Disconnect hose between EVAP 2-way valve and fuel tank pressure sensor at EVAP 2-way valve end. Connect vacuum pump to open end of disconnected hose. Turn ignition on. Measure voltage between PCM 32-pin connector terminal No. 29 (Light Green wire) and PCM 31-pin connector terminal No. 18 (Green/Blue wire). Using vacuum pump, carefully apply vacuum one stroke at a time. If voltage smoothly drops from about 2.5 volts to about 1.5 volts, system is okay. Check for intermittent poor connection at fuel tank pressure sensor hoses. If voltage does not smoothly drop from about 2.5 volts to about 1.5 volts, replace fuel tank pressure sensor.
NOTE:
Stop applying vacuum when voltage drops to about 1.5 volts. Damage to fuel tank pressure sensor may occur.