Vapor Pressure Sensor Circuit (RX300)
WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2003 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
- Disconnect vapor pressure sensor electrical connector. Sensor is mounted on top of fuel tank. See Fig 1. Manufacturer recommends lowering fuel tank to gain access to vapor pressure sensor. Turn ignition on. Measure voltage between terminals VC and E2 at vapor pressure sensor connector terminals. See Fig 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 ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, replace ECM.
- Turn ignition off. Reconnect vapor pressure sensor connector. Access ECM harness connectors behind glove box. Disconnect vapor pressure sensor vacuum hose. Connect vacuum/pressure pump to vapor pressure sensor. See Fig 2. Turn ignition on.
- Backprobing ECM harness connector, measure voltage between terminal No. 18 (Brown wire) at ECM E8 connector terminal and No. 17 (Blue/Orange wire) at ECM E5 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.