Vapor Pressure Sensor Circuit

1. Remove left front fender liner. Disconnect vapor pressure sensor connector. Sensor is located on firewall next to brake booster. Turn ignition on. Measure voltage between Blue/Red wire and Brown wire at 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. Connect Check Harness "A" (SST 09990-01000) to ECM. See TEST PREPARATION under SELF-DIAGNOSTIC SYSTEM in TESTS W/CODES article. Disconnect vapor pressure sensor vacuum hose. Turn ignition on.
4. Measure voltage between terminals No. 30 (Red wire) at ECM "A" connector and No. 65 (Brown wire) at ECM "B" 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.