Vapor Pressure Sensor Circuit

Disconnect vapor pressure sensor connector. Sensor is mounted on EVAP charcoal canister underneath rear of vehicle and has a Black 3-pin connector. See Figure-Figure . Turn ignition on. Measure voltage between terminals E2 and VC at vapor pressure sensor connector terminals. See Fig 1. 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 WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM.

Fig 1: Testing Vapor Pressure Sensor
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Turn ignition off. Reconnect vapor pressure sensor connector. Access ECM harness connectors in left front of engine compartment. Disconnect vapor pressure sensor vacuum hose. See Fig 1. Connect vacuum/pressure pump to vapor pressure sensor. Turn ignition on.
Backprobing, measure voltage between following ECM terminals:
- On GS300, terminals No. 18 (Blue/Yellow wire) at ECM E5 connector and No. 18 (Brown wire) at ECM E3 connector. See Figure.
- On IS300, terminals No. 18 (Pink/Green wire) at ECM E4 connector and No. 18 (Brown wire) at ECM E6 connector. See Figure.
- On GS430, terminals No. 25 (Blue/Yellow wire) at ECM E5 connector and No. 26 (Brown wire) at ECM E5 connector. See Figure.
- On LS430, terminals No. 25 (Light Green/Red wire) at ECM connector E2 and No. 26 (Brown/White wire) at ECM E2 connector. See Figure.
On all models, 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.