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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
  1. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe and measure voltage between terminals No. 18 (Yellow wire) and No. 28 (Brown wire) at ECM harness connector E10. 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.
  2. Using DVOM, backprobe ECM connector and measure voltage between terminals No. 21 (Pink wire) at ECM harness connector E6 and terminal No. 28 (Brown wire) at ECM harness connector E10. See Figure. Disconnect vacuum hose from vapor pressure sensor. Vapor pressure sensor is mounted on charcoal canister. Connect a vacuum pump to vapor pressure sensor. Voltage should be 2.9-3.7 volts without vacuum applied, and less than .5 volt with 1.18 in. Hg applied. If voltage is as specified, replace ECM. If voltage is not as specified, go to next step.
  3. Check for open or short in wiring between vapor pressure sensor and ECM. See WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace vapor pressure sensor.
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