MEFI Fuel Injection
Sensor Input
Over or under volts for a minimum length of time
A/D Converters And Circuits
The ECM receives voltage signals from the sensors via A/D (Analog to Digital) converters. These A/D converters are the ECM’s voltmeters. The normal voltage signal from a sensor may range from as low as 0.1 volt, to as high as 4.9 volts. This would be the sensor’s operating parameter or “window”. Each sensor has a different operating window. If a sensor is within acceptable parameters, the ECM does not detect a problem. When a sensor signal voltage input falls outside of this window, the ECM sees this as an invalid input voltage and after a programmed length of time will store a DTC. Once a DTC is set, the ECM defaults to a preprogrammed value for the lost sensor to restore limited engine performance. A sensor can report back incorrect information but the signal voltage still be within the operating window. This can cause engine performance problems without setting a DTC. Mechanical problems usually do not set a DTC, however, if severe enough, could possibly drive a sensor outside it’s operating window. Remember; to set a DTC, a sensor’s voltage must go out of range for a minimum length of time. If the sensor voltage goes out of range, but comes back before the timer has timed out, no DTC will be set. The ECM will believe the sensor input and react to it. This will cause some sort of owner complaint about runability with no fault codes. Some rationality checks are also performed.
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