Analog To Digital Signal Description

Electronic Control Modules read analog signal voltages and convert them to digital counts. Each count is an equal percentage of the voltage. This can be seen when viewing the voltages of some sensors or switches on the scan tool. The values will change in blocks (Ex. 0.08v, 0.12v, 0.16v or 8 Pa, 16 Pa, 24 Pa etc.). The signal voltage could be anywhere from 5.0 volts on most sensors to a battery voltage reference on switches.

• The resolution of the signal is determined by the required precision of the input by the ECU. Typically, sensor signals have a high resolution (Ex. a sensor signal may be divided into 4096 counts, or 5.0 volts divided by 4096). This allows the module to read small changes over a wide range in a variable resistance sensor signal used for a temperature, pressure, or position sensors.
• Switches will typically have a low resolution since they are usually only reporting a few switch states (Ex. a switch may typically be divided into only 15-20 counts, or Battery voltage divided by 15). The highest and lowest one or two counts will be used for detecting opens or shorts if the switch signal is being rationalized. The remaining counts are divided up between the states being detected.