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Diagnosis & Repair

WARNING: This page is about a different car, the 2003 Lexus LS 430. However, it is still accessible from the selected car via links, so may be relevant.
  1. Remove the engine room ECU cover. Turn the ignition switch ON. Measure the voltage between terminals VPTK and EPTK of the ECM connector. See Figure. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest system.
    NOTE: DO NOT apply more than 19.7 in. Hg of vacuum to vapor pressure sensor.
  2. Measure the voltage between terminals PTNK and EPTK of the ECM connectors. Disconnect the vacuum hose from the vapor pressure sensor. Using the MITYVAC (hand-held vacuum pump), apply a vacuum of 1.18 in. Hg (4.0 kPa) to the vapor pressure sensor. Voltage should be 2.9-3.7 volts with vacuum hose disconnected, then 0.5 volts or less with vacuum applied. See Figure. If okay, replace ECM and retest system. If voltage is not as specified, go to next step.
  3. Check for an open or short circuit in wiring harness and connectors between vapor pressure sensor and ECM. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, replace vapor pressure sensor and retest system.
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