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DTC P0108 (P_SHI): Pressure Sensor Circuit High Input

  1. Connect scan tool. Start engine. Observe display for intake manifold absolute pressure. If display reads 41.34 in. Hg or less, go to next step. If display reads more than 41.34 in. Hg, go to step 8).
  2. Using voltmeter connected to ground, backprobe PCM connector terminal No. 21 (Red/wire). If voltage is more than 4.5 volts, go to next step. If voltage is 4.5 volts or less, check while wiggling wiring and connector of PCM. If voltage changes, repair poor contact in wiring or PCM connector. If voltage remains 4.5 volts or less, replace PCM.
  3. Using voltmeter connected to ground, backprobe PCM connector terminal No. 26 (Green/Orange wire on Forester and Impreza, or Green wire on Legacy). If voltage reading is .2 volt or less, go to next step. If voltage reading is more than .2 volt, check if scan tool display of atmospheric absolute pressure reading changes while wiggling PCM wiring and connector. If reading changes, repair poor contact or wiring at PCM. If reading does not change, go to next step.
  4. Turn ignition off. Disconnect pressure sensor connector. Turn ignition on. Check voltage between ground and pressure sensor connector terminal No. 3 (Red wire). If voltage is more than 4.5 volts, go to next step. If voltage is 4.5 volts or less, repair open circuit in wiring or poor contact at PCM or pressure sensor connectors.
  5. Turn ignition off. Disconnect PCM connector. Check resistance of harness between PCM connector terminal No. 26 and pressure sensor connector terminal No. 2 (Green/Orange wire on Forester and Impreza, or Green wire on Legacy). If resistance is one ohm or less, go to next step. If resistance is more than one ohm, repair circuit wiring or poor contact in PCM or pressure sensor connectors.
  6. Check resistance of wiring between PCM connector terminal No. 20 and pressure sensor connector terminal No. 1 (Red/Green wire on Forester and Impreza, or Red/Yellow wire on Legacy). If resistance is one ohm or less, go to next step. If resistance is more than one ohm, repair circuit wiring or poor connection in PCM and pressure sensor connectors.
  7. Check pressure sensor connector for poor contact. If connector has poor contact, repair as necessary and retest system. If connection is okay, replace pressure sensor and retest system.
  8. Turn ignition and scan tool off. Disconnect pressure sensor. Turn ignition and Scan tool on. Observe intake manifold absolute pressure signal. If value is more than 41.34 in. Hg, repair short circuit in wiring between PCM and pressure sensor connector. If value is less than 41.34 in. Hg, replace pressure sensor.
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