Functional Description - Fuel Tank Pressure (Ftp) Sensor

Since the vacuum hose between the Purge Solenoid and Intake Manifold cannot be checked during the small leak diagnostic, the FTP Sensor is used to monitor the Evaporative System pressure change during purging to determine if the hose is disconnected or restricted. The PCM uses the FTP Sensor for the purge system performance diagnostics.  The diagnostic works in two phases:

• First the Purge Solenoid is actuated and the PCM monitors the change in the FTP Sensor reading over time. The PCM expects to see the pressure/vacuum reading decrease more than a calibrated threshold over a calibrated period.
• The Purge Solenoid is then deactivated and the PCM monitors the change again over time. The PCM expects to see the pressure reading increase more than a calibrated threshold over a calibrated period.

If either diagnostic fails the threshold, the purge performance fault is set.