Vapor Pressure Sensor Circuit

1. Disconnect vapor pressure sensor connector. Turn ignition on. Measure voltage between vapor pressure sensor connector terminals.
2. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, check wiring harness between sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. See Figure-10. Repair as necessary. If wiring is okay, replace ECM.
3. Turn ignition off. Reconnect vapor pressure sensor connector. Excess ECM. Disconnect vapor pressure sensor vacuum hose. Turn ignition on.
4. Backprobing ECM harness connector, measure voltage between terminals and at ECM connector. Voltage reading should be as follows:
   • 3.0-3.6 volts with no vacuum applied.
   • 1.3-2.1 volts with .59 in. Hg (2.0 kPa) of vacuum applied.
   • 4.2-4.8 volts with .22 psi (1.5 kPa) of pressure applied.

If voltage is not as specified, replace vapor pressure sensor.