Circuit Description

The control module monitors the fuel tank pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the evaporative emission (EVAP) diagnostic test. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. This DTC sets if the engine control module (ECM) detects one of the following conditions:

• The FTP sensor signal voltage is not within a calibrated range on a cold start-up.
• The FTP sensor signal does not change by a calibrated amount when purge is active.
• The FTP sensor signal oscillates more than a calibrated amount when vehicle speed is less than 30 km/h (50 mph).

The following table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum.