Sensor, Fuel Tank Pressure: Description
- The Fuel Tank Pressure Sensor (FTPS) measures the pressure in the evaporative system (the vapor space of the fuel system) and converts it into a voltage. The conversion is a straight line "slope" - therefore, for every unit of vacuum change there is a proportional output voltage change. When purge is turned on (or increased), the Powertrain Control Module (PCM) will see a change in the voltage input. Likewise, when purge is turned off (or decreased), the PCM will see the opposite change in the voltage input. This is how the purge monitor diagnostic for On-Board Diagnostics (OBD) II is accomplished.
- The purge monitor diagnostic is a "pass" when the FTPS measures the minimum acceptable changes in vacuum due to the changes in purge flow. This ensures that the system is functioning as expected. It means that the carbon canister is being "cleaned" by engine purge. If the hose between the engine and the purge valve is compromised, the FTPS will not provide acceptable output. The purge monitor diagnostic is a "fail" if the PCM does not see the calibrated threshold values for any reason.