DTC P0452 (TNKP_Low): EVAP Emission Control System Pressure Sensor Low Input (Forester & 2.5L IMPREZA)
- Turn ignition off. Remove and reinstall fuel filler cap. Connect scan tool. Turn ignition on. Observe fuel tank pressure sensor signal. If displayed value is less than -0.827 in. Hg, go to next step. If value is -0.827 in. Hg or more, system is normal. Check for intermittent open or short in wiring between fuel tank pressure sensor and PCM connector. If okay, check for poor contact at PCM, or fuel tank pressure sensor.
- Using a voltmeter connected to ground, backprobe PCM connector terminal No. 21 (Red wire) with ignition on. If voltage reading is 4.5 volts or more, go to next step. If voltage reading is less than 4.5 volts, wiggle PCM connector. If voltage reading changes to 4.5 volts or more, check for an open in harness between PCM and fuel tank pressure sensor or for poor contact to PCM. If voltage reading does not change, replace PCM.
- Using a voltmeter connected to ground, backprobe PCM connector terminal No. 4 (Green/Orange wire). If voltage reading is less than 0.2 volt, go to next step. If voltage reading is more than 0.2 volt, observe fuel tank pressure sensor signal. Check if value changes to more than -0.827 in. Hg when wiggling PCM connector. If value changes, check for an open in harness or for poor contact at PCM connector. If value does not change when wiggling PCM connector, go to next step.
- Turn ignition off. Remove right rear quarter interior trim panel. Disconnect Black, 3-pin connector from fuel tank pressure sensor. Turn ignition on. Check voltage between ground and fuel tank pressure sensor connector terminal No. 3 (Red wire). If voltage reading is less than 4.5 volts, check for an open in harness between PCM and fuel tank pressure sensor connector. If voltage reading is 4.5 volts or more, go to next step.
- Turn ignition off. Disconnect PCM connector. Using an ohmmeter, check resistance of harness between PCM connector terminal No. 20 and fuel tank pressure sensor connector terminal No. 2 (Red/Green wire). If resistance is one ohm or less, go to next step. If resistance is more than one ohm, check for an open in harness between PCM and fuel tank pressure sensor connector.
- Check resistance of harness between ground and Green/Orange wire at fuel tank pressure sensor connector. If resistance is more than 500 k/ohms, check for poor terminal contact at fuel tank pressure sensor connector. If terminal contact is okay, replace fuel tank pressure sensor. If resistance is 500 k/ohms or less, check for short in harness between PCM and fuel tank pressure sensor.