Vapor Pressure Sensor Circuit

1. Disconnect vapor pressure sensor connector. Sensor is located on firewall next to brake booster. 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. Repair as necessary. If wiring is okay, replace ECM.
3. Turn ignition off. Reconnect vapor pressure sensor connector. Access ECM behind glove box. Disconnect vapor pressure sensor vacuum hose. Turn ignition on.
4. Backprobing ECM harness connector, measure voltage between terminals No. 13 (Blue/Red wire) at ECM E8 connector and No. 22 (Brown wire) at ECM E9 connector. See Figure. 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.