Operate your car to get it to a shop.. To Operate your car for any length of time, or considering racing your car with something other than a COMPLETE Engine Management System is utter stupidity.. Cj
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